The C library functions to measure computational time.


The clock() function is of type clock_t (defined in time.h), therefore you need to include in your C program:

#include <time.h>

clock() returns the number of clock ticks of elapsed processor time (or -1 if there is an error). To know how many clock ticks are in one second, you need to use the macro CLOCKS_PER_SEC (defined also in time.h).

The standard procedure of using clock() is to take the differences between different time measurements, and divide them by CLOCKS_PER_SEC. Here is an example:

#include <time.h>

...

clock_t t1, t2;

t1 = clock();

...

/* operations you want to measure */

...

t2 = clock();

printf(" Timing is %f\n", (double)(t2-t1)/CLOCKS_PER_SEC );

...

Also, you can measure the computational time using the function gettimeofday defined in the header file of sys/time.h

#include <sys/time.h>

...

struct timeval start, end;

double diff;

...

gettimeofday(&start,0);

...

/* operations you want to measure */

...

gettimeofday(&end,0);

diff = (end.tv_sec - start.tv_sec) +

    (double)(end.tv_usec - start.tv_usec)/1e6;

printf("Timing is %g sec.\n", diff); 

...

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