NAME¶

std::experimental::filesystem::last_write_time - std::experimental::filesystem::last_write_time

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)

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 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 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 <experimental/filesystem>
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

See also¶

file_time_type represents file time values
(typedef)