在軟件設計中經常會用到關於時間的處理，用來計算語句、函數的執行時間，這時就需要精確到毫秒甚至是微妙的時間。
int gettimeofday(struct timeval *tv, struct timezone *tz);
int settimeofday(const struct timeval *tv , const struct timezone *tz);
struct timeval {
time_t tv_sec; /* seconds */
SUSEconds_t tv_usec; /* microseconds */
};
struct timezone {
int tz_minuteswest; /* minutes west of Greenwich */
int tz_dsttime; /* type of DST correction */
};
下面是個簡單的例子，用來統計程序的執行時間：
…
struct timeval t_start,t_end;
long cost_time = 0;
//get start time
gettimeofday(&t_start, NULL);
printf("Start time: %ld us", t_start.tv_usec);
//some operation
…
//get end time
gettimeofday(&t_end, NULL);
printf("End time: %ld us", t_end.tv_usec);
//calculate time slot
cost_time = t_end.tv_usec - t_start.tv_usec;
printf("Cost time: %ld us", cost_time);
…
輸出：
Start time: 438061 us
End time: 459867 us
Cost time: 21806 us