p7-6.c

UNIX程序设计教程

#include <stdio.h>
#include <sys/types.h>
#include <sys/times.h>
#include <unistd.h>
#include <sys/time.h>
void work();
int main (void)
{
    struct timeval start, stop,diff;
    double total_sec;
    clock_t b,e,t;
    struct tms buf;
    gettimeofday(&start,NULL);  
    work(5);     /* 程序7－2中的work函数 */ 
    gettimeofday(&stop,NULL);
    timeval_subtract(&diff,&stop, &start);
    total_sec = (double)(diff.tv_sec*1000000+diff.tv_usec)
                /(double)1000000;
    printf("tatol wall time : %lf seconds\n",total_sec);
    return 0;
}
/* 类型为'struct timeval'的两个对象x和y相减,存储结果于result。
   若差为负数,返回1,否则返回0.*/
int timeval_subtract(struct timeval *result, 
                     struct timeval *x, struct timeval *y)
{
    if (x->tv_usec < y->tv_usec) {
        int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
        y->tv_usec -= 1000000 * nsec;
        y->tv_sec += nsec;
    }
    if (x->tv_usec - y->tv_usec > 1000000) {
       int nsec = (y->tv_usec - x->tv_usec) / 1000000;
       y->tv_usec += 1000000 * nsec;
       y->tv_sec -= nsec;
    }
    result->tv_sec = x->tv_sec - y->tv_sec;
    result->tv_usec = x->tv_usec - y->tv_usec;
    /* 若结果为负则返回1 */
return x->tv_sec < y->tv_sec;
}
void work(int k)       /* 模拟工作 */
{
    FILE *f;
    int i;
    double x=4.5;
    f = tmpfile();
    for(i = 0; i < k*100000; i++){
        fprintf(f,"Do some output\n");
        if(ferror(f)){
            fprintf(stderr,"Error writing to temorary file\n");
            exit(1);
        }
    }
    for(i=0;i<k*100000;i++)
        x=log(x*x+3.21);
}