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A C++ library for reading, writing, creating and modifying Microsoft Excel® (.xlsx) files.

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# OpenXLSX

OpenXLSX is a C++ library for reading, writing, creating and modifying
Microsoft Excel® files, with the .xlsx format.

# The OpenXLSX project has moved to Codeberg

**NOTE: With today's release v0.5.1, this repository is discontinued on github. It has been migrated to [Codeberg](https://codeberg.org/lars_uffmann/OpenXLSX), and will eventually be moved to [@troldal's Codeberg](https://codeberg.org/troldal/OpenXLSX).**

Please do not open any more issues or pull requests on github, and instead submit your feature requests directly on [Codeberg](https://codeberg.org/lars_uffmann/OpenXLSX/issues).

After [creating an account on codeberg.org](https://codeberg.org/user/sign_up), you will be able to "own" and edit issues and comments previously created by you by linking your github account to codeberg via ["Sign in with Github"](https://codeberg.org/user/login), direct link [here](https://codeberg.org/user/oauth2/GitHub).

## Library Version 0.5.1

This version, with updates from 2026-06-13, is the [latest release](https://github.com/troldal/OpenXLSX/releases).

## Table of Contents

- [To-Do list](#to-do-list)
- [Most recent changes](#most-recent-changes)
- [Motivation](#motivation)
- [Ambition](#ambition)
- [Compatibility](#compatibility)
- [Build Instructions](#build-instructions)
  - [Install `cmake` & `git` on debian-based Linux distributions](#install-cmake-git-on-debian-based-linux-distributions)
  - [Install `cmake` & `git` on Windows 10/11 (for now only tested with `MSYS Makefiles`)](#install-cmake-git-on-windows-10-11-for-now-only-tested-with-msys-makefiles)
  - [Build the OpenXLSX library](#build-the-openxlsx-library)
  - [Integrating into a CMake project structure](#integrating-into-a-cmake-project-structure)
  - [Building as a separate library](#building-as-a-separate-library)
- [How to compile and link a program against an installed OpenXLSX library](#how-to-compile-and-link-a-program-against-an-installed-openxlsx-library)
  - [Build your program using g++](#build-your-program-using-g)
  - [Build your program using cmake](#build-your-program-using-cmake)
- [Current Status](#current-status)
- [Performance](#performance)
- [Caveats](#caveats)
  - [File Size](#file-size)
  - [Memory Usage](#memory-usage)
  - [Unicode](#unicode)
- [Reference Guide (to be written)](#reference-guide)
- [Example Programs](#example-programs)
- [Changes](#changes)

## To-Do list

**Note:** generally, for features awaiting implementation, refer to the open issues in the repository

* tables/filters
* true hyperlink support
* postponed (may not be done at all): when OPENXLSX_MONOLITHIC_LIBRARY=ON, use target_link_interface instead of target_link_library for remaining dependencies (libzip/miniz, pugixml) to allow installing only monolithic library (currently the monolithic file is built, but not installed)
* XLStyles: support predefined number formats with constants that have meaningful names
* XLWorksheet: support for XML comments
* XLWorksheet: support for Rich Text elements in cell strings
* TBD: implement `BUILD_SHARED_LIBS` functionality in `Makefile.GNU`
* TBD: in `Makefile.GNU`, check for available dependencies and error out if any are missing

## Most recent changes

For the latest functionality updates, please refer to the development branch. Feel free to [have a look](https://github.com/troldal/OpenXLSX/tree/development-aral). This way you don't have to wait until the main repository is updated.

### (aral-matrix) 13 June 2026 - major changes to cmake configuration, some minor patches
* upped OpenXLSX library version to `0.5.1` - git tag will be updated in one of the next commits
* cmake should now correctly find locally installed library versions, including determining the library type if required (`OPENXLSX_MONOLITHIC_LIBRARY` requires static, `BUILD_SHARED_LIBS` requires shared dependencies) and triggering (if enabled) automatic download from upstream if the required dependency is not available
* cmake: cleaned up debugging output, replaced message log level NOTICE with STATUS in most places since I learned that NOTICE is directed to stderr, not stdout
* XLXmlParserForwardDeclarations.hpp: added forgotten API declaration for XML namespace support
* XLDocument::create bugfix for unicode paths: use nowide functions for creating temp file, addresses #399
* XLDocument::create bugfix preventing deletion of temporary workbook template file: load document into memory, close file handle, then initialize archive from memory
* Zippy.hpp & LibZip.hpp loadArchiveData bugfix: changed fopen file mode from r to rb (binary)
* XLStyles bugfix: root XML nodes are now created (if necessary) with a sorted insertion using m_nodeOrder
* XLProperties, XLAppProperties, XLVmlDrawing, XLWorkbook bugfixes: ensure required XML namespaces of document root node
* XLWorksheet: constructor now always deletes the worksheet's <dimension> tag - added `void XLWorksheet::setDimension` functions to set it, with auto-calculation of last cell, if desired. This addresses [issue 361](https://github.com/troldal/OpenXLSX/issues/361). Supported function overloads:
```
void XLWorksheet::setDimension(XLCellReference topLeft, XLCellReference bottomRight, bool autoCalculateLastCell);
void XLWorksheet::setDimension(std::string topLeft, std::string bottomRight);
void XLWorksheet::setDimension(std::string dimension);
```

### (aral-matrix) 19 April 2026 - vcpkg compatibility maximized, some improvements/bugfixes in cmake configuration
* vcpkg support should now be as good as it gets: Big thank you to [@bansan85](https://github.com/bansan85) for maintaining the vcpkg package patches, and supporting the bugfixes / improvements of the cmake configuration so that it behaves well with vcpkg :)
* monolithic library is now available via cmake option `-DOPENXLSX_MONOLITHIC_LIBRARY=ON` - this requires static dependencies and only works with miniz, fails with libzip (or rather: the libzip (sub-)dependencies will not be linked into the resulting bundled library)
* for testing if a destination file exists (`OpenXLSXFileSystemTools.hpp` `pathExists`), `nowide::stat` is now used when nowide is in use. This should make calls to `XLDocument::create` and `XLDocument::saveAs` behave well with filenames containing unicode characters
* added function `OpenXLSXFileSystemTools fileSize` to wrap call to `stat` with nowide compatibility - this is used in `LibZip.hpp loadArchiveData`

## Change history

Change history is found in the [detailed change log](#detailed-change-log).

## May 2024 Update

After a long period of inactivity, I have decided to resume development of OpenXLSX. The code has been cleaned up and a significant number of bugs have been fixed. The library has been tested on Windows, macOS and Linux, and should work on all platforms.

I would like to extend my sincere thanks to all the people who have contributed to the project, either by reporting bugs, suggesting features or by submitting pull requests. I would also like to thank all the people who have starred the project, and who have shown interest in the project.

In particular, I would like to thank Lars Uffmann (https://codeberg.org/lars_uffmann/) for his contributions to the project. Lars has spent significant time and effort in cleaning up the code, fixing bugs and implementing new features. Without his help, the project would not have been in the state it is today.

### 20/05/2024
* Google Benchmark is no longer included in the repository. To run the benchmarks, Google Benchmark have to be installed on the system. If you use vcpkg, it will be downloaded automatically.
* Minor performance improvements to XLCellReference.

### 06/08/2024
* Housekeeping updates to the code.
* Added Makefile.GNU for building on Linux. The project will continue to be based on CMake, and the makefile may not always be kept up-to-date.

## Motivation

Many programming languages have the ability to modify Excel files,
either natively or in the form of open source libraries. This includes
Python, Java and C#. For C++, however, things are more scattered. While
there are some libraries, they are generally less mature and have a
smaller feature set than for other languages.

Because there are no open source library that fully fitted my needs, I
decided to develop the OpenXLSX library.

## Ambition

The ambition is that OpenXLSX should be able to read, write, create and
modify Excel files (data as well as formatting), and do so with as few
dependencies as possible. Currently, OpenXLSX depends on the following
3rd party libraries:

- PugiXML
- Zippy (C++ wrapper around miniz) - an alternative wrapper for libzip can be configured with cmake option `-DOPENXLSX_ENABLE_LIBZIP=ON`
- (Windows only) Boost.Nowide (for opening files with non-ASCII names on Windows)

As of version 0.5.0, these libraries are no longer included in the repository, and there are three ways to build OpenXLSX against them:
1) pre-install the libraries on your operating system - the OpenXLSX cmake configuration should find them via `find_package`
2) auto-fetch the missing dependencies from upstream repositories, build & install them together with OpenXLSX. For this, cmake must be able to find `git`
3) (Windows only) install OpenXLSX via the [vcpkg package manager](https://vcpkg.io/en/package/openxlsx), which handles dependencies for you:

Also, focus has been put on **speed**, not memory usage (although there are options for reducing the memory usage, 
at the cost of speed; more on that later).

## Compatibility

OpenXLSX has been tested on the following platforms/compilers. Note that
a '-' doesn't mean that OpenXLSX doesn't work; it just means that it
hasn't been tested:

|         | GCC   | Clang | MSVC |
|:--------|:------|:------|:-----|
| Windows | MinGW | MinGW | +    |
| Cygwin  | -     | -     | N/A  |
| MacOS   | +     | +     | N/A  |
| Linux   | +     | +     | N/A  |

The following compiler versions should be able to compile OpenXLSX
without errors:

- GCC: Version 7
- Clang: Version 8
- MSVC: Visual Studio 2019

Clang 7 should be able to compile OpenXLSX, but apparently there is a
bug in the implementation of std::variant, which causes compiler errors.

Visual Studio 2017 should also work, but hasn't been tested.

## Build Instructions

OpenXLSX uses CMake as the build system (or build system generator, to be exact) and git to pull in dependencies. Therefore, you must install CMake first, in order to build OpenXLSX. You can find (bad) installation instructions on www.cmake.org. If you wish the cmake to automatically fetch missing dependencies, you also need to install git.

Here is a summary to get a working configuration of cmake + git.

### Install `cmake` & `git` on debian-based Linux distributions

```bash
sudo apt update
sudo apt install build-essential cmake git
```

### Install `cmake` & `git` on Windows 10/11 (for now only tested with `MSYS Makefiles`)

**Install MSYS2:**

* In a Powershell (run as Administrator): run `winget install --id MSYS2.MSYS2 -e`

→ After performing this step, the "MSYS2 MSYS shell" and the "MSYS2 MinGW 64-bit shell" should be accessible from the Start Menu

* In MSYS2 MSYS shell: run `pacman -Syu`

The previous instruction might require a close & reopen of the MSYS2 MSYS shell

* In MSYS2 MSYS shell: run `pacman -Su`

**Install development toolchain:**

In MSYS2 MinGW 64‑bit shell: run `pacman -S --needed base-devel mingw-w64-x86_64-toolchain`

**Install `cmake` & `git` in MSYS2 environment:**

* In MSYS2 MinGW 64‑bit shell: run `pacman -S --needed mingw-w64-x86_64-cmake mingw-w64-x86_64-git`
* (optional if you want to use ninja build tool instead of make) In MSYS2 MinGW 64‑bit shell: run `pacman -S --needed mingw-w64-x86_64-ninja`

**Verify installation:**

In MSYS2 MinGW 64‑bit shell: verify versions of `git`, `cmake`, `gcc`, `g++`

```bash
git --version; cmake --version; gcc --version; g++ --version
```

### Build the OpenXLSX library

In MSYS2 MinGW 64‑bit shell
```bash
git clone https://github.com/troldal/OpenXLSX <destination-folder>

cd <destination-folder>
mkdir build; cd build
```

**Then** build with MSYS Gnu make:
```bash
cmake .. -G "MSYS Makefiles" -DCMAKE_BUILD_TYPE=Release
cmake --build . --parallel
```
*Note*: As of 2026-03-21, this configuration complains about miniz (if used) being incompatible with cmake versions >3.5; the following command sequence can be used to get rid of the warning:
```bash
cmake .. -G "MSYS Makefiles" -DCMAKE_BUILD_TYPE=Release -DCMAKE_POLICY_VERSION_MINIMUM=3.5
cmake --build . --parallel
```

**or** build with MinGW Gnu make (untested - should provide a working configuration that can be compiled from cmd/Powershell)

```bash
cmake .. -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE=Release
cmake --build . --parallel
```

**or** build with ninja (untested)
```bash
cmake .. -G "Ninja" -DCMAKE_BUILD_TYPE=Release
ninja
```

The OpenXLSX library is located in the OpenXLSX subdirectory to this repo. However, the root folder `CMakeLists.txt` establishes the library configuration and dependencies.
If you use CMake for your own project, you can add the OpenXLSX root folder as a subdirectory to your own project.
Alternatively, you can use CMake to generate make files or project files for a toolchain of your choice. Both methods are described in the following.

