On 04/05/2018 10:49 AM, Giuseppe Modugno wrote:
I need to use environment functionality in newlib to have a correct
result from localtime() with the western european timezone (I need TZ
environment variable). I also need to convert UTC struct tm to time_t
with mktime(), so I should delete TZ variable before calling mktime().
I know I can call setenv()/unsetenv(), but I would like to avoid
using dynamic allocation (that those functions use). So I'm thinking
to have two static const environments, such as:
static const char *const env_with_tz[] = {
"TZ=CET-1CEST,M3.5.0,M10.5.0/3", NULL };
static const char *const env_empty[] = { NULL };
and change the environment on-the-fly in the following way:
extern char **environ;
environ = env_with_tz; // or environ = env_empty;
Is it safe?
Of course I need to call tzset() before calling mktime()/localtime()
if the environment has changed.
Are you trying to avoid the dynamic allocation of set/unset at all, or
only when changing the TZ value? The reason for asking is that you
can avoid it in the latter case very easily. This is because setenv()
does not free or allocate if a new string fits in the space taken by
the prior value, and just overwrites the value (when the overwrite
flag is set). So you can set TZ=CET-1CEST,M3.5.0,M10.5.0/3, then
(rather than unsetting it), set TZ=GMT0. Then set it back to CET again.