mktime return "-1" "+8"等示例

c/c++中使用mktime时，有时候会返回-1错误，主要的原因是输入了非法值，下面是一些常用的示例

#include <bits/stdc++.h>
#include <ctime>
#include <cstdio>
using namespace std;
//g++ mktime.cpp -std=c++11 -o mktime
int main(int argc, char* argv[])
{
    cout<<"mktime example"<<endl;
    struct tm stm;
    stm.tm_sec = 0;
    stm.tm_min = 0;
    stm.tm_hour = 0;
    stm.tm_mday = 1;
    stm.tm_mon = 0;
    stm.tm_year = 70;
    time_t ret;
    setenv("TZ","Etc/GMT",1);
    tzset();
    ret = mktime(&stm);
    printf("Etc/GMT ret = %ld\n", ret);
    setenv("TZ","Europe/Berlin",1);
    tzset();
    ret = mktime(&stm);
    printf("UTC+01:00 ret = %ld\n", ret);
    setenv("TZ","Atlantic/Azores",1);
    tzset();
    ret = mktime(&stm);
    printf("UTC-01:00 ret = %ld\n", ret);
    setenv("TZ","Asia/Shanghai",1);
    tzset();
    ret = mktime(&stm);
    printf("Asia/Shanghai ret = %ld\n", ret);
}

编译，运行，结果

g++ mktime.cpp -std=c++11 -o mktime
./mktime
mktime example
Etc/GMT ret = 0
UTC+01:00 ret = -3600
UTC-01:00 ret = 3600
Asia/Shanghai ret = -28800

Referenced from:https://jp.cybozu.help/general/zh/admin/list_systemadmin/list_localization/timezone.html

需要注意的是：
time():返回自00:00:00 UTC, January 1, 1970到現在所經過的秒數,注意,是UTC，中文默认时间是CST，也是UTC+08:00

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