Go4Expert - find timezone using C

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find timezone using C

how to know the timezone using C ...

i want something which will work both on Linux and Windows...

for example in case of India...i wish to know using the program that the timezone is GMT+ 5:30

i found a variable called _timezone which works in case of Windows but not on Linux.

Re: find timezone using C

http://www.hmug.org/man/3/strftime.php
http://www.hmug.org/man/3/ctime.php
gmtime(), localtime(), strftime() would seem to be functions worth a look.

Re: find timezone using C

i have tried all the above functions...but what i need is to print the current time in the undermentioned format:
Tue Jan 08 2008 22:25:22 GMT+0530 (India Standard Time)

i am able to print everything except GMT+530 using the function strftime...
so i am looking for some variable or function which can tell me the current timezone..
and i have to find the solution only within the ANSI/C89 boundaries..the functions like localtime must be using something to chge the time from UTC to localtime..

Re: find timezone using C

So what does this produce for you?

Code:

#include <stdio.h>

#include <time.h>



int main() {

    time_t  now = time(NULL);

    struct tm tnow = *gmtime(&now);

    char    buff[100];

    strftime( buff, sizeof buff, "%a %b %d %Y %T %Z%z", &tnow );

    printf( ">>%s<<\n", buff );

    return 0;

}

Re: find timezone using C

This is the output i get..instead of the time difference in number...i get India Standard Time twice...!!

>>Wed Jan 09 2008 India Standard TimeIndia Standard Time<<

as I stated earlier ..i need GMT+0530..

for the time being what i am doing is ..subtracting the value of localtime and gmtime..
hence i get the time difference in seconds..(which comes out to be 19800 seconds in case of India) ...so i calculate number of hours from it and concatenate it to my output string...

but i still need a way out of calculating the time difference...

Re: find timezone using C

this is something what i have tried and is now giving the right output...
still looking for an easy way out :D :)

Code:

#include <stdio.h>

#include <time.h>

#include <string.h>

#include <stdarg.h>

#include <stdlib.h>

#include <math.h>



char tzarray[13][3] = {"00", "01", "02", "03", "04", "05", "06", \

"07", "08", "09", "10", "11", "12"};

char tzmin[][3] = {"00", "30"};



int main(void) {

    long dtime = 0;

    short diffhour = 0;

        char diffmin[3] = {"00"};

    char *strtm, *strzone;

    time_t tm1, tm2;

        struct tm *t1, *t2;

    strtm = malloc(120 * sizeof(char));

    strzone = malloc(50 * sizeof(char));

    tm1 = time(NULL);

    t2 = gmtime(&tm1);

    tm2 = mktime(t2);

        t1 = localtime(&tm1);

    dtime = (long)(tm1 - tm2);

/* Print local time as a string */

    strftime(strtm, 100, "%a %b %d %Y %H:%M:%S GMT", t1);

    if (dtime >= 0 )    

                strcat(strtm, "+");

    else 

                strcat(strtm, "-");

        strcat(strtm, tzarray[(short)(abs(dtime) / 3600)]);

    if (1800 == (short)(abs(dtime) % 3600))

                strcat(strtm, tzmin[1]);

        else

                strcat(strtm, tzmin[0]);

    strftime(strzone, 50, " (%Z)", t1);

    strcat(strtm, strzone);

    printf("%s\n\n\n", strtm);

    return 0;

}

Re: find timezone using C

ignore the indentation in the last post...
it messed while copying the code from Visual Studio editor to explorer.. :)