获得本地时间并格式化为http需要的格式：比如（Date: Fri, 31 Dec 1999 23:59:59 GMT）

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>

char localtm[80];
void getlocaltime()
{
time_t now; //实例化time_t结构
struct tm *timenow; //实例化tm结构指针
time(&now);     //time函数读取现在的时间(国际标准时间非北京时间)，然后传值给now

timenow = localtime(&now);

char daytime[50];
asctime_r(timenow, daytime);

printf("%s", daytime);
char *pch, *week, *mon, *day, *time, *year;
pch = strtok(daytime, " ");
int i = 0;
while(pch != NULL)
{
printf("%s\n", pch);
switch(i)
{
case 0: week = pch; break;
case 1: mon = pch; break;
case 2: day = pch; break;
case 3: time = pch; break;
case 4: year = pch; break;
default: break;
}
pch = strtok(NULL, " ");
i++;
}

char realyear[4];
strncpy(realyear, year, 4);
//char localtime[80];
printf("Date: %s, %s %s %s %s GMT\n", week, day, mon, realyear, time);
sprintf(localtm, "Date: %s, %s %s %s %s GMT\n", week, day, mon, realyear, time);
//return localtime;
}