difftime返回值的机关是秒吗

difftime返回值的单位是秒吗？

C/C++ code

#include "stdlib.h"#include "time.h"int main(void){    time_t first, second;    first = time(NULL);    second = time(NULL);    printf("%f", difftime(second, first));        return 0;}

C/C++ code

#include <time.h>#include <stdio.h>int main(void){    time_t first, second;    first = time(NULL); /* Gets system time */    sleep(2); /* Waits 2 secs */    second = time(NULL); /* Gets system time again */    printf("The difference is: %f seconds\n",difftime(second,first));    return 0;}[root@bogon temp]# ./t1The difference is: 2.000000 seconds测试证明，返回的是秒