[ILUG] C compilation error

[Niall O Broin]

OK - this tiny program

---------------------
#include <sys/time.h>

main() {
  struct tm *tp;

  tp = localtime();
  tp->tm_isdst;
}
---------------------

generates the following wrning and error

timeq.c: In function main':
timeq.c:8: warning: assignment makes pointer from integer without a cast
timeq.c:9: dereferencing pointer to incomplete type

when compiled on a SuSE 7.3 box with gcc 2.95.3 and glibc 2.2.4

It compiles with no warning or error on a SuSE 6.4 box with gcc 2.95.2 and
libc 2.1.3 (yes, libc, not glibc - seems like a strange libc version number
to me)

While I'm no C whizkid, nor am I C illiterate and I just don't understand
these errors. I have 
  
struct tm *tp;

and according to TFM

struct tm *localtime(const time_t *timep);

so why is my code generating the warning in line 8 ?

And what on earth is an "incomplete type" in line 9 ?


I've had a quick diff of time.h on both boxes and there are big differences
BUT the definition of a struct tm looks about the same AND the relevant bit
of TFM about localtime is the same on each box.


I can get rid of the warning by putting the cast in line 8 as

  tp = (struct tm *)localtime();
  
but why on earth should I have to when localtime IS already a pointer to a
tm struct ? And it still leaves the "incomplete type" error in line 9. 

I just tried on a couple of RH boxes I have access to - 6.2 bitches about
too few arguments to localtime but if I remove the localtime call it
compiles so it doesn't seem to regard the struct tm as an incomplete type.
That has egcs-2.91.66 and glibc-2.1.3. 

On a Verio box, which claims to be "Verio Enterprise Linux, based on Redhat
Linux 6 & 7", I get the same errors as on SuSE 7.3. That has gcc 2.95.3 and
glibc-2.2.4.


Can some C whizkid please put me out of my misery ?



Niall