< cpp‎ | chrono‎ | c
Defined in header <ctime>
double difftime( std::time_t time_end, std::time_t time_beg );

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


[edit] Parameters

time_beg, time_end - times to compare

[edit] Return value

Difference between two times in seconds.

[edit] Notes

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

[edit] Example

#include <iostream>
#include <ctime>
int main()
    std::time_t start = std::time(NULL);
    volatile double d;
    // some time-consuming operation
    for (int n=0; n<10000; ++n) {
        for (int m=0; m<100000; ++m) {
           d += d*n*m;
    std::cout << "Wall time passed: "
              << std::difftime(std::time(NULL), start) << " s.\n";


Wall time passed: 7 s.

[edit] See also

a time interval
(class template)
C documentation for difftime