//函数原型 int nanosleep(struct timespec *req, struct timespec *rem)//参数列表：//  req:要求的睡眠时间//  rem:剩余的睡眠时间//返回值：//  0：成功；-1，失败，errno保存错误代码//目的：纳秒级别的延迟int nano_delay(long delay){    struct timespec req, rem;    long nano_delay = delay;    int ret = 0;    while(nano_delay > 0)    {            rem.tv_sec = 0;            rem.tv_nsec = 0;            req.tv_sec = 0;            req.tv_nsec = nano_delay;            if(ret = (nanosleep(&req, &rem) == -1))            {                printf("nanosleep failed.\n");                            }            nano_delay = rem.tv_nsec;    };    return ret;}//测试，纳秒级延迟的误差率int main(){    int ret = 0;    long delay = 0;    struct timespec start, end, interv;    for(delay = 1000; delay < 1000*1000; delay+=1000)    {           curr_time(&start);        nano_delay(delay);        curr_time(&end);        diff(&start, &end, &interv);        printf("delay = %ld, real delay = %ld, error = %g.\n", delay, interv.tv_sec * 1000000000 + interv.tv_nsec, (float)(interv.tv_sec * 1000000000 + interv.tv_nsec - delay)/delay );    }}//测试结果：//  Duo CPU e8200//  Ubuntu 12.10 Kernel 3.4//