### Integrating into a CMake project structure

By far the easiest way to use OpenXLSX in your own project, is to use CMake yourself, and then add the OpenXLSX root folder
as a subdirectory to the source tree of your own project. Several IDE's support CMake projects, most notably Visual Studio 2019,
JetBrains CLion, and Qt Creator. If using Visual Studio, you have to specifically select 'CMake project' when creating a new project.

The main benefit of including the OpenXLSX library as a source subfolder, is that there is no need to locate the 
library and header files specifically; CMake will take care of that for you. Also, the library will be built using 
the same configuration (Debug, Release etc.) as your project. In particular, this a benefit on Windows, where is it 
not possible to use Release libraries in a Debug project (and vice versa) when STL objects are being passed through 
the library interface, as they are in OpenXLSX. When including the OpenXLSX source, this will not be a problem.

By using the `add_subdirectory()` command in the CMakeLists.txt file for your project, you can get access to the 
headers and library files of OpenXLSX. OpenXLSX can generate either a shared library or a static library. By default 
it will produce a static library, but you can change that by setting `BUILD_SHARED_LIBS` to `ON`. The library is
located in a namespace called OpenXLSX; hence the full name of the library is `OpenXLSX::OpenXLSX`.

Including OpenXLSX into your project would look like this inside your project's `CMakeLists.txt`:

```cmake
# ============================================================================
# Configure OpenXLSX
# ============================================================================
set(OPENXLSX_CREATE_DOCS           OFF)
set(OPENXLSX_BUILD_SAMPLES         OFF)
set(         BUILD_SHARED_LIBS     OFF)

add_subdirectory( OpenXLSX )
```

Then you can use `target_link_libraries` and `target_include_directories` like so:
```cmake
# Configure linkage for myapp
target_link_libraries(myapp PRIVATE OpenXLSX::OpenXLSX)
target_include_directories(myapp PRIVATE ${OpenXLSX_INCLUDES})
```

For linking against a shared library, you should include the "rpath" into your final applications:
```cmake
# Ensure configuration of install RPATH for myapp
set_target_properties(myapp PROPERTIES
  INSTALL_RPATH_USE_LINK_PATH TRUE
)
```

#### Example CMakeLists.txt and Hello World

The following snippet is a minimum CMakeLists.txt file for your own project, that includes OpenXLSX as a subdirectory. Note that the output location of the binaries are set to a common directory. On Linux and MacOS, this is not really required, but on Windows, this will make your life easier, as you would otherwise have to copy the OpenXLSX shared library file to the location of your executable in order to run.

```cmake
cmake_minimum_required(VERSION 3.14)
project(myapp
    VERSION 1.0.0
    LANGUAGES CXX
)

# ============================================================================
# Example app configuration
# ============================================================================
add_executable(myapp myapp.cpp)

# ============================================================================
# Configure OpenXLSX
# ============================================================================
option(BUILD_SHARED_LIBS              OFF "can be used to build shared library version of OpenXLSX")
set(   OPENXLSX_CREATE_DOCS           OFF)
set(   OPENXLSX_BUILD_SAMPLES         OFF)

add_subdirectory( OpenXLSX )

# Configure linkage for myapp
target_link_libraries(myapp PRIVATE OpenXLSX::OpenXLSX)
target_include_directories(myapp PRIVATE ${OpenXLSX_INCLUDES})

# Ensure configuration of install RPATH for myapp
set_target_properties(myapp PROPERTIES
  INSTALL_RPATH_USE_LINK_PATH TRUE
)

# Installation steps for myapp
install(TARGETS myapp
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
    COMPONENT Runtime
)
```

Using the above, you should be able to compile and run the following code, which will generate a new Excel file 
named 'Spreadsheet.xlsx':

```cpp
#include <OpenXLSX.hpp>

using namespace OpenXLSX;

int main() {

XLDocument doc;
    doc.create("Spreadsheet.xlsx", XLForceOverwrite);
    auto wks = doc.workbook().worksheet("Sheet1");

wks.cell("A1").value() = "Hello, OpenXLSX!";

doc.save();

return 0;
}
```

### Building as a separate library

If you wish to produce the OpenXLSX binaries and include them in your project yourself, it can be done using CMake and a compiler toolchain of your choice.

From the command line, navigate the OpenXLSX subdirectory of the project root, and execute the following 
commands:

```
mkdir build
cd build
cmake ..
```

The last command will configure the project. This will configure the project using the default toolchain. If you 
want to specify the toolchain, type `cmake -G "<toolchain>" ..` with `<toolchain>` being the toolchain you wish to 
use, for example "Unix Makefiles", "Ninja", "Xcode", or "Visual Studio 16 2019". See the CMake documentation for 
details.

Finally, you can build the library using the command:

```
cmake --build . --target OpenXLSX --config Release
```

You can change the `--target` and `--config` arguments to whatever you wish to use.

When built, you can install it using the following command (as superuser / `sudo`):

```
cmake --install .
```

This command will install the library and header files to the default location on your platform (usually /usr/local/ 
on Linux and MacOS, and C:\Program Files on Windows). You can set a different location using the --prefix argument.

Note that depending on the platform, it may not be possible to install both debug and release libraries. On Linux 
and MacOS, this is not a big issue, as release libraries can be used for both debug and release executables. Not so 
for Windows, where the configuration of the library must be the same as for the executable linking to it. For that 
reason, on Windows, it is much easier to just include the OpenXLSX source folder as a subdirectory to your CMake 
project; it will save you a lot of headaches.

## How to compile and link a program against an installed OpenXLSX library

### Build your program using `g++`
With the most recent updates, the OpenXLSX `CMake` configuration will also configure (and install) a pkg-config file for `libOpenXLSX` (and `libminiz`), to simplify linking a program against OpenXLSX for systems on which `pkg-config` is available. Invoking `pkg-config --cflags` will yield the proper include flags, and `pkg-config --static --libs` will yield the linker instructions for the OpenXLSX library and its dependencies (pugixml and zip library).
The sequence of arguments to the compiler is important:
1) cflags (include paths)
2) the cpp file(s) that use OpenXLSX
3) the linker flags (libs)
For this reason, the example compilation + linking command below invokes pkg-config twice.
```
g++ `pkg-config --cflags OpenXLSX` ../Examples/Demo1.cpp `pkg-config --static --libs OpenXLSX`
```
When linking against a shared library, the library runtime search path (`rpath`) should be included in the command. The OpenXLSX package config file provides the `rpath` setting via `pkg-config --libs`, so that the following, simplified line should work:
```
g++ `pkg-config --cflags OpenXLSX` ../Examples/Demo1.cpp `pkg-config --libs OpenXLSX`
```

If this new feature does not work as intended, please try providing the rpath manually:
```
g++ -Wl,-rpath,/usr/local/lib `pkg-config --cflags OpenXLSX` ../Examples/Demo1.cpp `pkg-config --libs OpenXLSX`
```

#### Caution when both the shared and the static library are installed
**CAUTION**: When attempting static linking while the shared library for OpenXLSX is also installed, the `-lOpenXLSX` flag returned from `pkg-config --static --libs OpenXLSX` will fail to link against the static library.
A manual fix like so should work (this is only an example, for libzip configuration, without nowide; see below):
```
g++ `pkg-config --cflags OpenXLSX` ../Examples/Demo1.cpp -L/usr/local/lib -l:libOpenXLSX.a -L/usr/local/lib/OpenXLSX -l:libpugixml.a -l:libzip.a -lpugixml -lbz2 -llzma -lzstd -lssl -lcrypto -lz
```

**Note** that you will have to adjust the linker flags according to your configuration:
`-l:libpugixml.a`
`-l:libminiz.a`
`-l:libzip.a` (which requires `-lbz2 -llzma -lzstd -lssl -lcrypto -lz`)
`-l:libnowide.a`

However, the recommended solution for static linking is to not install the shared library (for now - might support different naming in the future).

### Build your program using `cmake`

Below is a simple `CMakeLists.txt` template with all necessary steps to compile & link against an installed version of OpenXLSX.

Steps to test this (assuming OpenXLSX has been installed):
* create a folder `myapp`
* save the below `CMakeLists.txt` template into `myapp/`
* create a folder `myapp/src`
* from the OpenXLSX/Examples folder, copy `Demo1.cpp` into `myapp/src/`
* create a folder `myapp/build`
* change into the folder `myapp/build`
* `cmake ..`
* `make all`
* `./myapp`

#### `CMakeLists.txt` template:
```cmake
cmake_minimum_required(VERSION 3.14)
project(myapp
    VERSION 1.0.0
    LANGUAGES CXX
)

# Find dependency OpenXLSX
find_package(OpenXLSX CONFIG REQUIRED)
if(OpenXLSX_FOUND)
    message( STATUS "FOUND OpenXLSX" )
    get_target_property(OpenXLSX_INCLUDES OpenXLSX::OpenXLSX INTERFACE_INCLUDE_DIRECTORIES)  # get OpenXLSX include directories
    message( STATUS "OpenXLSX_INCLUDES is ${OpenXLSX_INCLUDES}" )
else()
    message( FATAL_ERROR "MISSING DEPENDENCY OpenXLSX" )
endif()

# Configure linkage for myapp
target_link_libraries(myapp PRIVATE OpenXLSX::OpenXLSX)
target_include_directories(myapp PRIVATE ${OpenXLSX_INCLUDES})

# Ensure configuration of install RPATH for myapp
set_target_properties(myapp PROPERTIES
  INSTALL_RPATH_USE_LINK_PATH TRUE
)

# Installation steps for myapp
install(TARGETS myapp
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
    COMPONENT Runtime
)
```

## Current Status

OpenXLSX is still work in progress. The following is a list of features
which have been implemented and should be working properly:

- Create/open/save files
- Read/write/modify cell contents
- Copy cells and cell ranges
- Copy worksheets
- Cell ranges and iterators
- Row ranges and iterators
- Cell content and borders formatting (XLStyles)
- Conditional formatting
- Merged cells
- Worksheet protection (read-only cells, lock with password)
- Cell comments (plain text)

Features related to plots and figures have not been implemented as of yet, and at least plot functionality is not planned to be implemented at all.

