C + + timestamp conversion (related to GMT CST time zone conversions)

Origin of the problem

Timestamp conversion (timestamp: The total number of seconds from January 1, 1970 (00:00:00) to the current time. ）

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

int main(int argc, const char * argv[])
{    
    time_t t;
    struct tm *p;
    t=1408413451;
    p=gmtime(&t);
    char s[80];
    strftime(s, 80, "%Y-%m-%d %H:%M:%S", p);
    printf("%d: %s\n", (int)t, s);
}

Results

1408413451      2014-08-19 01:57:1408384651

However, the results of using the command on the Linux terminal differ

 
[###t]$ date -d @1408413451
Tue Aug 19 09:57:31 CST 2014

By comparison, the two are just 8 hours, CST means Greenwich Mean time, through the strftime () function can output timezone, correct the following

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

int main(int argc, const char * argv[])
{    
    time_t t;
    struct tm *p;
    t=1408413451;
    p=gmtime(&t);
    char s[80];
    strftime(s, 80, "%Y-%m-%d %H:%M:%S::%Z", p);
    printf("%d: %s\n", (int)t, s);
}

Results

1408413451:2014-08-19 01:57:31::GMT

Bottom

GMT (Greenwich Mean time) represents GMT. In 17th century, the Royal Observatory of Greenwich was observing astronomical objects for the expansion of its naval hegemony. The old Royal Observatory was formally established in 1675, using the Meridian of Greenwich to divide the Earth's two hemispheres by longitude 0 degrees. There is a sign on the wall of the observatory 24 Hour clock, showing the current time, for the world, the time set here is the world time reference point, the whole world in Greenwich time as standard to set the time, this is our familiar "Greenwich Standard Time" (Greenwich Mean Times , referred to as g.m.t.) The origin.

CST can also represent the following 4 different time zones:

Central Standard Time (USA) UT-6:00
Central Standard Time (Australia) UT+9:30
China Standard Time UT+8:00
Cuba Standard Time UT-4:00

It can be seen that CST could also represent the standard time in four countries of the United States, Australia, China, and Cuba.

Okay, the difference between the two is 8 hours (CST than GMT late/large 8 hours), GMT+8*3600=CST, the code is as follows

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

int main(int argc, const char * argv[])
{    
    time_t t;
    struct tm *p;
    t=1408413451;
    p=gmtime(&t);
    char s[80];
    strftime(s, 80, "%Y-%m-%d %H:%M:%S::%Z", p);
    printf("%d: %s\n", (int)t, s);

    t=1408413451 + 28800;
    p=gmtime(&t);
    strftime(s, 80, "%Y-%m-%d %H:%M:%S", p);
    printf("%d: %s\n", (int)t, s);
    return 0;
}

Results

1408413451: 2014-08-19 01:57:31::GMT
1408442251: 2014-08-19 09:57:31

Linux Platforms

Tue 09:57:31 CST 2014