clock

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Contents
  1. INTERFACE
  2. DESCRIPTION
  3. RETURN VALUES
  4. STANDARDS

determine processor time used

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Computing C Time.h

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INTERFACE

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

DESCRIPTION

The clock function determines the amount of processor time used since the invocation of the calling process, measured in CLOCKS_PER_SEC of a second.

The code below counts the number of seconds that passed while running some for loop.

Example 1
Workings

\code #include <stdio.h> #include <time.h> #include <math.h> int main() { clock_t start = clock(); for (long i = 0; i < 100000000; ++i) exp(log((double)i)); clock_t finish = clock(); printf("It took %d seconds to execute the for loop.
", (finish - start) / CLOCKS_PER_SEC); return 0; } \endcode

Solution

Output:

It took 23 seconds to execute the for loop.

RETURN VALUES

The clock function returns the amount of time used unless an error occurs, in which case the return value is -1.

STANDARDS

The clock function conforms to ISO/IEC 9899:1990 ("ISO C90"). However, version 2 of the Single UNIX Specification ('SUSv2') CLOCKS_PER_SEC to be defined as one million. FreeBSD does not conform to this requirement; changing the value would introduce binary incompatibility and one million is still inadequate on modern processors.