Calculates the difference between two arithmetic time values
#include <time.h> double difftime ( time_t time2 , time_t time1 );
The difftime( ) function returns the difference between two time values, time2 - time1, as a number of seconds. While difftime( ) has the return type double, its arguments have the type time_t. The time_t type is usually, but not necessarily, defined as an integer type such as long or unsigned long.
A common way to obtain the argument values passed to difftime( ) is by successive calls to the time( ) function, which returns the current time as a single arithmetic value.
See the sample program for clock( ) in this chapter.