std::filesy...try::assign(3)

hii bestie 💖 this is the std::filesy...try::assign(3) page from the C++ Standard Libary manual, and we’re about to make directory_entry::assign make sense. no cap. ✨

💖 NAME 💖

std::filesystem::directory_entry::assign — std::filesystem::directory_entry::assign

(the manpage really says it twice, and honestly? iconic. 💅)

🌸 Synopsis 🌸

okay so there are two overloads, both since C++17, and here they are exactly:

• (1) (since C++17) — void assign( const std::filesystem::path& p );
• (2) (since C++17) — void assign( const std::filesystem::path& p, std::error_code& ec );

Assigns new content to the directory entry object. Sets the path to p and calls refresh to update the cached attributes. If an error occurs, the values of the cached attributes are unspecified. 🫶

important vibe check: This function does not commit any changes to the filesystem. it’s giving “look, don’t touch” energy, periodt. 💅

🎀 Parameters 🎀

• p — path to the filesystem object to which the directory entry will refer. 🛤️
• ec — out-parameter for error reporting in the non-throwing overload. 🩹

🦋 Return value 🦋

(none) — literally nothing comes back, bestie. 🫶

💅 Exceptions 💅

Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails. 😭 memory said no.

1. Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument. 🔥
2. Sets a std::error_code& parameter to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. ✅

🌈 Example 🌈

// Run this code

#include <filesystem>
#include <fstream>
#include <iostream>

void print_entry_info(const std::filesystem::directory_entry& entry)
{
    if (std::cout << "The entry " << entry; not entry.exists())
    {
        std::cout << " does not exists on the file system\n";
        return;
    }
    std::cout << " is ";
    if (entry.is_directory())
        std::cout << "a directory\n";
    if (entry.is_regular_file())
        std::cout << "a regular file\n";
    /*...*/
}

int main()
{
    std::filesystem::current_path(std::filesystem::temp_directory_path());

    std::filesystem::directory_entry
       entry{std::filesystem::current_path()};
    print_entry_info(entry);

    std::filesystem::path name{"cppreference.html"};
    std::ofstream{name} << "C++";

    std::cout << "entry.assign();\n";
    entry.assign(entry/name);
    print_entry_info(entry);

    std::cout << "remove(entry);\n";
    std::filesystem::remove(entry);
    print_entry_info(entry); // the entry still contains old "state"

    std::cout << "entry.assign();\n";
    entry.assign(entry); // or just call entry.refresh()
    print_entry_info(entry);
}

🌈 Possible output: 🌈

The entry "/tmp" is a directory
entry.assign();
The entry "/tmp/cppreference.html" is a regular file
remove(entry);
The entry "/tmp/cppreference.html" is a regular file
entry.assign();
The entry "/tmp/cppreference.html" does not exists on the file system

👑 See also 👑

• operator= — assigns contents (public member function)

source/version and date: http://cppreference.com · 2024.06.10 · std::filesy...try::assign(3) — bye bestie, go assign with main character energy 💅✨