Update MSVC compiler options and CMake configuration for 1.5.1

[j2doll]

This pull request updates the QXlsx library to improve C++ standard handling, enhance MSVC compatibility, and clean up some legacy code and configuration. The most important changes are grouped below:

Build System and C++ Standard Improvements:

• Updated the QXlsx library version from 1.5.0 to 1.5.1 in CMakeLists.txt to reflect the new release.
• Enhanced C++ standard selection in QXlsx.pri: now sets C++11 for Qt 5 and C++17 for Qt 6, with messages for clarity.

MSVC and Cross-Platform Compatibility:

• Added a workaround in xlsxglobal.h for MSVC to define make_checked_array_iterator and ensure compatibility with MSVC's standard library extensions.
• For MSVC builds, forced the /permissive compile flag in CMakeLists.txt to override /permissive- and avoid standards compliance issues.

Code and Configuration Cleanup:

• Removed a hard-coded QXlsx version string from mainwindow.cpp as it is now managed in the build system.
• Cleaned up the project file by removing unused header and source entries related to xlsxreadsax from QXlsx.pro.

[sonarqubecloud]

Quality Gate failed

Failed conditions
B Maintainability Rating on New Code (required ≥ A)

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[dantti]

@j2doll what do you think about dropping qmake and Qt5 support? It's pretty much EOL

[j2doll]

@j2doll what do you think about dropping qmake and Qt5 support? It's pretty much EOL

Thank you for reporting.

I agree with that. Qt5 seems to have ended. 💀

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Qt 5.15 LTS Support Lifetime Summary

📅 Support End Dates by License

• Open Source (Community): December 8, 2020
  (Public patch releases were restricted 6 months after the initial launch).
• Standard Commercial: May 26, 2023
  (Standard 3-year commercial support window).
• Commercial Extended Support: May 26, 2025
  (An additional 2-year extension, marking the absolute end of the standard LTS lifecycle).

⚠️ Current Status (As of 2026)

• End of Life (EoL): All standard and extended support for Qt 5.15 LTS has officially expired. No further regular bug fixes or security patches are being released.
• Migration Recommended: It is highly recommended to migrate legacy systems to Qt 6 LTS (such as Qt 6.5 LTS or Qt 6.8 LTS) to ensure ongoing security, platform compatibility, and technical support.

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If we use Qt 6, There are things to consider.
We need to upload the C++ version with Qt 6.
Currently, QXlsx only uses modern c++ at the C++11 level.

If any one have any opinions on this, please leave a comment. 📫

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Qt 6 and C++ version

Qt 6 requires C++17 as the minimum baseline for both building the framework itself and developing applications with it.

While the minimum requirement remains C++17 across all minor versions (from Qt 6.0 up to Qt 6.8+), newer minor versions continuously expand support for newer C++ standards ($C++20$ and $C++23$) and introduce stricter requirements for specific modules.

C++ Requirements by Qt 6 Minor Version

Qt Version	Minimum C++ Standard	Key Changes & Standard Support
Qt 6.0 ~ 6.2 LTS	C++17	C++17 became the strict baseline for Qt 6. Started adding partial support for C++20 features (e.g., designated initializers).
Qt 6.3 ~ 6.5 LTS	C++17	Enhanced integration with std::chrono and expanded C++20-related macros and helper functions.
Qt 6.6 ~ 6.7	C++17	Improved compatibility with C++20 containers. Active compiler testing for C++23 compatibility.
Qt 6.8 LTS ~ 6.9+	C++17

(C++20 for certain modules) | Qt WebEngine and other Chromium-based modules now strictly require a C++20 compiler. Deeper integration with C++20/C++23 standard library features. |

Key Highlights & Considerations

• Framework Baseline: You must use a compiler that supports at least C++17 to build or develop with any Qt 6 version (upgraded from the C++11 baseline in Qt 5).
• The Qt WebEngine Exception: Starting from Qt 6.8 LTS, the Qt WebEngine module requires a C++20 compiler due to upstream Chromium updates. If your project utilizes WebEngine, your build environment must be set to C++20.
• Using C++20/C++23 in Your Code: Even though Qt 6 is built on C++17, you can freely set CMAKE_CXX_STANDARD to 20 or 23 in your own project's CMakeLists.txt. Qt 6 fully supports this, and newer minor versions (especially Qt 6.5+) offer much smoother type conversions between Qt types and modern C++ types (like QDateTime and std::chrono).

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