It should be noted that creating const XLDocument objects is currently not working!

## Performance

**Note:** As of 2026-04-19 this section is severely outdated. It is not sure how well the numbers from ~2024 hold up with recent changes.

The table below is the output from a benchmark (using the Google
Benchmark library), which shows that read/write access can be done at a
rate of around 4,000,000 cells per second. Floating point numbers are
somewhat lower, due to conversion to/from strings in the .xml file.

```
Run on (16 X 2300 MHz CPU s)
CPU Caches:
  L1 Data 32 KiB (x8)
  L1 Instruction 32 KiB (x8)
  L2 Unified 256 KiB (x8)
  L3 Unified 16384 KiB (x1)
Load Average: 2.46, 2.25, 2.19
---------------------------------------------------------------------------
Benchmark                 Time             CPU   Iterations UserCounters...
---------------------------------------------------------------------------
BM_WriteStrings        2484 ms         2482 ms            1 items=8.38861M items_per_second=3.37956M/s
BM_WriteIntegers       1949 ms         1949 ms            1 items=8.38861M items_per_second=4.30485M/s
BM_WriteFloats         4720 ms         4719 ms            1 items=8.38861M items_per_second=1.77767M/s
BM_WriteBools          2167 ms         2166 ms            1 items=8.38861M items_per_second=3.87247M/s
BM_ReadStrings         1883 ms         1882 ms            1 items=8.38861M items_per_second=4.45776M/s
BM_ReadIntegers        1641 ms         1641 ms            1 items=8.38861M items_per_second=5.11252M/s
BM_ReadFloats          4173 ms         4172 ms            1 items=8.38861M items_per_second=2.01078M/s
BM_ReadBools           1898 ms         1898 ms            1 items=8.38861M items_per_second=4.4205M/s
```

## Caveats

### File Size

An .xlsx file is essentially a bunch of .xml files in a .zip archive.
Internally, OpenXLSX uses the miniz library to compress/decompress the
.zip archive, and it turns out that miniz has an upper limit regarding
the file sizes it can handle.

The maximum allowable file size for a file in an archive (i.e. en entry
in a .zip archive, not the archive itself) is 4 GB (uncompressed).
Usually, the largest file in an .xlsx file/archive, will be the .xml
files holding the worksheet data. I.e., the worksheet data may not
exceed 4 GB. What that translates to in terms of rows and columns depend
a lot on the type of data, but 1,048,576 rows x 128 columns filled with
4-digit integers will take up approx. 4 GB. The size of the compressed
archive also depends on the data held in the worksheet, as well as the
compression algorithm used, but a workbook with a single worksheet of 4
GB will usually have a compressed size of 300-350 MB.

The 4 GB limitation is only related to a single entry in an archive, not
the total archive size. That means that if an archive holds multiple
entries with a size of 4GB, miniz can still handle it. For OpenXLSX,
this means that a workbook with several large worksheets can still be
opened.

### Memory Usage

OpenXLSX uses the PugiXML library for parsing and manipulating .xml
files in .xlsx archive. PugiXML is a DOM parser, which reads the entire
.xml document into memory. That makes parsing and manipulation
incredibly fast.

However, all choices have consequences, and using a DOM parser can also
demand a lot of memory. For small spreadsheets, it shouldn't be a
problem, but if you need to manipulate large spreadsheets, you may need
a lot of memory.

The table below gives an indication of how many columns of data can be
handled by OpenXLSX (assuming 1,048,576 rows):

|           | Columns |
|:----------|:--------|
| 8 GB RAM  | 8-16    |
| 16 GB RAM | 32-64   |
| 32 GB RAM | 128-256 |

Your milage may vary. The performance of OpenXLSX will depend on the
type of data in the spreadsheet.

Note also that it is recommended to use OpenXLSX in 64-bit mode. While
it can easily be used in 32-bit mode, it can only access 4 GB of RAM,
which will severely limit the usefulness when handling large
spreadsheets.

If memory consumption is an issue for you, you can build the OpenXLSX
library in compact mode (look for the ENABLE_COMPACT_MODE in the
CMakeLists.txt file), which will enable PugiXML's compact mode. OpenXLSX
will then use less memory, but also run slower. See further details in
the PugiXML documentation
[here](https://pugixml.org/docs/manual.html#dom.memory.compact). A test
case run on Linux VM with 8 GB RAM revealed that OpenXLSX could handle a
worksheet with 1,048,576 rows x 32 columns in compact mode, versus
1,048,576 rows x 16 columns in default mode.

### Unicode

By far the most questions I get about OpenXLSX on Github, is related to Unicode.
It is apparently (and understandably) a source of great confusion for many people.

Early on, I decided that OpenXLSX should focus on the Excel part, and not be a 
text encoding/conversion utility also. Therefore, **all text input/output to 
OpenXLSX MUST be in UTF-8 encoding**... Otherwise it won't work as expected. 
It may also be necessary that the source code files are saved in UTF-8 format. 
If, for example, a source file is saved in UTF-16 format, then any string literals
will also be in UTF-16. So if you have any hard-coded string literals in your source
code, then the source file **must** also be saved in UTF-8 format.

All string manipulations and usage in OpenXLSX uses the C++ std::string,
which is encoding agnostic, but can easily be used for UTF-8 encoding.
Also, Excel uses UTF-8 encoding internally (actually, it might be
possible to use other encodings, but I'm not sure about that).

For the above reason, **if you work with other text encodings, you have
to convert to/from UTF-8 yourself**. There are a number of options (e.g.
Boost.Nowide or Boost.Text). Internally, OpenXLSX uses Boost.Nowide; it has a number
of handy features for opening files and converting between std::string and std::wstring
etc. I will also suggest that you watch James McNellis' presentation at [CppCon 2014](https://youtu.be/n0GK-9f4dl8),
and read [Joel Spolsky's blog](https://www.joelonsoftware.com/2003/10/08/the-absolute-minimum-every-software-developer-absolutely-positively-must-know-about-unicode-and-character-sets-no-excuses/).

Unicode on Windows is particularly challenging. While UTF-8 is well 
supported on Linux and MacOS, support on Windows is more limited. For example, 
output of non-ASCII characters (e.g. Chinese or Japanese characters) to the 
terminal window will look like gibberish. As mentioned, sometimes you also have to be mindful 
of the text encoding of the source files themselves. Some users have had problems
with OpenXLSX crashing when opening/creating .xlsx files with non-ASCII 
filenames, where it turned out that the ***source code*** for the test program
was in a non-UTF-8 encoding, and hence the input string to OpenXLSX was also
non-UTF-8. To stay sane, I recommend that source code files are always 
in UTF-8 files; all IDE's I know of can handle source code files in UTF-8 
encoding. Welcome to the wonderful world of unicode on Windows 🤮

### Zip Library
An Excel-file is essentially just a bunch of .xml files wrapped in a .zip archive. OpenXLSX uses a 3rd party library to extract the .xml files from the .zip archive. The default library used by OpenXLSX is Zippy, which is an object-oriented wrapper around miniz. The miniz library is fast, and is header-only, which is ideal for OpenXLSX.

However, it is possible to use a different zip-library, if you want to. In rare cases, you may experience stability issues with miniz. In those cases, it may be useful to try a different zip-library.

Using the Zippy/miniz library requires no special efforts; it will work straight out of the box. Using a different zip-library, however, will require some work.

In order to use a different zip-library, you must create a wrapper class that conforms to the interface specified by the IZipArchive class. Note that this is implemented using *type erasure*, meaning that no inheritance is required; the class just needs to have a conforming interface, thats all. After that, provide an object of the class and supply it to the OpenXLSX constructor.

To see an example of how this is done, take a look at Demo1A in the Examples folder. This example uses a class called CustomZip (using libzip as the zip library) which can be found under Examples/external/CustomZip. In order to build the example program, make sure that libzip (and its dependencies) is installed on your computer, and enable the OPENXLSX_ENABLE_LIBZIP_EXAMPLE option in the CMakeLists.txt file in the OpenXLSX root.

As mentioned, the Demo1A example program uses libzip. libzip is a very stable library and widely used. However, my experience is that it is quite slow for large zip files, such as large spreadsheets. For that reason, libzip may not be the ideal solution, but it is useful for showing how a different zip library can be used.

<h2 id="reference-guide">Reference Guide (to be written)</h2>
This section remains to be written

## Example Programs

In the 'Examples' folder, you will find several example programs, that illustrates how to use OpenXLSX. Studying 
those example programs is the best way to learn how to use OpenXLSX. The example programs are annotated, so it 
should be relatively easy to understand what's going on.

## Changes

### New in version 0.5.x
OpenXLSX now pulls in dependencies either from the operating system (if installed) or directly from the upstream source repositories.

### New in version 0.4.x
OpenXLSX can now use other zip libraries than the default Zippy/miniz library. See Demo1A as an example of how it's done

### New in version 0.3.x
This version includes row ranges and iterators. It also support assignment of containers of cell values to XLRow 
objects. This is significantly faster (up to x2) than using cell ranges or accessing cells by cell references.

### New in version 0.2.x

The internal architecture of OpenXLSX has been significantly re-designed
since the previous version. The reason is that the library was turning
into a big ball of mud, and it was increasingly difficult to add
features and fix bugs. With the new architecture, it will (hopefully) be
easier to manage and to add new features.

Due to the re-design of the architecture, there are a few changes to the
public interface. These changes, however, are not significant, and it
should be easy to update:

* All internal objects are now handled as values rather than pointers,
  similar to the approach taken in the underlying PugiXML library. This
  means that when requesting a certain worksheet from a workbook, the
  resulting worksheet is not returned as a pointer, but as an object
  that supports both copying and moving.
* The distinction between interface objects and implementation objects
  are now gone, as it made it very difficult to manage changes. It was
  an attempt to implement the pimpl idiom, but it wasn't very effective.
  In the future, I may try to implement pimpl again, but only if it can
  be done in a simpler way.
* All member functions have been renamed to begin with a small letter
  (camelCase), i.e. the member function WorksheetCount() is renamed to
  worksheetCount(). This was done mostly for cosmetic reasons.

I realise that these changes may cause problems for some users. Because
of that, the previous version of OpenXLSX can be found in the "legacy"
branch of this repository. However, I strongly recommend that you
transition to the new version instead.

