std::experi..._write_time(3)

✨ NAME ✨

okay so bestie, welcome to the std::experimental::filesystem::last_write_time page from the C++ Standard Libary manual, section 3 💅

std::experimental::filesystem::last_write_time — std::experimental::filesystem::last_write_time. Like, yes, the NAME section is literally the same thing twice with a dash, and honestly? iconic. 🎀

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🌸 Synopsis 🌸

Defined in header <experimental/filesystem>:

file_time_type last_write_time( const path& p );                 (1)
(filesystem TS)
file_time_type last_write_time( const path& p, error_code& ec )
void last_write_time( const path& p, file_time_type new_time );
void last_write_time( const path& p, file_time_type new_time,    (2)
(filesystem TS)
error_code& ec );

1. Returns the time of the last modification of p, determined as if by accessing the member st_mtime of the POSIX stat (symlinks are followed). The non-throwing overload returns file_time_type::min() on errors.
2. Changes the time of the last modification of p, as if by POSIX futimens (symlinks are followed).

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💖 Parameters 💖

• p — path to examine or modify
• new_time — new modification time
• ec — out-parameter for error reporting in the non-throwing overload

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🎀 Return value 🎀

1. The time of the last modification of p.
2. (none)

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🚨 Exceptions 🚨

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. 🫶

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📝 Notes 📝

It is not guaranteed that immediately after setting the write time, the value returned by (1) is the same as what was passed as the argument to (2) because the file system's time may be more granular than file_time_type. no cap, time granularity is out here doing its own thing. 😭

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🧪 Example 🧪

// Run this code

#include <chrono>
#include <experimental/filesystem>
#include <fstream>
#include <iomanip>
#include <iostream>
namespace fs = std::experimental::filesystem;
using namespace std::chrono_literals;

int main()
{
    fs::path p = fs::current_path() / "example.bin";
    std::ofstream(p.c_str()).put('a'); // create file
    auto ftime = fs::last_write_time(p);

    std::time_t cftime = decltype(ftime)::clock::to_time_t(ftime); // assuming system_clock
    std::cout << "File write time is " << std::asctime(std::localtime(&cftime)) << '\n';

    fs::last_write_time(p, ftime + 1h); // move file write time 1 hour to the future
    ftime = fs::last_write_time(p); // read back from the filesystem

    cftime = decltype(ftime)::clock::to_time_t(ftime);
    std::cout << "File write time is " << std::asctime(std::localtime(&cftime)) << '\n';
    fs::remove(p);
}

💫 Possible output 💫

File write time is Tue Mar 31 19:47:04 2015

File write time is Tue Mar 31 20:47:04 2015

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🌈 See also 🌈

• file_time_type represents file time values (typedef)

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💅 Categories 💅

• Noindexed pages
• unconditionally noexcept

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🫶 Hidden categories 🫶

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

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mwah 💋 that's the whole page, bestie — source is http://cppreference.com, date/version is 2024.06.10, and the footer manual title was std::experi..._write_time(3) (yes, truncated exactly like that). 🎀✨🦋