https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95749
Bug ID: 95749 Summary: std::filesystem::file_size returns wrong size for large files on Windows Product: gcc Version: 10.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: reiter.christoph at gmail dot com Target Milestone: --- Downstream report: https://github.com/msys2/MINGW-packages/issues/6585 ---- #include <filesystem> #include <fstream> #include <iostream> #include <stdint.h> #include <stdio.h> int main(int argc, char** argv) { uint64_t std_filesystem_file_size; uint64_t std_fstream_file_size; std::filesystem::path sourceFile = std::filesystem::current_path() / "example_3GiB.bin"; std::ofstream ofs(sourceFile); ofs << "this is some text in the new file\n"; ofs.close(); std::filesystem::resize_file(sourceFile,3221225472); std_filesystem_file_size = std::filesystem::file_size(sourceFile); std::ifstream in(sourceFile.string(), std::ifstream::ate | std::ifstream::binary); std_fstream_file_size = in.tellg(); std::cout << "3 GiB file:" << std::endl; std::cout << "std_filesystem_file_size: " << std_filesystem_file_size << std::endl; std::cout << "std_fstream_file_size: " << std_fstream_file_size << std::endl; return 0; } ---- $ g++ -std=c++17 a.cpp $ ./a.exe 3 GiB file: std_filesystem_file_size: 18446744072635809792 std_fstream_file_size: 3221225472 ---- The first value is wrong. My uneducated guess would be that https://github.com/gcc-mirror/gcc/blob/41d6b10e96a1de98e90a7c0378437c3255814b16/libstdc%2B%2B-v3/src/filesystem/ops-common.h#L66 should use _wstat64() instead of _wstat and stat_type should be _stat64 instead of _stat, otherwise things are limited to 32bit. See https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/stat-functions?view=vs-2019 for details.