strptime() equivalent on Windows?

Question

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().

Answer 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.

Answer 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.

Answer 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);

Answer 4

This does the job:

#include "stdafx.h"
#include "boost/date_time/posix_time/posix_time.hpp"
using namespace boost::posix_time;

int _tmain(int argc, _TCHAR* argv[])
{
    std::string ts("2002-01-20 23:59:59.000");
    ptime t(time_from_string(ts));
    tm pt_tm = to_tm( t );

Notice, however, that the input string is YYYY-MM-DD

Answer 5

This is a copy-and-paste-capable C example of the answer @amwinter posted, although I did not use sscanf() - the *scanf() family of functions is IMO too perverse to do robust parsing with:

(headers and error checking omitted to keep the example short enough to prevent a vertical scroll bar from getting created)

    // format will be YYYYmmddHHMMSSZ
    const char *notAfter = getNotAfterStringFromX509Cert( x509 );
    struct tm notAfterTm = { 0 };

#ifdef _WIN32
    char buffer[ 8 ];

    memset( buffer, 0, sizeof( buffer ) );
    strncpy( buffer, notAfter, 4 );
    notAfterTm.tm_year = strtol( buffer, NULL, 10 ) - 1900;

    memset( buffer, 0, sizeof( buffer ) );
    strncpy( buffer, notAfter + 4, 2 );
    notAfterTm.tm_mon = strtol( buffer, NULL, 10 ) - 1;

    memset( buffer, 0, sizeof( buffer ) );
    strncpy( buffer, notAfter + 6, 2 );
    notAfterTm.tm_mday = strtol( buffer, NULL, 10 );

    memset( buffer, 0, sizeof( buffer ) );
    strncpy( buffer, notAfter + 8, 2 );
    notAfterTm.tm_hour = strtol( buffer, NULL, 10 );

    memset( buffer, 0, sizeof( buffer ) );
    strncpy( buffer, notAfter + 10, 2 );
    notAfterTm.tm_min = strtol( buffer, NULL, 10 );

    memset( buffer, 0, sizeof( buffer ) );
    strncpy( buffer, notAfter + 12, 2 );
    notAfterTm.tm_sec = strtol( buffer, NULL, 10 );

    time_t result = mktime( &notAfterTm );

This is a really simple case, where the input string is in a format known exactly, so it's extremely easy to parse.

Answer 6

One alternative is to use GetSystemTime and send the time information to a function that parses it according to your format using vsnprintf_s. In the example below there is one function that creates a time string with milli second precision. It then sends the string to a function that formats it according to the desired format:

#include <string>
#include <cstdio>
#include <cstdarg>
#include <atlstr.h> 

std::string FormatToISO8601 (const std::string FmtS, ...) {
   CStringA BufferString;
   try {
       va_list VaList;
       va_start (VaList, FmtS);
       BufferString.FormatV (FmtS.c_str(), VaList);
   } catch (...) {}
   return std::string (BufferString);
}

void CreateISO8601String () {
   SYSTEMTIME st;
   GetSystemTime(&st);
   std::string MyISO8601String = FormatToISO8601 ("%4u-%02u-%02uT%02u:%02u:%02u.%03u", st.wYear, st.wMonth, st.wDay, st.wHour, st.wMinute, st.wSecond, st.wMilliseconds);
}

Answer 7

There is a version of strptime() for windows available at https://github.com/p-j-miller/date-time . The same location includes a matching strftime() function and a comprehensive test program. This also works under Linux if you need to create code that works on both OS's.