difftime

double difftime( time_t time_end, time_t time_beg );

Computes difference between two calendar times as time_t objects (time_end - time_beg) in seconds. If time_end refers to time point before time_beg then the result is negative.

Parameters

Return value

Difference between two times in seconds.

Notes

On POSIX systems, time_t is measured in seconds, and difftime is equivalent to arithmetic subtraction, but C and C++ allow fractional units for time_t.

Example

#include <stdio.h>
#include <time.h>
 
int main(void)
{
    time_t now = time(0);
 
    struct tm beg = *localtime(&now);
 
    // set beg to the beginning of the month
    beg.tm_hour = 0,
    beg.tm_min = 0,
    beg.tm_sec = 0,
    beg.tm_mday = 1;
 
    double seconds = difftime(now, mktime(&beg));
 
    printf("%.f seconds have passed since the beginning of the month.\n", seconds);
 
    return 0;
}

1937968 seconds have passed since the beginning of the month.

References

• C17 standard (ISO/IEC 9899:2018):
• 7.27.2.2 The difftime function (p: 285)
• C11 standard (ISO/IEC 9899:2011):
• 7.27.2.2 The difftime function (p: 390)
• C99 standard (ISO/IEC 9899:1999):
• 7.23.2.2 The difftime function (p: 338)
• C89/C90 standard (ISO/IEC 9899:1990):
• 7.12.2.2 The difftime function (p: 171)

See also