计算程序中某一个函数或算法的执行时间
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
int main()
{
long i = 10000000L;
clock_t start, finish;
double duration;
printf( "Time to do %ld empty loops is ", i) ;
start = clock();
while( i-- );
finish = clock();
duration = (double)(finish - start) / CLOCKS_PER_SEC;
printf( "%f seconds\n", duration );
return 0;
}