How to open an std::fstream (ofstream or ifstream) with a unicode filename?

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The C++ standard library is not Unicode-aware. char and wchar_t are not required to be Unicode encodings.

On Windows, wchar_t is UTF-16, but there’s no direct support for UTF-8 filenames in the standard library (the char datatype is not Unicode on Windows)

With MSVC (and thus the Microsoft STL), a constructor for filestreams is provided which takes a const wchar_t* filename, allowing you to create the stream as:

wchar_t const name[] = L"filename.txt";
std::fstream file(name);

However, this overload is not specified by the C++11 standard (it only guarantees the presence of the char based version). It is also not present on alternative STL implementations like GCC’s libstdc++ for MinGW(-w64), as of version g++ 4.8.x.

Note that just like char on Windows is not UTF8, on other OS’es wchar_t may not be UTF16. So overall, this isn’t likely to be portable. Opening a stream given a wchar_t filename isn’t defined according to the standard, and specifying the filename in chars may be difficult because the encoding used by char varies between OS’es.

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