std::filesystem::last_write_time

Defined in header `<filesystem>`
std::filesystem::file_time_type last_write_time(const std::filesystem::path& p); std::filesystem::file_time_type last_write_time(const std::filesystem::path& p, std::error_code& ec)	(1)	(since C++17)
void last_write_time(const std::filesystem::path& p, std::filesystem::file_time_type new_time); void last_write_time(const std::filesystem::path& p, std::filesystem::file_time_type new_time, std::error_code& ec);	(2)	(since C++17)

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)

Parameters

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

Return value

1) The time of the last modification of p

2) (none)

Exceptions

The overload that does not take a std::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 a std::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

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.

Example

Run this code

#include <iostream>
#include <chrono>
#include <iomanip>
#include <fstream>
#include <filesystem>
namespace fs = std::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

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications