计算时差

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 );

可用于计算某段程序的运行时间