<h2 id="detailed-change-log">Detailed change log</h2>

### (aral-matrix) 17 March 2026 - Install package config files for libzip and pugixml if they are installed with OpenXLSX
* when the dependencies are pulled in from source repositories, their package config files will be installed alongside OpenXLSX
* `XLZipArchive.hpp` provides two new functions `const char *OpenXLSX::ZipLibraryName()` and `const char *OpenXLSX::ZipLibraryVersion()` for the user to obtain info about the zip library in use. *NOTE*: These do not reflect information about a custom zip implementation such as used in `Demo1A.cpp`
* `OpenXLSX` and dependencies are installed into `/usr/local/lib/OpenXLSX` subfolder to avoid version conflicts for parallel installations of zip library (`miniz` or `libzip`), `pugixml`, `nowide`
* `pugixml` and `libzip` package config (`.pc`) files are now part of the installation (`miniz` package config was already installed before if needed)
* dependency package config files installed by OpenXLSX will be installed as `pugixml-OpenXLSX.pc`, `libzip-OpenXLSX.pc`, `miniz-OpenXLSX.pc` respectively to avoid conflicts
* dependency package config files should behave well with existing versions of the dependencies (OpenXLSX package config file gives precedence to the self-installed dependencies)
* OpenXLSX package config file now provides the runtime path for an executable linked against OpenXLSX shared libraries in `/usr/local/lib/OpenXLSX`

### (aral-matrix) 16 March 2026 - Dynamically pull in dependencies from external sources (operating system or code repository)
* upped OpenXLSX library version to `0.5.0`
* static & dynamic build: all dependencies are now linked in dynamically depending on the project configuration from available / allowed sources, which can be the OS or code repositories

### (aral-matrix) 25 December 2025 - Fix for issue #382: XLWorksheet::range() bounds check without exception
* added a check for an empty worksheet in `XLWorksheet::range()` to prevent an exception raised from `XLCellReference` constructor

### (aral-matrix) 09 October 2025 - Work in progress: CPack configuration for a debian package
* added `cmake/get-git-HEAD-ID.cmake` and `cmake/libopenxlsxCPackOptions.cmake.in`
* `CMakeLists.txt`: `CPack` configuration is generated and can be invoked with `cpack -G DEB` - *CAUTION*: the debian package will most likely not function at this stage due to missing dependencies
* TBD how to invoke package generation directly from CMake
* TODO: correctly identify the dependencies (pugixml, libzip, nowide) for CPack

### (aral-matrix) 10 September 2025 - implemented support for libzip installation from github repo (to be tested on Windows)
* `OPENXLSX_ENABLE_LIBZIP=ON` now works with `OPENXLSX_CPM_LOCAL_PACKAGES_ONLY=OFF` - pending confirmation of a test on Windows

### (aral-matrix) 28 August 2025 - implemented reverse iteration over row ranges
* new class `XLRowReverseIterator` (XLRow.hpp)
* implemented `XLRowRange::rbegin()` and `XLRowRange::rend()` to reverse-iterate over a row range
* new templated class `XLReverseRange` (XLIterator.hpp) to reverse a range of class T that exposes ```T::rbegin()``` and ```T::rend()``` and typedef ```T::reverse_iterator```
* using `XLReverseRange`, range-based reverse iteration is demonstrated in `Examples/Demo6.cpp`, Example usage: `for (auto& row : XLReverseRange(wks.rows(firstRow, lastRow)))`
* currently, only XLRowRange supports reverse iteration

### (aral-matrix) 27 August 2025 - finalized code review after hiding `pugixml` headers from the library interface
* finished removing default constructors, destructors and assignment operators from XLStyles header files

### (aral-matrix) 26 August 2025 - added a library pkg-config (.pc) file, also added option for building a static bundled library file
* CMake build configuration now also creates & installs `pkg-config` files that can be used as demonstrated in the new `Scripts/compile.sh`
* build option `OPENXLSX_BUNDLED_STATIC_LIB` will now create `libOpenXLSX-bundled.a` library file that is not installed, but can be linked against while including all dependencies (only works with `BUILD_SHARED_LIBS=OFF`, and `OPENXLSX_CPM_LOCAL_PACKAGES_ONLY=OFF` or all dependencies available as static libraries on the build system). This uses the newly added `OpenXLSX/bundle_static_library.cmake` (under MIT License, Copyright (c) 2019 Cristian Adam).
* re-enabled the `Makefile.GNU`, but until full support for options is back, this Makefile is overriding some options to the only supported configurations
* removed some obsolete (and commented-out) code from the various CMakeFiles.txt

### (aral-matrix) 16 August 2025 - dropped `external` source code from repository, refined cmake configuration
* implemented changes from @troldal to drop external source code
* as a result, `Makefile.GNU` is currently non-functional!
* cmake build options are now (some renamed, some removed, new `OPENXLSX_CPM_LOCAL_PACKAGES_ONLY`):
  * option(OPENXLSX_CREATE_DOCS           "Build library documentation (requires Doxygen and Graphviz/Dot to be installed)" ON)
  * option(OPENXLSX_BUILD_SAMPLES         "Build sample programs" ON)
  * option(OPENXLSX_BUILD_TESTS           "Build and run library tests" ON) # TBD: are these still functional?
  * option(OPENXLSX_BUILD_BENCHMARKS      "Build and run library benchmarks" OFF)
  * option(OPENXLSX_ENABLE_LIBZIP         "Enable using libzip" OFF) # when OFF, default zip library is miniz. NOTE: libzip currently does NOT support CPM_DOWNLOAD_ALL
  * option(OPENXLSX_FORCE_NOWIDE          "Force use of boost nowide, even on non-Windows systems (testing)" OFF)
  * option(OPENXLSX_ENABLE_LIBZIP_EXAMPLE "Build Demo1A example using libzip - requires libbz2-dev" OFF)
  * option(         BUILD_SHARED_LIBS     "Builds the shared library" OFF) # replaced OPENXLSX_SHARED_LIBRARY with cmake option reserved for that purpose
  * option(OPENXLSX_COMPACT_MODE          "Build library in compact mode (slower, but uses less memory)" OFF)
  * option(OPENXLSX_CPM_LOCAL_PACKAGES_ONLY "CPM shall only use packages already installed on the host OS, otherwise fail" OFF)
* minor code refactoring to work with different library interfaces depending on package source (different include paths, different namespaces)

### (aral-matrix) 31 July 2025 - added use of cmake `find_package` for `LibZip` and `PugiXML`
* `OpenXLSX/CMakeLists.txt`: added `find_package` for `LibZip` and `PugiXML`. Unfortunately, for `LibZip`, this generates an error unless the unneeded components `zipcmp`, `zipmerge` & `ziptool` are also installed on the system. TBD how to ignore those missing.

### (aral-matrix) 30 July 2025 - enabled compilation against ```nowide``` installed on the operating system
* added to cmake and GNU make: option `OPENXLSX_FORCE_NOWIDE` - set to `ON` to use force the use of `nowide` even on non-Windows systems (this flag is for testing purposes)
* added to cmake and GNU make: option `OPENXLSX_ENABLE_LIBBOOST_NOWIDE` - set to `ON` to use `nowide` from an installed `libboost`
* adjustments to accommodate system library `boost nowide` (include path starts with `boost/` and namespace is `boost::nowide` vs. `nowide`)
* minor bugfixes: missing `#include <memory>` in `XLZipArchive.hpp`, `#include <stdexcept>` in `detail/LibZip.hpp`
* added `Demo1A` to `Makefile.GNU`
* added output of `nowide` status to `Demo4`

### (aral-matrix) 21 July 2025 - included nowide support in ```OpenXLSXFileSystemTools```, cleaned up cmake and GNU make options
* BUGFIX ```Examples/CMakeLists.txt``` for Demo4 (to be tested): correctly add ```external/nowide``` to the include path
* BUGFIX ```Examples/CMakeLists.txt``` for Demo1A (to be tested): correctly add ```external/nowide``` to the include path
* updated ```Demo1A``` CustomZip implementation to fit the modified ```IZipArchive``` concept
* added to cmake and GNU make: option ```OPENXLSX_ENABLE_LIBPUGIXML``` - set to ```ON``` to use an installed ```libpugixml```
* added to GNU make: (already existed in cmake) option ```OPENXLSX_ENABLE_LIBZIP``` - set to ```ON``` to use an installed ```libzip```
* added to cmake: option ```OPENXLSX_SHARED_LIBRARY``` - set to ```ON``` for shared library build, ```OFF``` builds the static library
* added to GNU make: option stub (unsupported for now) ```OPENXLSX_SHARED_LIBRARY```

### (aral-matrix) 20 July 2025 - enabled compilation against ```libpugixml``` installed on the operating system
* hid ```XLXmlParser``` from public OpenXLSX API - this should address conflicts with ```pugixml.hpp``` headers available elsewhere
* enabled compilation against ```libpugixml``` - for cmake, variable is ```OPENXLSX_ENABLE_LIBPUGIXML```, in Makefile.GNU, variable is ```USE_LIBPUGIXML``` - set to yes if system installed library shall be used
* upped the OpenXLSX version tag to 0.4.2

### (aral-matrix) 14 July 2025 - minor bugfixes & a test of signed commits
* addressed issue https://github.com/troldal/OpenXLSX/issues/368
* configured commit signature for a development machine

### (aral-matrix) 04 May 2025 - moved file system access functions (shared by zip implementations and XLDocument) to detail/OpenXLSXFileSystemTools.hpp
* in preparation for localizing (if not removing) the boost::nowide dependency, the new header file ```detail/OpenXLSXFileSystemTools.hpp``` now comprises all functions where unicode (filename) support might be relevant, to be implemented centrally - currently on the To-Do list
* ```XLDocument::create```: creating a new document no longer creates a file under that name until an explicit call of ```XLDocument::save``` or ```::saveAs```. This is to remove a dependency of XLDocument on boost::nowide on Windows.

### (aral-matrix) 01 May 2025 - replaced zippy implementation with the underlying miniz library (cmake) and added support for libzip (cmake, GNU make)
* @troldal replaced the zippy implementation with a smaller zippy-wrapper for the actual dependency, the miniz library, and added the cmake support for automatically pulling in the dependency from the miniz repository
* ```OpenXLSX/headers/detail/```: new headers ```LipZip.hpp``` (libzip wrapper) and ```Zippy.hpp``` (miniz wrapper)
* ```CMakeLists.txt```: Option ```OPENXLSX_ENABLE_LIBZIP``` activates libzip use, disabling the option defaults to the miniz / Zippy wrapper
* ```CMakeLists.txt```: Option ```OPENXLSX_ENABLE_LIBZIP_EXAMPLE``` replaces the prior use of OPENXLSX_ENABLE_LIBZIP for ```Demo1A```
* API remains unchanged
* fixes for old pull requests https://github.com/troldal/OpenXLSX/pull/191 (AmigaOS paths) and https://github.com/troldal/OpenXLSX/pull/210 (Windows style paths) have been incorporated into both zip library wrapper classes
* **CAUTION**: for the libzip implementation, there is still a minor unresolved conflict when modifying archives created with other tools / prior versions of OpenXLSX (or the miniz version): The resulting archive's general purpose flag bits will not be set to UTF-8 when the flag is set for individual files. This works fine with LibreOffice, but ```unzip``` complains about the flag mismatch. *This issue is on my to-to list.*

### (aral-matrix) 20 April 2025 - added validation of worksheet names when creating, renaming or cloning worksheets to address #358
* added ```bool XLDocument::validateSheetName(std::string sheetName, bool throwOnInvalid = false)``` - can be called by the user to test whether a name would throw
* if ```XLSheet::setName```, ```XLWorkbook.addWorksheet``` or ```XLWorkbook.cloneSheet``` are invoked with a name for which ```validateSheetName``` would return false, an ```XLInputError``` is thrown with the validation rule that was violated.
* this change addresses https://github.com/troldal/OpenXLSX/issues/358

**CAUTION**: this change is potentially code-breaking as it can throw an exception on code that previously executed without errors - However, when it throws, previous versions would have produced a workbook that Excel refuses to read.

### (aral-matrix) 12 April 2025 - added cmake option(OPENXLSX_ENABLE_LTO "Enables Link-Time Optimization (LTO)" ON)
* merged pull request https://github.com/troldal/OpenXLSX/pull/355 adding the cmake option ```OPENXLSX_ENABLE_LTO``` that permits disabling link-time optimization altogether. It remains ```ON``` by default.

