strptime error when setting a different TimeZone with export TZ=UTC

Brian Dessent
Fri Jun 24 19:42:00 GMT 2005

Luca Wullschleger wrote:

> Hi everybody. I have a very specific problem and I'm looking for someone
> giving me a solution.

I'm afriad this is operator error on your part.

>         struct tm try;

Here 'try' starts out as a regular automatic variable, with all of its
fields set to arbitrary (undefined) values.

>         if ((char *)strptime(date,"%d/%b/%Y:%T",&try) == NULL) {

Here you call strptime() to fill in the values of 'try', however the
strptime function has the semantics that it will only fill in the
members of struct tm that it is asked to parse.  This means that after
the call, some of the members still have undefined values. 
Specifically, the members tm_wday, tm_yday, and tm_isdst will contain

>         ts2 = mktime(&try) - atoi(timezone)*3600;

And here you pass this value of 'try' that still has uninitialized
values to mktime(), the result of which will be undefined as well.  I
think you were just lucky that it worked in the case where TZ was not
set, but in general once you encounter the situation where you pass
uninitialized data to a function, all bets are off because your program
is invalid C.

If you change the line above to "struct tm try = { 0 };" or otherwise
initialize it somehow, then I think you will get the desired


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