Calculates the wall-clock time used by the calling process.

clock_t clock( void );

The elapsed wall-clock time since the start of the process (elapsed time in seconds times CLOCKS_PER_SEC). If the amount of elapsed time is unavailable, the function returns –1, cast as a clock_t.

The clock function tells how much wall-clock time the calling process has used. Note that this is not strictly conformant with ISO C99, which specifies net CPU time as the return value. To obtain CPU time, use the Win32 GetProcessTimes function.

A timer tick is approximately equal to 1/CLOCKS_PER_SEC seconds. Given enough time, the value returned by clock can exceed the maximum positive value of clock_t and become negative, or exceed the maximum absolute value and roll over. Do not rely on this value for total elapsed time in processes that run for more than 214,748 seconds, or about 59 hours.



Required header



For additional compatibility information, see Compatibility in the Introduction.


// crt_clock.c
// This example prompts for how long
// the program is to run and then continuously
// displays the elapsed time for that period.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void sleep( clock_t wait );

int main( void )
   long    i = 6000000L;
   clock_t start, finish;
   double  duration;

   // Delay for a specified time.
   printf( "Delay for three seconds\n" );
   sleep( (clock_t)3 * CLOCKS_PER_SEC );
   printf( "Done!\n" );

   // Measure the duration of an event.
   printf( "Time to do %ld empty loops is ", i );
   start = clock();
   while( i-- ) 
   finish = clock();
   duration = (double)(finish - start) / CLOCKS_PER_SEC;
   printf( "%2.1f seconds\n", duration );

// Pauses for a specified number of milliseconds.
void sleep( clock_t wait )
   clock_t goal;
   goal = wait + clock();
   while( goal > clock() )
Delay for three seconds
Time to do 6000000 empty loops is 0.1 seconds

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.