### (aral-matrix) 08 April 2025 - XLMergeCells: remove <mergeCells> element from worksheet XML when merge count is 0 - addresses #351
* ```XLMergeCells``` is now constructed with the worksheet root XML node (unfortunately necessary) and will use this access to create/delete the <mergeCells> node as necessary, this addresses https://github.com/troldal/OpenXLSX/issues/351
* added a function ```XLMergeCells::deleteAll``` to clear all merges in the worksheet
* added a typedef ```XLMergeIndex``` as the parameter / return type for all functions using a merge index - the underlying ```int32_t``` remains unchanged
* added a ```constexpr const XLMergeIndex XLMergeNotFound = -1``` for code readability

### (aral-matrix) 07 April 2025 - Demo10: added a disabled use of borders with merged cells
* enable Demo10 line 450 to experiment - but LibreOffice behaves weird (at least) with (diagonal) borders, so I have disabled this Demo functionality by default

### (aral-matrix) 24 March 2025 - XLStyles: XLFont fix attribute values underline, scheme, vertAlign
* getters ```XLFont::underline, ::scheme, ::vertAlign```: fix default value to set for attribute val when tag doesn't exist
* setter ```XLFont::setUnderline```: return correct "none" value for XLUnderlineNone from XLUnderlineStyleToString (was returning empty string)

### (aral-matrix) 23 March 2025 - XLStyles: get bool settings when omitted attribute shall default to true - addresses #347
* added function ```getBoolAttributeWhenOmittedMeansTrue``` to ```XLUtilities```
* ```XLStyles``` ```XLFont```: changed bool getter functions to return ```true``` when tag exists, but attribute ```val``` is omitted, to be in line with OOXML spec. This addresses https://github.com/troldal/OpenXLSX/issues/347. Affected getters: ```bold()```, ```italic()```, ```strikethrough()```, ```outline()```, ```shadow()```, ```condense()```, ```extend()```

### (aral-matrix) 16 March 2025 - XLSheet::findCell added to address #333, setting an XLFormula to an empty string now deletes the formula
* added function(s) ```XLSheet::findCell``` that allow to try and fetch a cell without creating the row/cell XML (like the non-creating XLCellIterator). This function complements ```XLSheet::cell``` (which always creates the XML cell node and returns a valid object)
* after using ```findCell```, the returned ```XLCellAssignable::empty()``` method must be checked to ensure success before accessing any cell properties
* ```XLSheet::findCell``` provides a solution to https://github.com/troldal/OpenXLSX/issues/333, a demonstration of this solution has been added to ```Demo1.cpp```
* setting ```XLFormula``` to an empty (zero-length) string will now delete the formula XML node from the cell without further actions

### (aral-matrix) 16 March 2025 XLSheet: fixed issue #338 - align cmake_minimum_required to be VERSION 3.15 everywhere
* in response to https://github.com/troldal/OpenXLSX/issues/338, updated all occurrences of ```CMakeLists.txt``` in ```Examples/external/nowide/*``` to have cmake_minimum_required VERSION 3.15

### (aral-matrix) 15 March 2025 XLSheet: fixed issue #337 - assign tabSelected value with newly created attribute if it didn't exist
* in response to https://github.com/troldal/OpenXLSX/issues/337, added a forgotten assignment to ```XLSheet.cpp```

### (aral-matrix) 17 February 2025 added some comments to XLSheet class definition to clarify that the sheet index is 1-based (issue #332)
* in response to https://github.com/troldal/OpenXLSX/issues/332, added (doxygen) documentation to ```XLSheet.hpp``` clarifying that sheet index is 1-based

### (aral-matrix) 14 February 2025 Added cctype includes to XLSheet and XLDrawing, resolving issue #330
* in response to https://github.com/troldal/OpenXLSX/issues/330, added ```#include <cctype>``` to ```XLSheet.cpp``` and ```XLDrawing.cpp```

### (aral-matrix) 05 February 2025 - XLDocument patch to address issue #279 about conflicting stat / _stat definitions
* XLDocument is now using custom names (```STAT```, ```STATSTRUCT```) to link to the platform specific implementation of ```stat``` without naming conflicts

### (aral-matrix) 03 February 2025 - XLComments and shared strings cleanup

Before I start working on the next items on my to-do list (tables/filters, hyperlink support), I am merging all recent patches into master. I have not yet had much feedback on whether the changes work with MS Office, but I am confident that if you discover any issues, I can fix them quickly.

Should you experience stability issues, please revert to commit https://github.com/troldal/OpenXLSX/commit/4ed9c97ad613526bf1544296acd24639dcbe2846 and submit a bug report.

***New features***
* support for creating / reading / modifying / deleting comments is now implemented in ```XLComments``` -> see ```Demo1.cpp```
* using an ```XLRowIterator``` no longer creates the XML for rows that do not exist until the iterator is dereferenced
* ```XLDocument::cleanupSharedStrings()``` can now be called manually to rewrite the shared strings cache (and remove all strings that are no longer referenced from any cell)

### (aral-matrix) 02 February 2025 - Support for cleaning up shared strings (issue #193), XLRowIterator no longer creates missing rows unless iterator is dereferenced
* ```XLDocument``` now has a member function ```void cleanupSharedStrings()``` that will reindex shared strings for the complete workbook and remove all shared strings that are no longer referenced anywhere, or that have been set to the empty string. This addresses https://github.com/troldal/OpenXLSX/issues/193.
* Added support for non-creating ```XLRowIterator```: can now iterate over a range of rows and test ```bool XLRowIterator::rowExists()``` before accessing it. This allows to skip non-existing rows without creating them. Functionality is analogous to ```XLCellIterator``` and ```bool XLCellIterator::cellExists()```
* Accordingly, fetching an ```XLWorksheet::range(..)``` will no longer create all missing rows in the range
* Added to ```XLCellValueProxy``` two functions to manipulate shared string indexes directly, bypassing ```XLSharedStrings```:
    * private: ```int32_t stringIndex() const```
    * private: ```bool setStringIndex(int32_t newIndex)```
* Added to ```XLSharedStrings```:
    * public: ```int32_t stringCount() const``` - returns the amount of strings currently in the shared strings cache
    * protected: ```int32_t rewriteXmlFromCache()``` - called from ```XLDocument::cleanupSharedStrings``` - triggers a full wipe of the shared strings XML & re-creation from the string cache. Returns the number of shared strings written to XML
* Added to ```XLRowIterator```:
    * public: ```bool rowExists()``` - test whether the ```XLRowIterator``` currently points to a row that already exists in the XML
    * public: ```bool endReached()``` - equivalent to (XLRowIterator) it == (XLRowRange) range.end()
    * public: ```uint32_t rowNumber() const``` - return the current row that the iterator is pointing to (m_lastRow + 1 if endReached() == true)
* added to ```XLRow```:
    * public: ```bool empty() const``` returns true if the ```XLRow``` instance is not linked to valid XML
    * public: ```explicit operator bool() const``` the opposite of ```empty()```
* added a missing include of ```XLCellRange.hpp``` to ```XLSheet.hpp```

### (aral-matrix) 31 January 2025 - Support for XLWorksheet comments mostly complete - still in testing stage
* for that, implemented a new XLContentType::Relationship
* removed a redundant ```XLContentTypeToString``` function from ```XLContentTypes.cpp```, as a function ```XLContentTypeString``` already exists in ```utilities/XLUtilities.hpp```
* implemented XLComment class and the possibility to iterate over only *existing* comments in a worksheet (see ```Examples/Demo1.cpp```) as they appear in the underlying XML. This is much more practical when searching for comments in a worksheet created by another application.
* proper "load upon access" for worksheet dependencies, so that worksheet relationships, comments, table and vmlDrawing files will not be loaded into the XMLDocument managed objects unless actually accessed by the user. The files will still remain unchanged in the archive if not accessed.
* ```Override``` entries for the worksheet dependencies (comments, vmlDrawing, table) in ```[Content Types].xml```

### (aral-matrix) 17 January 2025 - Basic support for comments is implemented - testing stage
The support for comments is now in a stage where it can be used - please refer to Demo1 line 124ff for a quick "howto".
This feature is still in alpha stage, with a few open TBDs:
* the library currently assumes that comment entries are well sorted, first by row, then by column - if this is not the case, existing comments might not be readable / be found
* the VML Drawing support is basic at best, for lack of documentation. I have made most features available through ```XLShape XLComments::shape(std::string const& cellRef)``` - for methods of XLShape please refer to the ```XLDrawing``` header file
* missing support in XLShape for now:
```
    // XLShapeShadow& shadow();          // v:shape subnode v:shadow
    // XLShapeFill& fill();              // v:shape subnode v:fill
    // XLShapeStroke& stroke();          // v:shape subnode v:stroke
    // XLShapePath& path();              // v:shape subnode v:path
    // XLShapeTextbox& textbox();        // v:shape subnode v:textbox
```
* missing: library still needs to add ```Override``` entries for the worksheet dependencies (comments, vmlDrawing, table)
* to be replaced with proper logic: library (XLDocument) currently loads worksheets dependencies in a workaround

### (aral-matrix) 13 January 2025 BUGFIX XLSheetBase::index() / XLDocument::execQuery: implemented XLQueryType::QuerySheetIndex
* as the title says - the XLQueryType::QuerySheetIndex query implementation was missing from XLDocument::execQuery, meaning XLSheetBase::index() would either throw or return nonsense - today's patch finally implemented the function

### (aral-matrix) 10 January 2025 deletion of worksheet rows from OOXML, bugfix for XLCellValue(Proxy)::get
* added bool XLWorksheet::deleteRow(uint32_t rowNumber) - can be used to eliminate rows from OOXML - no renumbering of rows behind is performed, the row entry is simply removed from OOXML, this addresses https://github.com/troldal/OpenXLSX/issues/156
* templated getter T XLCellValue(Proxy)::get() now uses a workaround (due to undefined behavior) when getting a temporary string_view or (const) char * - this functionality was only safe when called with a persistent XLCellValue(Proxy) variable - users should not use this template to fetch a string reference type as it may be removed in the future
* introduced ```XLKeepCellValue::privateGet``` as a library internal that can be used with the old behavior for performance reasons, from functions that can guarantee the validity of the XLCellValue for the duration of access to the string reference
* in line with the change to the templated getter, the ```std::ostream& operator<<```for XLCellValue and XLCellValueProxy now fetch string types as ```std::string```, this addresses https://github.com/troldal/OpenXLSX/issues/166

### (aral-matrix) 10 January 2025 - bugfixes to XLDateTime, implicit conversion to double for integer, bool cell values
* XLDateTime::tm() BUGFIX: added overflow handling in rounded seconds at the end of a minute to address https://github.com/troldal/OpenXLSX/issues/138
* XLDateTime::tm() BUGFIX: account for fractions (time of day) in loops counting year & month
* XLDateTime::tm() precaution: added safeguards against infinite loops counting year & month
* XLCellValue: added implicit conversion from integer & bool for ```XLCellValue::get<double>()``` and ```XLCellValue::get<XLDateTime>()```. Note: implicit conversion from string is available in ```VisitXLCellValueTypeToDouble```, but disabled (forced throw)

