C语言时间

#include <stdio.h>
#include <sys/time.h>
#include <stdlib.h>
#include <time.h>
#include <limits.h>

void timevalfunction(){
    unsigned i = 0;
    struct timeval start, end;
    gettimeofday(&start, NULL);
    for(i = 0;i < UINT32_MAX; i++);
    gettimeofday(&end, NULL);
    unsigned long duration = (end.tv_sec - start.tv_sec) * 1000000 + end.tv_usec - start.tv_usec;
    printf("%luμs\n",duration);
}
void clockfunction(){
    unsigned i = 0;
    clock_t start, finish;
    start = clock();
    for(i = 0;i < UINT32_MAX; i++);
    finish = clock();
    unsigned long duration = finish - start;
    printf( "%luμs\n", duration);
}
void timespecfunction(){
    unsigned i = 0;
    struct timespec start, end;
    clock_gettime(CLOCK_REALTIME, &start);
    for(i = 0;i < UINT32_MAX; i++);
    clock_gettime(CLOCK_REALTIME, &end);
    unsigned long duration = (end.tv_sec - start.tv_sec) * 1000000000 + end.tv_nsec-start.tv_nsec;
    printf("%luns\n", duration);
}
int main(int argc, const char * argv[]) {
    timevalfunction();
    clockfunction();
    timespecfunction();

    return 0;
}

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