mktime issue

[afrogonabike]

Hi,

I'm trying to use the mktime function. In order to test I thought I'd try and get it to return time 0 i.e. 01/01/1970 00:00:00. The code I'm using is as follows:

struct tm timeinfo;
memset(&timeinfo,0,sizeof(timeinfo));
timeinfo.tm_hour = 0;
timeinfo.tm_min = 0;
timeinfo.tm_sec = 0;
timeinfo.tm_year = 70;
timeinfo.tm_mday = 1;
timeinfo.tm_mon = 0;
timeinfo.tm_isdst = 0;

std::cerr <<std::endl << mktime(&timeinfo) << std::endl;

The output i get is:

-3600

This is precisely one hour out. I have tried setting tm_isdst to -1,0 and 1 and get the same result!

Anyone any ideas?

Thanks,

Tim

[kbw]

I get zero. It could be a DST issue.

[afrogonabike]

I've tried setting tm_isdst to -1,0 and 1 which doesn't make any difference.

[kbw]

What platform and timezone are you?

I've used gcc under cygwin in GMT.

[afrogonabike]

Using gcc on a linux pc in GMT.

[kbw]

-3600 on gcc on FreeBSD amd64.

Interestingly enough, going the other way with:

#include <iostream>
#include <time.h>
#include <memory.h>

int main()
{
        struct tm timeinfo;
        memset(&timeinfo, 0, sizeof(timeinfo));

        timeinfo.tm_year = 70;
        timeinfo.tm_mday = 1;
        std::cout << mktime(&timeinfo) << std::endl;

        time_t t = 0;
        struct tm *tm2 = localtime(&t);
        std::cout << mktime(tm2) << std::endl;

        std::cout
                << "19" << tm2->tm_year << '/' << tm2->tm_mon << '/' << tm2->tm_mday << '\t'
                << tm2->tm_hour << ':' << tm2->tm_min << ':' << tm2->tm_sec << '\t'
                << tm2->tm_zone << ':' << tm2->tm_gmtoff
                << std::endl;
        return 0;
}

gives:

-3600
0
1970/0/1        1:0:0   BST:3600

Notably, time zone BST and offset to UTC 3600. That I did not expect.