### (aral-matrix) 09 January 2025 - Support for XLWorksheet protection
* fixed some missing symbol exports when building the shared library - this addresses https://github.com/troldal/OpenXLSX/issues/316.
* ensured that utility functions get exported to shared library build: ```XLCfTypeFromString```, ```XLCfTypeToString```, ```XLCfOperatorFromString```, ```XLCfOperatorToString```, ```XLCfTimePeriodFromString```, ```XLCfTimePeriodToString```
* BUGFIX XLSheet: added ```XLSheet::isActive``` and ```XLSheet::setActive``` function definitions to ensure bug-free export of symbols to shared library - this addresses https://github.com/troldal/OpenXLSX/issues/316 - please do not ask me why this was never a problem for the static build, I am simply not smart enough to understand that :P
* BUGFIX XLDocument: added explicit OPENXLSX_EXPORT macro to new global utility functions ```BinaryAsHexString```, ```ExcelPasswordHash```, ```ExcelPasswordHashAsString``` so that they are also exported when the shared library is being built
* added XLWorksheet protection settings demo to Demo1
* added ```ExcelPasswordHash``` and ```ExcelPasswordHashAsString``` to XLDocument as global utility functions
* made ```BinaryAsHexString``` a global utility function so that XLWorksheet can use them as well
* moved functions ```hexDigit``` and ```BinaryAsHexString``` from XLRelationships to XLDocument
* added sheet protection & password (hash) functionality to XLWorksheet (exclusive, not for XLChartsheet) - see Demo1 for usage. This addresses https://github.com/troldal/OpenXLSX/issues/311
    * setter functions:
        * ```bool protectSheet(bool set = true)```
        * ```bool protectObjects(bool set = true)```
        * ```bool protectScenarios(bool set = true)```
        * ```bool allowInsertColumns(bool set = true)```
        * ```bool allowInsertRows(bool set = true)```
        * ```bool allowDeleteColumns(bool set = true)```
        * ```bool allowDeleteRows(bool set = true)```
        * ```bool allowSelectLockedCells(bool set = true)```
        * ```bool allowSelectUnlockedCells(bool set = true)```
        * ```bool denyInsertColumns()```
        * ```bool denyInsertRows()```
        * ```bool denyDeleteColumns()```
        * ```bool denyDeleteRows()```
        * ```bool denySelectLockedCells()```
        * ```bool denySelectUnlockedCells()```
        * ```bool setPasswordHash(std::string hash)```
        * ```bool setPassword(std::string password)```
        * ```bool clearPassword()```
        * ```bool clearSheetProtection()```
    * getter functions:
        * ```bool sheetProtected()```
        * ```bool objectsProtected()```
        * ```bool scenariosProtected()```
        * ```bool insertColumnsAllowed()```
        * ```bool insertRowsAllowed()```
        * ```bool deleteColumnsAllowed()```
        * ```bool deleteRowsAllowed()```
        * ```bool selectLockedCellsAllowed()```
        * ```bool selectUnlockedCellsAllowed()```
        * ```std::string passwordHash()```
        * ```bool passwordIsSet()```
* added ```std::string XLWorksheet::sheetProtectionSummary()``` for easy control of established settings

### (aral-matrix) 08 January 2025 - Support for XLWorksheet conditional formatting (experimental)
This is a major patch to address https://github.com/troldal/OpenXLSX/issues/315 - conditional formatting is now implemented in an experimental stage.
* XLWorksheet: added support for conditional formatting (rules)
* XLStyles: added differential cell formats (dxfs) support required by conditional formatting
* moved class ```XLUnsupportedElement``` from XLStyles to XLXmlFile header, so that XLWorksheet can use it for conditional formatting functionality
* XLChartSheet: added ```bool isActive_impl()``` and ```bool setActive_impl()``` as no-op function stubs in the hopes this resolves https://github.com/troldal/OpenXLSX/issues/316

***experimental*** in this case means:
* users are kindly requested to verify that the generated OOXML behaves well with MS Office (I can't promise yet I got the node order right for all scenarios)
* it appears that the <cfRule><formula> may appear up to 3 times per cfRule - the current implementation only supports a single entry for <formula>
* as the conditional formatting uses differential formats, and I am re-using XLStyles classes, there is currently an automatism that by accessing a format property, that property node gets created if it does not yet exist. For differential formats, this is undesired when testing whether a given setting exists. I have yet to implement something along the lines of ```bool settingExists(std::string settingName)```
* I have implemented boolean values to be stored in XML as ```"true"``` and ```"false"``` - whereas LibreOffice appears to store them (for cfRules) as ```1``` and ```0```). The reason is: I want to know if this works, and if it does, stay consistent in how OpenXLSX stores boolean values. I may have to modify this as I learn more
* Another boolean "gotcha": I do not yet know how MS Office evalutes attribute names that exist with an empty value, e.g. ```aboveAverage=""``` when for ```aboveAverage```, the documentation defines ```true``` as the default - does that mean an empty string gets evaluted as ```true```?

### (aral-matrix) 30 December 2024 - removed ```XLWorkbook::sharedStrings``` and ```XLWorkbook::hasSharedStrings```
* removed these (pointless) functions in the hopes that no one was using them - please report an issue if this causes a problem for you - if you can change the access method, ```XLDocument::sharedStrings()``` returns the same, and ```hasSharedStrings``` was always returning true anyways.

### (aral-matrix) 30 December 2024 - XLSharedStrings passed as const reference everywhere, stored in std::reference_wrapper
* this is a library internal patch that avoids constructing (& destroying) a new XLSharedStrings instance for every row/cell access

### (aral-matrix) 29 December 2024 - XLXmlFile and derived classes: undid 2024-12-20 addition of xmlName() function
* this was a function mainly foreseen for debugging purposes, but not serving any practical purpose, it was removed again

### (aral-matrix) 25 December 2024 - XLStyles: fixed implementation of ```strike```(through) font property to address issue #314
* XLStyles: if the attribute ```val``` is omitted in the ```<strike>``` XML tag, the value is now interpreted as ```true``` as described in the format specification - previously this was wrongly interpreted as "strikethrough is not set". This addresses issue https://github.com/troldal/OpenXLSX/issues/314

### (aral-matrix) 23 December 2024 - XLStyles, XLSheet, XLUtilities: moved XML node insertion functions to XLUtilities, introduced m_nodeOrder in XLSheet for ordered insert of root nodes
* XLSheet now also uses the ordered insert functionality added on 2024-12-19. Required functions were moved from XLStyles to XLUtilities.

### (aral-matrix) 20 December 2024 - XLXmlFile and derived classes (XLWorksheet!) now expose a ::valid() method
* addressed https://github.com/troldal/OpenXLSX/issues/312 on a lower level, all classes derived from XLXmlFile now have a bool valid() method that will return true if a non-nullptr XML data block is linked to the class. For the user, this mostly matters in XLWorksheet, XLWorkbook & XLStyles
* while addressing issue #312, implemented explicit copy/move constructors and assignment operators for XLStyles, which should also address https://github.com/troldal/OpenXLSX/issues/310

### (aral-matrix) 19 December 2024 - XLStyles enhancement to address issues #304 and #305 - artificial ordering of XML elements
* In order to address https://github.com/troldal/OpenXLSX/issues/304 and https://github.com/troldal/OpenXLSX/issues/305, some XLStyles classes now support a strict predefined XML element node order

### (aral-matrix) 18 December 2024 - Bugfix for Issue #283 - shared strings cache was not cleared upon XLDocument::Close
* BUGFIX XLDocument::close: shared strings cache is now being cleared on doc close, this addresses issue https://github.com/troldal/OpenXLSX/issues/283
* zippy.hpp minor bugfix in ZipArchive::Close: m_IsOpen was not set to false
* Demo10: improved borders demo
* XLStyles: XLDataBarColor::setTheme now supports parameter ```XLDeleteProperty == XLInvalidUInt32 == 0xffffffff``` to delete the theme attribute from XML. This was necessary because even an empty ```theme=""``` attribute affects formatting.
* XLStyles appendAndGetAttribute / appendAndSetAttribute: removed a redundant check for ```not node.empty()```

### (aral-matrix) 17 December 2024 - Added exemplary use of XLBorder to Examples/Demo10.cpp
* in response to https://github.com/troldal/OpenXLSX/issues/309, added use of XLBorder to Demo10

### (aral-matrix) 15 December 2024 - Bugfix for Issues 306 and #297, default-disable XLDocument & XLStyles warnings about unsupported tags (#296)

* BUGFIX: document relationships in ```xl/_rels/workbook.xml.rels``` should again open without errors for both relative (to ```xl/``` folder) and absolute archive paths
* warnings about unsupported archive contents and styles elements are now disabled by default and can be enabled using XLDocument::showWarnings() prior to opening an XLSX file

### (aral-matrix) 09 December 2024 - Bugfix for XLDateTime (hopefully final ;)

Reviewed the XLDateTime code in response to https://github.com/troldal/OpenXLSX/issues/299 and fixed a bug that I think I may have introduced myself. Apologies, dates should now correctly construct from ```double```, ```struct tm``` and ```time_t``` and convert back to ```struct tm```.

### (aral-matrix) 27 October 2024 - Bugfix for XLSheet::mergeCells

It appears that MS Office does not tolerate any formatting XML nodes prior to the ```<mergeCells>``` XML node - in order to get rid of an according error message, the latest commit modifies the ```XLSheet::merges``` function to insert a newly created ```<mergeCells>``` node directly after the ```<sheetData>``` node.

### (aral-matrix) 25 October 2024 - Added default values to a newly created XLCellFormat (from XLCellFormats::create, when no template is provided)

These missing defaults could lead to followup errors when any style index of this cell was later assumed valid to access said style by index (Exception if the index was not in a valid range). All style indexes available in a cell format are now zero-initialized (with no assumptions what the style with index 0 may be configured as, normally it's defaults - if you want to be sure, provide a cell with a known format as copyFrom template to XLCellFormats::create).

### (aral-matrix) 14 October 2024 - added basic support to suppress harmless warnings (e.g. about XLSX unsupported features)
* ```XLDocument.hpp```: added ```showWarnings()``` (default setting) and ```suppressWarnings()```
* ```XLStyles.hpp```: added ```suppressWarnings``` parameter to constructor (default: ```false```)
* ```XLDocument::open```: if ```suppressWarnings()``` was called, suppress warnings about ignored comment xml files and unhandled workbook items
* ```XLDocument::open```: ```m_suppressWarnings``` setting is forwarded to XLStyles constructor

### (aral-matrix) 02 October 2024 - Issue #278 - missing include statement in XLException
* ```XLException.hpp```: added missing ```#include <string>```

### (aral-matrix) 30 September 2024 - Pull request #185 - create workbook relationship in _rels/.rels if missing
* ```XLDocument::open``` will create a missing workbook relationship in ```_rels/.rels``` if, and only if, a workbook with the default path xl/workbook.xml exists in the archive

