北京时间比格林威治早8个小时，思路是先将北京时间转换为距1970年1月1日0点的秒数，然后在转换成服务器本地时区的格林威治时间。

例子程序 gmttime.c：

#include

#include

#include

#include

int main(void)

{

printf("--------------\n");

char ori_time[14+1];

char tmp_year[4+1];

char tmp_month[2+1];

char tmp_day[2+1];

char tmp_hour[2+1];

char tmp_min[2+1];

char tmp_sec[2+1];

char sCurrentTime[15];

struct tm tmCurrentTime, *gmCurrentTime;

time_t gmt;

memset(ori_time, 0x00, sizeof(ori_time));

memset(tmp_year, 0x00, sizeof(tmp_year));

memset(tmp_month, 0x00, sizeof(tmp_month));

memset(tmp_day, 0x00, sizeof(tmp_day));

memset(tmp_hour, 0x00, sizeof(tmp_hour));

memset(tmp_min, 0x00, sizeof(tmp_min));

memset(tmp_sec, 0x00, sizeof(tmp_sec));

memset(sCurrentTime, 0x00, sizeof(sCurrentTime));

memcpy(ori_time, "20170225132901", 14);

printf("ori_time: %s\n", ori_time);

//取年

memcpy(tmp_year, ori_time, 4);

printf("year: %s\n", tmp_year);

tmCurrentTime.tm_year = atoi(tmp_year);

tmCurrentTime.tm_year = tmCurrentTime.tm_year - 1900;

//取月

memcpy(tmp_month, ori_time+4, 2);

printf("month: %s\n", tmp_month);

tmCurrentTime.tm_mon = atoi(tmp_month);

tmCurrentTime.tm_mon = tmCurrentTime.tm_mon - 1;

//取日

memcpy(tmp_day, ori_time+6, 2);

printf("day: %s\n", tmp_day);

tmCurrentTime.tm_mday = atoi(tmp_day);

//取时

memcpy(tmp_hour, ori_time+8, 2);

printf("hour: %s\n", tmp_hour);

tmCurrentTime.tm_hour = atoi(tmp_hour);

//取分

memcpy(tmp_min, ori_time+10, 2);

printf("min: %s\n", tmp_min);

tmCurrentTime.tm_min = atoi(tmp_min);

//取秒

memcpy(tmp_sec, ori_time+12, 2);

printf("sec: %s\n", tmp_sec);

tmCurrentTime.tm_sec = atoi(tmp_sec);

//转换为秒

gmt = mktime(&tmCurrentTime); //time_t 转换为 tm

//转换为格林威治时间

gmCurrentTime = gmtime(&gmt); //tm 转换为 time_t

sprintf(sCurrentTime, "%4d%02d%02d%02d%02d%02d",

gmCurrentTime->tm_year + 1900, gmCurrentTime->tm_mon + 1,

gmCurrentTime->tm_mday, gmCurrentTime->tm_hour,

gmCurrentTime->tm_min, gmCurrentTime->tm_sec);

printf("gmt_time: %s\n", sCurrentTime);

printf("--------------\n");

return 0;

}

其中mktime将时间转换为秒数，gmtime将秒数转换为服务器本地时区对应的格林威治时间。