LinuxQuestions.org - problem with time zone change in c++

Hi all,

I have write a little function which can get the time zone value from a time zone name.
Here is the code:

Code:

  string getTimeZone(const string& zoneName)

    {

        struct tm *t1, *t2;

        time_t tm1, tm2;



        // LOCAL TIME (Europe/Zurich)

        tm1 = time(NULL);

        string tz = "TZ=";

        

        // set the new TZ value (TZ=zoneName)

        putenv((char *)(tz+zoneName).c_str());  

        

        // check

        envTz = getenv("TZ");

        if (envTz != NULL)

                cout << "TZ2 = "<<envTz<<endl; 

        

        long dtime = 0;



        // GMT time

        t2 = gmtime(&tm1);

        tm2 = mktime(t2);

        t1 = localtime(&tm1);

        dtime = (long)(tm1 - tm2);

        short min = (short)(abs(dtime) %3600/60);



        ostringstream os;

        os <<boost::format("%|0+3d|")%(short)(dtime/3600)<<":"<< boost::format("%|02|")%min;

        

        return os.str();

        

    }



int main(int        argc,char *        argv[])

{

    cout << "America/Denver : "<<getTimeZone("America/Denver")<<endl;

    cout << "America/Denver : "<<getTimeZone("America/Denver")<<endl;

    cout << "Indian/Comoro : " <<getTimeZone("Indian/Comoro")<<endl;

    cout << "Asia/Iran : " << getTimeZone("Asia/Iran")<<endl;;

    cout << "Canada/Atlantic : "<<getTimeZone("Canada/Atlantic")<<endl;

    

    return 0;



}

Result :

Code:

TZ2 = America/Denver

America/Denver : +01:00    <---- Problem

TZ2 = America/Denver

America/Denver : -07:00    <---- Same is correct !!!??!!

TZ2 = Indian/Comoro

Indian/Comoro : +03:00

TZ2 = Asia/Iran

Asia/Iran : +00:00

TZ2 = Canada/Atlantic

Canada/Atlantic : -04:00

As you can see, the first result is bad !

Any idea ?