## (aral-matrix) 29 September 2024 - Support for styles, merging cells (and more)
Merged development branch into the main branch. In summary:
* ```OpenXLSX/headers/XLStyles.hpp```: XLStyles class (and lots of subclasses) has been added, providing nearly complete access to all Excel formatting capabilities.
* ```OpenXLSX/headers/XLMergeCells.hpp``` and ```XLSheet.hpp```: XLMergeCells class is made accessible through XLWorksheet in order to create / delete cell merges
* ```Examples/Demo10.cpp``` demonstrates how styles and merges are used **Note:** The section that is disabled with ```testBasics = false``` *will* break the resulting Excel Spreadsheet if enabled, the only purpose is to demonstrate access to *all* new classes and methods. If you want to use them, make sure to use them correctly

*Note on XLNumberFormat(s)*: Contrary to all other XLStyles elements, these do not use an index within the XML as the referrable ID (XLCellFormat::setNumberFormatId), but instead a user-defined ID that can be set via XLNumberFormat::setNumberFormatId - and for an XLCellFormat, can be set to either a self-defined number format ID, or to a [format predefined by MS](https://learn.microsoft.com/en-us/dotnet/api/documentformat.openxml.spreadsheet.numberingformat?view=openxml-3.0.1). Generally, for custom formats, it is recommended to use IDs > 100.

### (aral-matrix) 29 September 2024 - prepare merge into main repository
* modified Demo9 to match style / behavior of other Demo programs
* re-created legacy ```XLDocument::create``` and ```XLDocument::saveAs``` function interfaces, but marked them as ```[[deprecated]]```. The new interfaces require explicit specification of ```XLForceOverwrite``` or ```XLDoNotOverwrite```. Once the deprecated function definitions can be removed, ```XLDoNotOverwrite``` could become the new default behavior
* moved nowide back into the correct location ```OpenXLSX/external/nowide/nowide```
* removed ```Demo0``` / kept it in the Makefile as a test vehicle
* updated ```Notes``` folder
* created ```Scripts``` folder with ```xml-format.sh``` (XML linting, useful to analyze XLSX zip contents in a text editor)
* moved ```make-gnu.sh``` to ```Scripts/make-gnu.sh```
* added ```Scripts/cmake-cleanup.sh``` to prepare (not execute!) commands that remove all temporary files generated by cmake
* added ```Scripts/demos-cleanup.sh``` to remove all xlsx files created by the Demos
* support for ```void setSavingDeclaration(XLXmlSavingDeclaration const& savingDeclaration)``` using ```class XLXmlSavingDeclaration``` (defined in ```XLXmlData.hpp```) that can be used to pass a custom XML version, encoding, and standalone property to pugixml

### (aral-matrix) September 2024 - to-do list:
- for more to-do items, refer to ```Notes/todo-list.txt```
- TBD: could XLRowData also benefit from passing through to setDefaultCellAttributes a column styles vector?
- completion of style support as much as is reasonable (not color themes, most likely) per known documentation of xl/styles.xml
- XLAlignmentStyle: check / throw if vertical alignments are used as horizontal and vice versa
- XLStyles ::create functions: implement good default style properties for all styles
- TBD: permit setting a format reference for shared strings

### (aral-matrix) 29 September 2024 (development-aral branch: 06 September) 2024 - enhance XLMergeCells and related XLWorksheet functionality

* ```XLWorksheet``` now allows to access an object managing the worksheet's merged cell ranges
  * ```XLMergeCells XLWorksheet::merges()``` - access the XLMergeCells class for the worksheet directly
  * ```void mergeCells(XLCellRange const& rangeToMerge, bool emptyHiddenCells = false)``` - merge cells defined by rangeToMerge
  * ```void mergeCells(const std::string& rangeReference, bool emptyHiddenCells = false)``` - merge cells defined by rangeReference
  * ```void unmergeCells(XLCellRange const& rangeToUnmerge)``` - unmerge cells defined by rangeToUnmerge
  * ```void unmergeCells(const std::string& rangeReference)``` - unmerge cells defined by rangeReference

* ```XLMergeCells```: added methods
  * ```int32_t XLMergeCells::findMerge(const std::string& reference)``` - find a merge matching reference
        * ```bool mergeExists(const std::string& reference)``` - test if a merge with reference exists
  * ```int32_t XLMergeCells::findMergeByCell(const std::string& cellRef)``` - find a merge containing std::string cellRef
  * ```int32_t XLMergeCells::findMergeByCell(XLCellReference cellRef)``` - find a merge containing XLCellReference cellRef
  * ```size_t count()``` - get count of merges defined in the worksheet
  * ```const char* merge(int32_t index)``` - get merge reference string at index
  * ```const char* operator[](int32_t index)``` - overload of operator[] as a shortcut to ::merge
  * ```int32_t appendMerge(const std::string& reference)``` - define a new merge, invoked by XLWorksheet::mergeCells
  * ```void deleteMerge(int32_t index)``` - delete merge with the given index from the worksheet (= unmerge cells), invoked by XLWorksheet::unmergeCells

* added example usage of this functionality to ```Demo10.cpp```

### (aral-matrix) 29 September 2024 (development-aral branch: 03 September 2024) - ignore worksheet internal subfolders that are not known (e.g. customXml)
* ```XLDocument::open``` will now ignore unknown subfolders (they remain unmodified and unaccessible in the zip in memory and stay in the archive upon saving). This prevents throwing an exception for any XLSX file written by a "creative" application that added items unknown to this library
* made a ```constexpr``` from ```const unsigned int pugi_parse_settings``` and moved it to ```XLDocument.hpp``` so that the const becomes available to XLStyles and XLSharedStrings
* XLStyles and XLSharedStrings now take care of creating a valid default document element, if an archive is missing the corresponding XML file or the document element is not present
* XLStyles constructor now ensures that cellFormats() has at least the default entry with index 0, so that a call to cellFormats().create() will not return this reserved index

### (aral-matrix) 29 September 2024 (development-aral branch: 02 September 2024) - major update with (nearly) complete styles support & cell merging
* implemented support for worksheet styles in ```XLStyles``` class - interface can be found in ```OpenXLSX/headers/XLStyles.hpp```
* support for merged cells
* ```Examples/Demo10.cpp``` demonstrates use of the new XLStyles & cell merging functionality
* plenty of bugfixes
* support for non-creating ```XLCellIterator```: can now iterate over a range and test ```XLCellIterator::cellExists``` before accessing it. This allows to skip non-existing cells without creating them.
* support for ```workbook##.xml```, XML namespaces and random 64bit (relationship) identifiers
  * a non-standard (== not ```xl/workbook.xml```) workbook XML name is now accepted if it is correctly referenced in ```_rels/.rels```
  * XLSX documents that use namespaces throughout their XML files are now supported in the following way:
          * ```bool OpenXLSX::enable_xml_namespaces()``` must be used to enable namespace support *before* opening a document using e.g. a namespace ```x``` (like so: ```<x:row r="1">```) everywhere
    * the document is then opened normally
    * any and all node creations will expose to the user normal node names (as if the namespaces were not in use) and will save/create elements with the correct namespace (of their parent node)
    * if a node is accessed with a namespace, the leading namespace will be stripped and then the node name will be checked based on the parent node's name
      * Example: ```insert_child_before("x:row", curRow )``` in the ```<y:sheetData>``` node will strip the ```x:``` and insert a row element named ```<y:row>```, using the parent node's namespace
    * all XMLNode functions where the namespace could be relevant (see ```OpenXLSX/headers/XLXmlParser.hpp```) take as an optional last argument a ```bool force_ns``` that - if true - will respect a namespace passed into the function for node creation / access. A helper ```const bool OpenXLSX::XLForceNamespace = true``` is available for code readability
      * Example: ```XMLNode::insert_child_before("x:row", curRow, XLForceNamespace)``` in the ```<y:sheetData>``` node like above, will insert a row element named ```x:row```
  * OpenXLSX by default assumes that worksheet relationship IDs are sequential and stored in the form ```id="rId##"``` where ```##``` is the sequence number, and when a new component is added to the workbook, a new relationship ID is determined by taking the highest existing value within the workbook, and adding +1 to it. During investigation of [https://github.com/troldal/OpenXLSX/issues/254] a workbook was found to use (seemingly) random 64 bit integers, stored in the form ```r:id="Rxx"```, with ```xx``` being a hexadecimal representation of a 64 bit integer.
    * ```OpenXLSX::UseRandomIDs()``` must be invoked to switch ID functionality *before* opening such a document
    * the document is then opened normally and new document components will be added with a 64 bit high quality randomizer, which should be reasonably safe to never cause a collision
    * (optional) ```OpenXLSX::UseSequentialIDs()``` can be used to restore default (sequential) relationship ID functionality

**NOTE** on ```enable_xml_namespaces```: Namespace support is transparent and can be used with documents that do not use such namespaces. However, it can have a small (<5%) performance impact on large workbooks and is therefore optional to enable.

**CAUTION** with ```UseRandomIDs```: Please be aware that a mixed mode, where one document is opened with random ID support and another without sequential relationship IDs, is not supported for the time being. If you have to work with documents of different types, you should always configure the desired relationship ID behavior for the next document, work with that, close it, and change the relationship ID configuration before opening the next document.

Please disregard Examples/Demo0.cpp and Examples/Demo9.cpp for now (Demo0 is trivial and was used to test non-standard workbook support, and Demo9 requires a review with better comments). Demo9 showcases how to use the new XLCellAssignable to copy-assign cell contents (like Excel copy & paste).

### (aral-matrix) 04 September 2024 - new features on the development branch:
* ```XLCellIterator``` no longer creates empty cells just for iterating over them, and provides ```::cellExists()``` to test if the currently pointed-to cell is already in the worksheet XML, before accessing it
* ```XLStyles``` support
* ```XLWorksheet``` now provides ```XLMergeCells``` support for merging / unmerging cell ranges
* ```Demo10.cpp``` has a lot of examples on how to use the new XLStyles functionality
* ignore ```customXml``` etc in the xlsx archive
* accept non-standard workbook names (if correctly identified in the relationships)
* support for documents with XML namespaces throughout the worksheets
* support for documents using non-sequential, random relationship IDs

### (aral-matrix) 02 September 2024 - ensure that all worksheets are contained in app.xml <TitlesOfParts> and reflected in <HeadingPairs> value for Worksheets

* Code refactored in ```XLProperties.cpp XLAppProperties``` to create ```<TitlesOfParts>``` and ```<HeadingPairs>``` nodes (and subnodes) if missing, added method ```alignWorksheets```, called by ```XLDocument::open``` to ensure that all worksheets listed in the workbook xml are also accounted for in ```docProps/app.xml```.
* Started to encapsulate whitespace "pretty format" support in a separate function to remove clutter from the functional code -> ```XLProperties.cpp prettyInsertXmlNodeBefore```, maybe this can eventually become a global function, paired with a TBW function ```prettyInsertXmlNodeAfter```, and could be used by all classes, cleaning up the code for whitespace support substantially.
* changed some confusing variable names in ```XLProperties.cpp``` for ```<HeadingPairs>``` subnodes: ```pairCount``` -> ```pairValueParent```, ```pairCountValue``` -> ```pairValue```

### (aral-matrix) 01 September 2024 - ignore phonetic tags consistently in shared strings table

Code refactored in XLDocument::open to read the shared strings table while consistently ignoring phonetic tags, which were previously only ignored if the very first child of an ```<si>``` tag was a phonetic tag. Will now be ignored anywhere before, after or in between text ```<t>``` and rich text ```<r>``` tags.

### (aral-matrix) 31 August 2024 - added fallback solution to get document relationships

Included a "dumb" fallback solution in ```XLRelationships.cpp GetTypeFromString``` to support previously unknown relationship domains, e.g. ```type="http://purl.oclc.org/ooxml/officeDocument/relationships/worksheet"```. Altered behavior will initially test against the hardcoded relationship domains, and if that test fails to identify a relationship type string, the type string will be searched for an occurrence of ```/relationships/``` and if that substring is found, the type detection fallback will try to evaluate the relationship type based on the substring starting with ```/relationships/```, ignoring the domain. For the above example, that would result in a test of ```typeString.substr( comparePos ) == "/relationships/worksheet"```, where comparePos == 41 (the position at which substring ```/relationships/``` begins).

In anticipation of a potential future need for a similar "dumb" fallback solution, repeating hardcoded strings in ```XLContentTypes.cpp GetTypeFromString``` were also replaced with string constants.

