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Build failure on GCC/MinGW (MXE): std::ifstream constructor mismatch with Platform::filenameToUTF()

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
cpp
Domain
build-system

Research direction

Start in src/OpenColorIO/transforms/FileTransform.cpp and inspect the std::ifstream construction using Platform::filenameToUTF(filepath). Build OpenColorIO with GCC/MinGW-w64 or MXE to reproduce the std::wstring overload failure, then verify that the path handling compiles and works across the affected configurations.

Written by the indexing model from the issue text.

Description

Description

OpenColorIO 2.5.1 fails to compile under GCC / MinGW-w64 (including MXE cross builds) due to inconsistent file path type handling in Platform::filenameToUTF() when used with std::ifstream in FileTransform.cpp.

The failure occurs when constructing a std::ifstream from the result of Platform::filenameToUTF(filepath), where the returned type may vary between std::string and std::wstring depending on build configuration (_WIN32 && UNICODE).

This leads to template overload resolution failures under GCC/libstdc++ when a std::wstring is involved in std::ifstream construction.

Error observed (GCC / libstdc++)

error: no matching function for call to
std::basic_ifstream<char>::basic_ifstream(const std::wstring, std::ios_base::openmode)

Affected code src/OpenColorIO/transforms/FileTransform.cpp:

std::ifstream(Platform::filenameToUTF(filepath), mode)

Root cause

  • Platform::filenameToUTF() is conditionally typed:
  • std::wstring on _WIN32 && UNICODE
  • std::string otherwise
  • std::ifstream construction from std::wstring is not consistently supported across standard library implementations
  • GCC/libstdc++ rejects this usage, while MSVC may accept it depending on STL implementation details
  • This creates a portability issue in file I/O path handling

Impact

  • Breaks MXE / MinGW-w64 cross compilation
  • Causes divergence between MSVC and GCC builds
  • Introduces non-portable file path handling in core I/O utilities

Suggested fix

Avoid passing platform-dependent string types directly into std::ifstream construction.

This is the C++17-compatible solution that worked:

auto path = Platform::filenameToUTF(filepath);
return std::make_unique<std::ifstream>(path.c_str(), mode);
Dominant language
C++
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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  4. Open a pull request that references the issue number.

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