[lug] localtime() returns pointer - free it?

[Tkil]

>>>>> "Michael" == Michael J Hammel <mjhammel at graphics-muse.org> writes: 

Michael> I noticed tonight that localtime() returns a pointer to a 
Michael> struct tm pointer.  Is the caller responsible for freeing the 
Michael> memory associated with that structure?   

it is usually a static extern that is returned, so (1) you don't need
to free it, (2) you don't *want* to free it, as that should cause your 
program to fall down and go boom, and (3) it's not thread-safe.

consider:

=============================================================================
#include <stdio.h>
#include <time.h>

int main()
{
  struct tm *a, *b;
  time_t t1;
  time_t t2;

  (void) time(&t1);
  t2 = t1+1;

  a = localtime(&t1);
  printf("a = 0x%p\n", a);
  
  b = localtime(&t2);
  printf("b = 0x%p\n", b);

  if (a == b)
  {
    printf("since they're the same, you don't need to `free' them.\n");
  }
  else
  {
    printf("since they're different, you DO need to `free' them.\n");
  }
}
=============================================================================

note that the two times are distinct, yet they return the same pointer.

Michael> Is the Linux behaviour (whether I need to free the space or 
Michael> not) consistant with other Unix platforms? 

so far as i know, this is a common response.  as i mentioned above,
this interface is not thread-safe; there might be alternatives that
*are* thread-safe, and those would probably have different interfaces
as well as probably adding the requirement that you provide the
structure to be filled in.

t.