c语言获取系统时间跨平台方法及计算程序运行时间

void getCurrentDateTime(char* current_datetime)
{
    time_t nowtime;
    struct tm* timeinfo;
    time(&nowtime);
    timeinfo = localtime(&nowtime);
    int xtn = timeinfo->tm_year + 1900;
    xtn = xtn % 2000;
    int xty = timeinfo->tm_mon + 1;
    int xtr = timeinfo->tm_mday;
    int xts = timeinfo->tm_hour;
    int xtf = timeinfo->tm_min;
    int xtm = timeinfo->tm_sec;
    snprintf(current_datetime, 18, "%d-%d-%d %d:%d:%d", xtn, xty, xtr, xts, xtf, xtm);
}

char* current_datetime = malloc(18);
memset(current_datetime, 0, 18);
getCurrentDateTime(current_datetime);

计算程序的耗时

struct   timeval   start, stop, diff;
    gettimeofday(&start, 0);   //开始计时
    for (int i=0;i<100000;i++)
    {
        root = json_tokener_parse(json_str);  // 每次20us
        changes = json_object_object_get(root, "change");
    }
    gettimeofday(&stop, 0);   //结束计时
    timeval_subtract(&diff, &start, &stop);
    printf("总计用时:%d秒%d微秒\n",diff.tv_sec, diff.tv_usec);

int timeval_subtract(struct timeval* result, struct timeval* x, struct timeval* y)
{
    if (x->tv_sec > y->tv_sec)
        return -1;

    if ((x->tv_sec == y->tv_sec) && (x->tv_usec > y->tv_usec))
        return -1;

    result->tv_sec = (y->tv_sec - x->tv_sec);
    result->tv_usec = (y->tv_usec - x->tv_usec);

    if (result->tv_usec < 0)
    {
        result->tv_sec--;
        result->tv_usec += 1000000;
    }

    return 0;
}

 头文件time.h和sys/time.h的区别与关系