cc compiler warning question.

[Gary S. Moss VLD/VMB <moss>]

In article <032D013E619F0000A3 at NRCNET.NRC.CA>, SERRER at NRCM3.NRC.CA (Martin Serrer) writes:
|> #include <stdio.h>
|> 
|> typedef struct { int a;        int b; } TINY;
|> typedef struct { TINY two;     int c; } SMALL;
|> typedef struct { SMALL *one[]; int f; } BIG;
|> BIG *zero;
|> 
|> main()
|> {       zero = (BIG *) malloc( (sizeof(BIG) + sizeof(SMALL) * 2) );
|>         zero->f = 1;
|>         zero->one[0].c = 2;
|>         printf("--- %i\n",zero->f);
|>         printf("--- %i\n",zero->one[0].c);
|> }
|> 
|> % cc t.c
|> ccom: Warning: t.c, line 18: illegal zero sized structure member: one
|>         } BIG;
|>       --^
You are declaring "one" as an array of unspecified, therefore zero size,
declare it as "SMALL **one;" instead.  In this context, there is a big
difference between the two declarations; the compiler knows how big a
"SMALL **" is. 


|> ccom: Warning: t.c, line 28: struct/union or struct/union pointer required
|>         zero->one[0].c = 2;
|>       ---------------^
You must use "->" rather than ".":
In the declaration "SMALL *one[];", one is an array of pointers to SMALL types.
Therefore, one[0] is a pointer and requires a "->" after it, not a ".".

|> ccom: Warning: t.c, line 29: struct/union or struct/union pointer required
|>       printf("--- %i\n",zero->one[0].c);
|>       -------------------------------^
Same thing as above.

You will also need to allocate storage for "one" separately from "zero":

if(	(zero = (BIG *) malloc( sizeof(BIG) )) == NULL
    ||	(zero->one = (SMALL *) malloc( sizeof(SMALL) * 2 )) == NULL )
	{ /* ALWAYS check success of malloc(3). */
	(void) fprintf( stderr, "No memory available!\n" );
	return 1;
	}

Of course, you *could* declare storage for zero like this:

BIG zero;

Rather than the first call to malloc, and leave your "."s as they are.

-Gary