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From: "thiago at kde dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/111244] New: std::filesystem::path encoding mismatches
 locale on Windows
Date: Wed, 30 Aug 2023 19:10:19 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.2.1
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: thiago at kde dot org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111244

            Bug ID: 111244
           Summary: std::filesystem::path encoding mismatches locale on
                    Windows
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thiago at kde dot org
  Target Milestone: ---

Test:
$ cat fstest.cpp=20
#include <filesystem>
#include <stdio.h>

int main(int argc, char **argv)
{
    for (int i =3D 1; i < argc; ++i) {
        std::filesystem::path p(argv[i]);
        if (std::filesystem::exists(p)) {
            printf("%s %llu\n", argv[1], (unsigned long
long)std::filesystem::file_size(p));
        } else {
            printf("%s does not exist\n", argv[1]);
        }
    }
}
$ touch fil=C3=A6
$ g++ fstest.cpp
$ ./a.out fstest.cpp fil=C3=A6

On Linux (and any other Unix):
fstest.cpp 377
fstest.cpp 0

On Windows with libc++ or MS STL:
fstest.cpp 377
fstest.cpp 0

On Windows with libstdc++:
fstest.cpp 377
terminate called after throwing an instance of
'std::filesystem::__cxx11::filesystem_error'
  what():  filesystem error: Cannot convert character sequence: Illegal byte
sequence

This is caused by std::filesystem::path interpreting the input as UTF-8. On
Windows, it's not; it must be decoded using the locale codec.=20

Strictly speaking, the same should apply to the conversion to Unicode on Un=
ix
systems too, but a) they're almost all UTF-8 these days, so the corner cases
may be ignored by a policy decision and b) the mismatch of input does not l=
ead
to inability to refer to files by fs::path alone.=