MSVC .dll build FAILED without indication as to why (fails only for vcpkg port)

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31-08-2024

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MSVC .dll Build Failures: A Vcpkg Mystery

This article explores a common problem encountered when building projects using MSVC and Vcpkg. The issue involves a C++ library that builds successfully in Visual Studio but fails to build as a shared library (.dll) when using Vcpkg, specifically when using a custom overlay port.

We'll delve into the problem's manifestation, examine possible causes, and discuss solutions drawn from Stack Overflow insights. While the specific source code is not provided, the article aims to offer a general understanding of the problem and how to approach debugging it.

The Problem: A Silent Build Failure

The user's library builds flawlessly in Visual Studio 2022 and with WSL/g++, but fails during the Release configuration build when using Vcpkg. The build process halts without any specific error message, simply indicating "BUILD_FAILED." The install-x64-windows-rel-out.log file shows a successful build process until the very end where the link command mysteriously fails.

Possible Causes:

Several factors can contribute to a silent build failure like this. Here's a breakdown with explanations and insights from Stack Overflow:

1. Vcpkg Dependency Issues:

   • Issue: Vcpkg manages dependencies for your project. Incorrect dependencies or conflicts could lead to unexpected errors during the linking stage.
   • Solution: Carefully examine the dependencies listed in your portfile.cmake and the Vcpkg registry to ensure they are compatible with your build configuration and compiler.
   • Stack Overflow Insights:
     • "Vcpkg build error: no target found with name '...' (user suggests checking the target name and making sure it is correct)
     • "How to debug a Vcpkg build error?" (user advises enabling verbose logging during build and checking for warnings)

2. Compiler/Linker Configuration Discrepancies:

   • Issue: The build settings within Visual Studio might not be replicated accurately in the Vcpkg build environment. This can lead to inconsistencies in compilation flags, include paths, or linker settings.
   • Solution: Check the portfile.cmake file for specific flags or settings being passed to the compiler and linker. Ensure these match the settings used in your Visual Studio project. Additionally, examine the install-x64-windows-rel-out.log file for any warnings or errors related to missing header files or library paths.
   • Stack Overflow Insights:
     • "Building a shared library with vcpkg causes undefined symbols in another library" (user explains the importance of ensuring dependencies are built as static libraries if your project relies on them)
     • "Vcpkg - How to link to a static library" (user explains the process of building and linking static libraries within Vcpkg)

3. DLL Export Issues:

   • Issue: Exporting functions from a DLL incorrectly can lead to linker errors.
   • Solution: Ensure that the functions you intend to export from your DLL are correctly declared using the __declspec(dllexport) keyword. Make sure your export list is accurately defined in an .def file, if used.
   • Stack Overflow Insights:
     • "Undefined reference to ... when linking static library to shared library" (user addresses undefined reference issues when linking static and shared libraries)
     • "Vcpkg: Undefined symbols when linking static library to shared library" (user highlights the importance of correct dependency linkage between static and shared libraries)

4. Precompiled Headers (PCH):

   • Issue: Precompiled headers can cause issues if used differently between Visual Studio and Vcpkg.
   • Solution: Check if you're using PCH in your Visual Studio project. If so, ensure the same approach is being used in the portfile.cmake file. Consider disabling PCH during the Vcpkg build process.
   • Stack Overflow Insights:
     • "Precompiled headers not working when using vcpkg" (user explains how to use precompiled headers correctly with Vcpkg)

The Solution: Static Library Workaround

The user found that by forcing their library to build as a static library using vcpkg_check_linkage(ONLY_STATIC_LIBRARY), the issue was resolved. This suggests that the problem likely lies in the way the shared library is built by Vcpkg.

Conclusion

This case highlights the importance of carefully managing dependencies, build settings, and library linkage when using Vcpkg. Understanding how Vcpkg operates and ensuring consistency with your Visual Studio project settings are crucial steps in preventing silent build failures. The solution provided by the user underscores the potential for static libraries to overcome complex DLL linking issues. Always remember to consult the Vcpkg documentation and Stack Overflow for comprehensive solutions and troubleshooting guidance.