c++ - why gmtime and localtime give me the same result? -

i have following test code see difference between gmtime , localtime. give me same result: utc:2013-05-02t13:59:58 local:2013-05-02t13:59:58

time_t now; time(&now); tm *ptimestruct = gmtime(&now); tm *plocaltimestruct = localtime(&now);  string timestr = ""; char timebuf[64] = {'\0'};  sprintf(timebuf,"utc:%-4.4d-%-2.2d-%-2.2dt%-2.2d:%-2.2d:%-2.2d "     "local:%-4.4d-%-2.2d-%-2.2dt%-2.2d:%-2.2d:%-2.2d",     (ptimestruct->tm_year + 1900),     (ptimestruct->tm_mon + 1),     ptimestruct->tm_mday,     ptimestruct->tm_hour,     ptimestruct->tm_min,     ptimestruct->tm_sec,     (plocaltimestruct->tm_year + 1900),     (plocaltimestruct->tm_mon + 1),     plocaltimestruct->tm_mday,     plocaltimestruct->tm_hour,     plocaltimestruct->tm_min,     plocaltimestruct->tm_sec);  timestr += timebuf; cout << timestr << endl; 

edit:

i in eastern time zone.

edit2:

updated code use diff struct, got same result:

        time_t now;         time(&now);         time_t now2;         time(&now2);         tm *ptimestruct = gmtime(&now);         tm *plocaltimestruct = localtime(&now2); 

you need copy values between calls gmtime , localtime:

the return value points statically allocated struct might overwritten subsequent calls of date , time functions.

says man page on system. that's common behaviour @ least on linux.