strptime() equivalent on Windows?

Is there a good equivalent implementation of strptime() available for Windows? Unfortunately, this POSIX function does not appear to be available.

Open Group description of strptime - summary: it converts a text string such as "MM-DD-YYYY HH:MM:SS" into a tm struct, the opposite of strftime().

Solution 1:

If you don't want to port any code or condemn your project to boost, you can do this:

1. parse the date using sscanf
2. then copy the integers into a struct tm (subtract 1 from month and 1900 from year -- months are 0-11 and years start in 1900)
3. finally, use mktime to get a UTC epoch integer

Just remember to set the isdst member of the struct tm to -1, or else you'll have daylight savings issues.

Solution 2:

Assuming you are using Visual Studio 2015 or above, you can use this as a drop-in replacement for strptime:

#include <time.h>
#include <iomanip>
#include <sstream>

extern "C" char* strptime(const char* s,
                          const char* f,
                          struct tm* tm) {
  // Isn't the C++ standard lib nice? std::get_time is defined such that its
  // format parameters are the exact same as strptime. Of course, we have to
  // create a string stream first, and imbue it with the current C locale, and
  // we also have to make sure we return the right things if it fails, or
  // if it succeeds, but this is still far simpler an implementation than any
  // of the versions in any of the C standard libraries.
  std::istringstream input(s);
  input.imbue(std::locale(setlocale(LC_ALL, nullptr)));
  input >> std::get_time(tm, f);
  if (input.fail()) {
    return nullptr;
  }
  return (char*)(s + input.tellg());
}

Just be aware that for cross platform applications, std::get_time wasn't implemented until GCC 5.1, so switching to calling std::get_time directly may not be an option.

Solution 3:

An open-source version (BSD license) of strptime() can be found here: http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/time/strptime.c?rev=HEAD

You'll need to add the following declaration to use it:

char *strptime(const char * __restrict, const char * __restrict, struct tm * __restrict);