< cpp‎ | experimental‎ | fs
Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals TS v2)
Library fundamentals 3 (library fundamentals TS v3)
Extensions for parallelism (parallelism TS)
Extensions for parallelism 2 (parallelism TS v2)
Extensions for concurrency (concurrency TS)
Extensions for concurrency 2 (concurrency TS v2)
Concepts (concepts TS)
Ranges (ranges TS)
Reflection (reflection TS)
Mathematical special functions (special functions TR)
Defined in header <experimental/filesystem>
file_time_type last_write_time(const path& p);
file_time_type last_write_time(const path& p, error_code& ec)
(1) (filesystem TS)
void last_write_time(const path& p, file_time_type new_time);
void last_write_time(const path& p, file_time_type new_time, error_code& ec);
(2) (filesystem TS)
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)


[edit] Parameters

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

[edit] Return value

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

[edit] 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:  

[edit] 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.

[edit] Example

#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';

Possible output:

File write time is Tue Mar 31 19:47:04 2015
File write time is Tue Mar 31 20:47:04 2015

[edit] See also

represents file time values
(typedef) [edit]