std::experi...stem::exists(3)

💖 NAME 💖

okay bestie, welcome to std::experi...stem::exists(3) — yes, the title is literally truncated like that — from the C++ Standard Libary manual (spelling exactly as it appears here, no cap). The thing being documented is std::experimental::filesystem::exists, and the NAME line is the same name twice: std::experimental::filesystem::exists - std::experimental::filesystem::exists. iconic. 💅

✨ Synopsis ✨

Defined in header <experimental/filesystem> 🫶

bool exists( file_status s )                 (1) (filesystem TS)
bool exists( const path& p );                (2) (filesystem TS)
bool exists( const path& p, error_code& ec )

This function checks if the given file status or path corresponds to an existing file or directory. Here's the breakdown:

1. Equivalent to status_known(s) && s.type() != file_type::not_found.
2. Equivalent to exists(status(p)) or exists(status(p, ec)) (symlinks are followed). The non-throwing overload returns false if an error occurs.

🌸 Parameters 🌸

• s — file status to check
• p — path to examine
• ec — out-parameter for error reporting in the non-throwing overload

🦋 Return value 🦋

true if the given path or file status corresponds to an existing file or directory, false otherwise. periodt. ✨

🔥 Exceptions 🔥

1. noexcept specification: noexcept.
2. The overload that does not take an error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking an error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. This overload has noexcept specification: noexcept.

💡 Notes 💡

The information provided by this function is usually also provided as a byproduct of directory iteration. During directory iteration, calling exists(*iterator) is less efficient than exists(iterator->status()). iykyk 👑

🎀 Example 🎀

The original page says // Run this code before the snippet, so here it is in all its glory:

#include <cstdint>
#include <experimental/filesystem>
#include <fstream>
#include <iostream>
namespace fs = std::experimental::filesystem;

void demo_exists(const fs::path& p, fs::file_status s = fs::file_status{})
{
    std::cout << p;
    if (fs::status_known(s) ? fs::exists(s) : fs::exists(p))
        std::cout << " exists\n";
    else
        std::cout << " does not exist\n";
}

int main()
{
    fs::create_directory("sandbox");
    std::ofstream("sandbox/file"); // create regular file
    fs::create_symlink("non-existing", "sandbox/symlink");

    demo_exists("sandbox");
    for (auto it = fs::directory_iterator("sandbox"); it != fs::directory_iterator(); ++it)
        demo_exists(*it, it->status()); // use cached status from directory entry
    fs::remove_all("sandbox");
}

Output:

"sandbox" exists
"sandbox/file" exists
"sandbox/symlink" does not exist

🌈 See also 🌈

• status — determines file attributes
• symlink_status — determines file attributes, checking the symlink target (function)
• file_status — represents file type and permissions (class)
• status — cached status of the file designated by this directory entry
• symlink_status — cached symlink_status of the file designated by this directory entry (public member function of std::experimental::filesystem::directory_entry)

👑 Categories 👑

• Noindexed pages
• unconditionally noexcept

🙈 Hidden categories 🙈

• Pages with unreviewed unconditional noexcept template
• Pages with unreviewed noexcept template

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mwah 💋 — this iconic page came from http://cppreference.com, version/date 2024.06.10, and it's literally std::experi...stem::exists(3). slay. 🫶