clock


clock

Obtains the CPU time used by the process

 #include <time.h> clock_t clock( void ); 

If you want to know how much CPU time your program has used, call the clock( ) function. The function's return type, clock_t, is defined in time.h as long. If the function returns -1, then the CPU time is not available. Note that the value of clock( ) does not reflect actual elapsed time, as it doesn't include any time the system may have spent on other tasks.

The basic unit of CPU time, called a "tick," varies from one system to another. To convert the result of the clock( ) call into seconds, divide it by the constant CLOCKS_PER_SEC, which is also defined in time.h.

Example

 #include <stdio.h> #include <time.h> time_t start, stop; clock_t ticks; long count; int main( ) {   time(&start);   for (count = 0; count <= 50000000; ++count)   {     if (count % 1000000 != 0) continue;   /* measure only full millions */     ticks = clock( );     printf("Performed %ld million integer divisions; "            "used %0.2f seconds of CPU time.\n",  count / 1000000,            (double)ticks/CLOCKS_PER_SEC);   }   time(&stop);   printf("Finished in about %.0f seconds.\n", difftime(stop, start));   return 0; } 

This program produces 51 lines of output, ending with something like this:

 Performed 50 million integer divisions; used 2.51 seconds of CPU time. Finished in about 6 seconds. 

See Also

time( ), difftime( )



C(c) In a Nutshell
C in a Nutshell (In a Nutshell (OReilly))
ISBN: 0596006977
EAN: 2147483647
Year: 2006
Pages: 473

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