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Updated: July 2009

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 time the calling process has used. A timer tick is approximately equal to 1/CLOCKS_PER_SEC second.


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 Done! Time to do 6000000 empty loops is 0.1 seconds

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




July 2009

Removed obsolete information.

Information enhancement.

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