3

I'm writing a C++ application that needs to be portable between at least Ubuntu 15, FreeBSD 11, MacOS X and Windows 7 (compiled with GCC, clang and MSVC). All of these systems have a notion of a file with at least a modification date/time.

The question is: is there a way to set a file modification time using a single piece of C++ code that would work on all of these systems?

NB: By setting the file modification time I mean setting it to any specified value, not the current time (i.e. not the touch functionality).

rustyx
  • 80,671
  • 25
  • 200
  • 267
  • 5
    I hate to say, but you can do it with boost. – Nick Mar 23 '16 at 13:17
  • In pure c++ it can't be done – DimChtz Mar 23 '16 at 13:18
  • 1
    Read the file and write it back. – Zereges Mar 23 '16 at 13:23
  • You can use Boost.Filesystem, or simply `#ifdef _WIN32 ... #else ... #endif` because apart from Windows all those others support the POSIX APIs such as [`utimes()`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/utimes.html). There's no difference between GNU/Linux, BSD and OS X in this respect, although GNU and newer FreeBSD might also support the higher-resolution `futimens` function. – Jonathan Wakely Mar 23 '16 at 16:30

2 Answers2

7

With boost::filesystem, you can use this function to get/set the time: 

void last_write_time(const path& p, const std::time_t new_time);

This is also available on some compilers as experimental feature on some compiles such as gcc or msvc. These use same API but different experimental namespace. So if you don't want to use boost, and as long as it's not yet integrated in the standard, you could make it portable with conditional compilation and using statement.

Community
  • 1
  • 1
Christophe
  • 68,716
  • 7
  • 72
  • 138
4

The C++ Standard Library does not (yet) have any notion of file (until filesystem will become part of the Standard Library, which may happen with C++17). At the moment, you need to rely on some cross-platform library such as boost::filesystem or Qt.

Claudio
  • 10,614
  • 4
  • 31
  • 71