[C/C++标准库]_[初级]_[转换UTC时间到local本地时间]

场景

1.如果有面向全球用户的网站, 一般在存储时间数据时存储的是UTC格式的时间, 这样时间是统一的, 并可以根据当地时区来进行准确的转换.

2.存储本地时间的问题就在于如果换了时区, 那么显示的时间并不正确. 所以我们存储时间时最好还是存储UTC时间,便于正确的转换.

说明

1.C/C++标准库提供了标准函数可以转换, 不需要借助Win32 API.

例子

// test_datetime_format.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <time.h>
#include <sstream>
#include <iostream>
#include <assert.h>

//2014-09-13T10:52:36Z
//2014-09-13 10:52:36
char* ConvertUtcToLocalTime(struct tm* t2,const char* date){

    struct tm t;
    memset(&t,0,sizeof(t));
    t.tm_year = atoi(date)-1900;
    t.tm_mon = atoi(date+5)-1;
    t.tm_mday = atoi(date+8);
    t.tm_hour = atoi(date+11);
    t.tm_min = atoi(date+14);
    t.tm_sec = atoi(date+17);

    time_t tt = _mkgmtime64(&t);
    if(tt != -1){
        if(t2 == NULL){
            t2 = &t;
        }
        *t2 = *localtime(&tt);
        char* ds = (char*) malloc(24);
        memset(ds, 0, 24);
        sprintf(ds, "%.4d-%.2d-%.2d %.2d:%.2d:%.2d", t2->tm_year + 1900,
                t2->tm_mon + 1, t2->tm_mday, t2->tm_hour, t2->tm_min,
                t2->tm_sec);
        return ds;
    }
    return NULL;
}

//https://www.w3.org/TR/NOTE-datetime
//https://msdn.microsoft.com/en-us/library/2093ets1.aspx
//2014-09-13T10:52:36Z
int _tmain(int argc, _TCHAR* argv[])
{
    const char* kTime = "2014-09-13 18:52:36";
    std::cout << "Source DateTime: " << "2014-09-13T10:52:36Z" << std::endl;
    auto t = ConvertUtcToLocalTime(NULL,"2014-09-13T10:52:36Z");
    std::cout << "Dest DateTime: " << t << std::endl;
    assert(!strcmp(t,kTime));

    t = ConvertUtcToLocalTime(NULL,"2014-09-13 10:52:36");
    std::cout << t << std::endl;
    assert(!strcmp(t,kTime));

    struct tm tt;
    t = ConvertUtcToLocalTime(&tt,"2014-09-13 10:52:36");
    std::cout << t << std::endl;
    assert(!strcmp(t,kTime));
    assert(tt.tm_year == (2014-1900));
    assert(tt.tm_mon == 9-1);
    assert(tt.tm_mday == 13);
    assert(tt.tm_hour == 18);
    assert(tt.tm_min == 52);
    assert(tt.tm_sec == 36);

    return 0;
}

}

输出

Source DateTime: 2014-09-13T10:52:36Z
Dest DateTime: 2014-09-13 18:52:36
2014-09-13 18:52:36
2014-09-13 18:52:36

参考

NOTE-datetime

_mkgmtime

timegm - Linux man page

Converting Between Local Times and GMT/UTC in C/C++