Visual Studio 6.0

Calculates the processor time used by the calling process.

clock_t clock( void );

Routine Required Header Compatibility
clock <time.h> ANSI, Win 95, Win NT

For additional compatibility information, see Compatibility in the Introduction.


LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version

Return Value

clock returns the number of clock ticks of elapsed processor time. The returned value is the product of the amount of time that has elapsed since the start of a process and the value of the CLOCKS_PER_SEC constant. If the amount of elapsed time is unavailable, the function returns –1, cast as a clock_t.


The clock function tells how much processor time the calling process has used. The time in seconds is approximated by dividing the clock return value by the value of the CLOCKS_PER_SEC constant. In other words, clock returns the number of processor timer ticks that have elapsed. A timer tick is approximately equal to 1/CLOCKS_PER_SEC second. In versions of Microsoft C before 6.0, the CLOCKS_PER_SEC constant was called CLK_TCK.


/* 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 );

void main( void )
   long    i = 600000L;
   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 600000 empty loops is 0.1 seconds

Time Management Routines

See Also   difftime, time