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;
}