C时间函数

C的几个时间函数，写一段小代码，把其全部囊括。

#include <stdio.h>
#include <time.h>
#include <assert.h>

int main()
{
time_t now = time(NULL);
printf("now utc is %d\n", now);

struct tm* gtmie = gmtime(&now);
struct tm* ctmie = localtime(&now);
time_t now2 = mktime(gtmie );
time_t now3 = mktime(ctmie );
assert (now==now2);
assert (now==now3);

printf("Time now is %s\n", asctime(gtmie));
printf("Time now is %s\n", asctime(ctmie));
printf("Time now is %s\n", ctime(&now));

char buf[124];
size_t len;

len = strftime(buf,124,"%Y-%m-%d %H:%M:%S %Z",gtmie);
printf("Time now is %s\n",buf);

}