更改时区不更改时区的日期格式

Question

In the below code I try to display the pdt and gmt format of epoch time value "1411636989", but it changes only time zone not the date, following is the sample output.

int main()
{
    time_t my_time = 1411636989;

    if (putenv("TZ=PDT"))
        printf("Current time zone = %s###########\n", getenv("TZ"));
    else {
        printf("Time zone = %s###########\n", getenv("TZ"));
        printf("PDT 1411636989 = %s$$$$$$$$$$$$$$$$$$\n", asctime(localtime(&my_time)));
    }

    if (putenv("TZ=GMT"))
        printf("putenv failed errno = %d##########\n",errno);
    else {
        printf("New time zone = %s###########\n", getenv("TZ"));
        printf("GMT 1411636989 = %s$$$$$$$$$$$$$$$$$$\n", asctime(localtime(&my_time)));
    }

    return 0;
}

Sample O/P:
Time zone = PDT###########
PDT 1411636989 = Thu Sep 25 09:23:09 2014
$$$$$$$$$$$$$$$$$$
New time zone = GMT###########
GMT 1411636989 = Thu Sep 25 09:23:09 2014
$$$$$$$$$$$$$$$$$$

Answer 1

You'll have to use one of the timezone matching a file name below the /usr/share/zoneinfo/ directory. A TZ of PDT isn't going to be recognized. The system will fall back to GMT if your TZ variable isn't valid.

Set it to "US/Pacific".

putenv("TZ=US/Pacific")

Answer 2

Since time_t is usually represented in seconds use normal arithmetic to add value to my_time .

Before if(putenv("TZ" = "GMT")) add this line to increase the time to GMT:

my_time += (7 * 60 * 60);