failed to print error code `:s` fail on windows due to encoding error

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@shreyas-s1403 is already working on this.

Since Oct 23, 2026.

  • #4774 by @wyf027 — closed without merging
  • #4883 by @ameliabarnabyhub — closed without merging
  • #4884 by @hannahgreendesk — closed without merging

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp
Domain
tooling

Research direction

Start by compiling and running the supplied filesystem-error reproducer on Windows, then trace how fmt handles std::error_code with the {:s} formatter. Done means the example prints the error code without an encoding exception while preserving the other displayed values.

Written by the indexing model from the issue text.

Description

#include <exception>
#include <filesystem>
#include <iostream>

#include "fmt/ostream.h"
#include "fmt/std.h"

namespace fs = std::filesystem;

int main() {
    const fs::path from{"/none1/a"}, to{"/none2/b"};

    try {
        fs::copy_file(from, to);
    } catch (fs::filesystem_error const &ex) {
        std::cout << "what():  " << ex.what() << '\n'
                  << "path1(): " << ex.path1() << '\n'
                  << "path2(): " << ex.path2() << '\n'
                  << "code().value():    " << ex.code().value() << '\n'
                  << "code().message():  " << ex.code().message() << '\n'
                  << "code().category(): " << ex.code().category().name() << '\n';

        try {
            fmt::println("{:s}", ex.code());
        } catch (std::exception &e) {
            fmt::println("fmt error: {}", e.what());
        }
    }

    fmt::println("exit");
    return 0;
}
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  4. Open a pull request that references the issue number.

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