Updated .gitignore to a more generic version that excludes everything and explicitly re-includes all desired files.

### (aral-matrix) 19/20 August 2024 updated pull requests
Closed a multitude of pull requests that had been implemented in the May 2024 Update, implemented two more editorials from PR #246 and #253.

### (aral-matrix) 18 August 2024 - minor bugfixes and elimination of warnings
* BUGFIX XLRelationships.cpp `BinaryAsHexString`: replaced char array with std::string, as ISO C++ standard does not permit variable size arrays
* BUGFIX XLRelationships.cpp `Rand64`: added explicit type cast, as bitwise shift-left does *not* do integer promotion to long on the left operand
* Makefile.GNU: added warning flags `-Wpedantic -Wextra` and **removed all previously disabled flags after below patches**
* reformatted whitespaces in XLRelationships.cpp to align with project style (`f( param )` -> `f(param)`, `a[ index ]` -> `a[index]` and `if( condition )` -> `if (condition)`)
* Eliminate some warnings:
  * zippy.hpp: assign explicit uint64_t type to a nameless enum to address `warning: enumerated and non-enumerated type in conditional expression [-Wextra]`
  * zippy.hpp: added typecasts to void on function parameters for functions that are not yet implemented, also added explicit exceptions to ensure those functions are never invoked
    * affects:
      * `void ZipArchive::Save(std::ostream& stream)`
      * `void ZipArchive::ExtractDir(const std::string& dir, const std::string& dest)`
      * `void ZipArchive::ExtractAll(const std::string& dest)`
  * XLDocument.cpp: disabled `-Wunused-function` by pragma for functions `fileExists` and `isDirectory`
  * XLRow.hpp & .cpp: changed return type of rowNumber to `uint32_t` (was `uint64_t`). **CAUTION**: there is no validity check on the underlying XML (nor was there ever one in case a value was inconsistent with OpenXLSX::MAX_ROWS)
  * changed some loop variable types, modified range checks and added static_cast instructions to eliminate `-Wsign-compare`
    * affects: XLCellReference.cpp, XLMergeCells.cpp, XLSharedStrings.cpp, Demo9.cpp
  * XLCellIterator.hpp: removed const-ness of return value of `bool endReached()` to eliminate `-Wignored-qualifiers` (ignored because const on trivial return types accomplishes nothing)
  * added utilities/XLUtilities.cpp `OpenXLSX::ignore` template, can be used to suppress `-Wunused-parameter` and `-Wunused-variable` like so: `OpenXLSX::ignore(unusedValue)`
    * now used in: XLComments.cpp, XLStyles.cpp
  * XLXmlParser.cpp XMLNode::namespaced_name_shared_ptr: made no-op lambda parameter unnamed to eliminate `-Wunused-parameter`
  * Demo10.cpp: cast command line parameters to void to suppress -Wunused-parameter
  * wrapped all `#pragma warning` lines in another pragma to disable `-Wunknown-pragmas` (on gcc/g++)
    * wrapper pragma:
      * `#pragma GCC diagnostic push`
      * `#pragma GCC diagnostic ignored "-Wunknown-pragmas" // disable warning about below #pragma warning being unknown`
      * `#   pragma /* offending lines go here */`
      * `#pragma GCC diagnostic pop`
    * affects: 
      * `zippy.hpp`
      * `IZipArchive.hpp`
      * `XLCell.hpp`
      * `XLCellIterator.hpp`
      * `XLCellRange.hpp`
      * `XLCellReference.hpp`
      * `XLCellValue.hpp`
      * `XLColor.hpp`
      * `XLColumn.hpp`
      * `XLCommandQuery.hpp`
      * `XLContentTypes.hpp`
      * `XLDateTime.hpp`
      * `XLDocument.hpp`
      * `XLException.hpp`
      * `XLFormula.hpp`
      * `XLMergeCells.hpp`
      * `XLProperties.hpp`
      * `XLRelationships.hpp`
      * `XLRowData.hpp`
      * `XLRow.hpp`
      * `XLSharedStrings.hpp`
      * `XLSheet.hpp`
      * `XLStyles.hpp`
      * `XLWorkbook.hpp`
      * `XLXmlData.hpp`
      * `XLXmlFile.hpp`
      * `XLZipArchive.hpp`
      * `Examples/Demo5.cpp`

### (aral-matrix) 17 August 2024 - bugfix in XLAppProperties::createFromTemplate
* BUGFIX: TitlesOfParts is now correctly inserted into the `<Properties>` (document) element, was previously wrongly appended to headingPairs
* entries in /xl/ are now explitly checked for known & handled file types (`/xl/worksheets/sheet*`, `/xl/sharedStrings.xml`, `/xl/styles.xml`, `/xl/theme/theme*`) and otherwise ignored. This fixes an issue when the workbook contains `/xl/pivotCache/` and `/xl/pivotTables/` entries until support for those is implemented (if ever ;P)

### (aral-matrix) 14 August 2024 - use row style, or if not set, column style for default cell style
* Newly created cells will now use the style that is set for the row or the column (if set and != XLDefaultCellFormat), with row style taking precedence
  * added XLUtilities.hpp getColumnStyle which retrieves the column style for a given column index from the `<cols>` element obtained via a rowNode parent's parent
  * added XLUtilities.hpp setDefaultCellAttributes, which sets the cell reference and the cell style, taking an optional vector of column styles that will improve performance using a previously extracted set of column styles
  * XLRowData now uses setDefaultCellAttributes after creating a new cell
  * XLUtilities.hpp getCellNode now takes the same optional vector of column styles and passes it on to setDefaultCellAttributes, which is now used after creating a new cell
  * XLCellIterator constructor now requires a pointer to a column styles vector (size can be 0) which is used when new cells need to be created
  * XLCellRange now has a new member `std::vector< XLStyleIndex > m_columnStyles`, and a method fetchColumnStyles that will populate the vector so that it can be passed to the XLCellIterator constructor
    * if used, the optimization function has to be called *after* all column styles for the range are configured - columns configured afterwards will result in cells not getting the format setting
    * if the function is not used, each cell creation will result in a call to getColumnStyle, which has a small performance impact (<5%) for few columns, but is likely to be more impactful with the amount of formatted columns increasing
* the remaining XLSheet cell() functions (taking an XLCellReference or a rowNumber / columnNumber) have been modified to return an XLCellAssignable
  * unchanged: XLCellAssignable XLWorksheet::cell(const std::string& ref) const
  * return type changed: XLCellAssignable cell(const XLCellReference& ref) const
  * return type changed: XLCellAssignable cell(uint32_t rowNumber, uint16_t columnNumber) const;
  * the XLCellAssignable is now constructed in the latter method, and the other two pass through the return value of this latter method
  
### (aral-matrix) 11 August 2024 - support for non-creating XLCellIterators, iterator performance patch, bugfix
* XLCellIterators can now be used to iterate over a range and *test* `XLCellIterator::cellExists()` without creating the XML for the cell.
* cell (and row) XML will now only be created when an XLCellIterator is dereferenced
* Performance improvement: Execution time on Demo5 is down from (on my test system) 86 seconds to 75 seconds (-12.8%)
* XLCellIterator bugfix since last commit: m_hintCell (now m_hintNode) was being initialized to other.m_currentCell (should have been other.m_hintCell) in copy constructor and copy assignment operator

### (aral-matrix) 08 August 2024 - support for XLWorksheet::mergeCells and ::unmergeCells
* support for XLWorksheet::mergeCells and unmergeCells (with XLCellRange or std::string range reference parameter, option to clear cell contents)
  * added XLWorksheet new method ::mergeCells with parameter emptyHiddenCells (and convenience const bool XLEmptyHiddenCells = true)
  * added XLWorksheet new method ::unmergeCells
  * added XLCell::clear method with bitwise-OR combineable flags: XLKeepCellStyle, XLKeepCellType, XLKeepCellValue, XLKeepCellFormula 
  * added new module XLMergeCells.hpp / XLMergeCells.cpp
* XLCellRange constructor: added XLInputError exception when range is constructed with a topLeft cell that is to the right or lower than bottomRight cell
* Demo10: included a demonstration of mergeCells

### (aral-matrix) 01 August 2024 - xl/styles.xml - support for XLFill patternFill all pattern types, XLFonts scheme & vertAlign, all XLAlignmentStyle values
* patternFill now supports all patternType values per standard
* XLFonts now support scheme major/minor/none (`<font><scheme val="major"/></font>`)
* XLFonts now support vertical align run style (`<font><vertAlign val="subscript"/></font>`)
* XLAlignmentStyle can now be used with all defined horizontal and vertical alignment styles
* Examples/Demo10.cpp has been updated to test some(!) of the new formatting elements

### (aral-matrix) 31 July 2024 - xl/styles.xml - support for fill::gradientFill and XLDataBarColor
* gradientFill elements within `<fills><fill><gradientFill>...</gradientFill></fill>...</fills>` are now supported
* along with that come a few new classes: XLGradientStops, XLGradientStop, XLDataBarColor
* XLLine color properties are now controlled via the XLDataBarColor as well

### (aral-matrix) 29 July 2024 - support for workbook##.xml and XML namespaces
* it appears that a workbook does not always have to be at xl/workbook.xml
  * --> the workbook path is now read from the document relationships, if it has an entry for "officeDocument"
* also, XML namespaces can be used for node names throughout (almost) all XML files as long as they are defined in the document root(?) node with xmlns:<namespace> - e.g. xmlns:x
  * added functions enable_xml_namespaces and disable_xml_namespaces
  * when enable_xml_namespaces() was invoked, XLXmlParser XMLNode now wraps all pugi::xml_node methods so that a node referred to by a name will be found regardless of namespace, and children will be created automatically inheriting the node's own namespace

### (aral-matrix) 21 July 2024 - xl/styles.xml - support for cell formatting in work
Please refer to Demo10 and XLStyles.hpp on how to set cell formatting.
In short:
* size_t XLCell::cellFormat() and bool XLCell::setCellFormat(size_t cellFormatIndex)
* these functions get/set an index to a format defined in xl/styles.xml <styleSheet>:<cellXfs>
* <cellXfs> refers to 
  * numFmtId -> XLStyles::numberFormats().numberFormatById( uint32_t numberFormatId ) // where numberFormatId is the numFmtId attribute of the numFmt entry
  * fontId -> XLStyles::fonts().fontByIndex( fontId )
  * fillId -> XLStyles::fills().fillByIndex( fillId )
  * borderId -> XLStyles::borders().borderByIndex( borderId )
  * xfId -> XLStyles::cellStyleFormats( xfId ) // xfId appears to refer to entries in the <cellStyleXfs> array - untested currently
* it is not yet clear what the purpose of the <cellStyles> array is
* all array getter functions (numberFormats, fonts, fills, borders, cellStyleFormats, cellFormats, cellStyles) support the operator[] to access an object by index
* all objects provide getter and setter functions for all supported attributes. Especially in the color domain, there's probably quite a bit of support missing at this stage
* color support: only rgb via XLColor (XLColor::hex()) is supported at this stage. In particular, no color themes are supported

## Credits

- Thanks to [@zeux](https://github.com/zeux) for providing the awesome
  PugiXML library.
- Thanks to [@richgel999](https://github.com/richgel999) for providing
  the miniz library.
- Thanks to [@tectu](https://github.com/Tectu) for cleaning up my
  CMakeLists.txt files.

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