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c++file-iolast-modified

C++ How to check the last modified time of a file

I'm caching some information from a file and I want to be able to check periodically if the file's content has been modified so that I can read the file again to get the new content if needed.

That's why I'm wondering if there is a way to get a file's last modified time in C++.

Solution

  • There is no language-specific way to do this, however the OS provides the required functionality. In a unix system, the stat function is what you need. There is an equivalent _stat function provided for windows under Visual Studio.

    So here is code that would work for both:

    #include <sys/types.h>
#include <sys/stat.h>
#ifndef WIN32
#include <unistd.h>
#endif

#ifdef WIN32
#define stat _stat
#endif

auto filename = "/path/to/file";
struct stat result;
if(stat(filename.c_str(), &result)==0)
{
    auto mod_time = result.st_mtime;
    ...
}