std::filesy..._error::what(3)

✨ std::filesystem::filesystem_error::what ✨

okay bestie, so this is like, the manual page for std::filesystem::filesystem_error::what, which lives in the C++ Standard Libary (yes that's a typo in the original, we're keeping it, it's iconic). it's giving "exception tea" and honestly? we're obsessed. let me spill 💅

🌸 Synopsis 🌸

const char* what() const noexcept override;  (since C++17)

so like, since C++17, this lil function is const, it's noexcept, and it overrides. periodt.

💖 Description 💖

okay so what() returns an explanatory byte string. and like, this explanatory string contains the explanatory string that was passed at the time of construction. i know, very "the what contains the what," very main character energy. 🎀

implementations are encouraged to include the pathnames of path1() and path2() in native format, and also the std::system_error::what() string inside the returned string as well. so like, the vibes are "here's what went down, here's the paths, and here's the system error lore." no cap. ✨

🦋 Parameters 🦋

• (none) — literally nothing, empty, the void, a blank canvas, she takes no arguments, she's low maintenance like that 💅

👑 Return value 👑

a C-style explanatory byte string (the original says "C-stye" and we're keeping that too, it's a moment) that contains the explanatory string passed at the time of construction. so like, what you put in is what you get out. fr fr. 🌸

🔥 Example 🔥

run this code bestie, it's a whole vibe

#include <cstdio>
#include <filesystem>
#include <iostream>
#include <string_view>
namespace fs = std::filesystem;

void explain(std::string_view note, fs::filesystem_error const& ex)
{
    std::cout << note << " exception:\n"
              << "what(): " << ex.what() << '\n'
              << "path1(): " << ex.path1() << ", path2(): "
              << ex.path2() << "\n\n";
}

int main()
{
    try
    {
        std::filesystem::rename("/dev", "/null");
    }
    catch(fs::filesystem_error const& ex)
    {
        explain("fs::rename()", ex);
    }

    for (auto const path : {"/bool", "/bin/cat", "/bin/mouse"})
        try
        {
            std::filesystem::create_directory(path);
        }
        catch(fs::filesystem_error const& ex)
        {
            explain("fs::create_directory()", ex);
        }
}

🌈 Possible output 🌈

like, this is what it might look like when you run it, depending on your system and your whole situation:

fs::rename() exception:
what(): filesystem error: cannot rename: Permission denied [/dev]
[/null]
path1(): "/dev", path2(): "/null"

fs::create_directory() exception:
what(): filesystem error: cannot create directory: Permission denied
[/bool]
path1(): "/bool", path2(): ""

fs::create_directory() exception:
what(): filesystem error: cannot create directory: File exists
[/bin/cat]
path1(): "/bin/cat", path2(): ""

fs::create_directory() exception:
what(): filesystem error: cannot create directory: Read-only file
system [/bin/mouse]
path1(): "/bin/mouse", path2(): ""

like, the what() string is doing the absolute most, slaying the explanation, and then path1() and path2() are there too, giving coordinates. iconic. 🫶

ngl bestie, this function is literally just "tell me what went wrong" but make it C++ and make it noexcept. very demure, very mindful.

okay that's the whole page! this was from http://cppreference.com, dated 2024.06.10, and the manual is std::filesy..._error::what(3) — yes the title got truncated, it's giving "the way that the manpage tool can't fit filesystem_error in the header," we still love her. bye bestie, go catch those filesystem errors 💜✨