Thread: unions and structs

I can't understand why I get the following errors.
Here is my code:

Code:

union header{ /* block header         [LINE 11] */
	struct{
		unsigned int size; /* size of this block */
		int prev_check = 0;
		union header *ptr; /* next block if on free list */

	} s;
	Align x; /* force alignment of blocks */
};

typedef union header Header; /*[LINE 20]*/

These are the errors that I get:

Code:

mymalloc.c:14: warning: no semicolon at end of struct or union
mymalloc.c:14: error: syntax error before '=' token
mymalloc.c:14: warning: no semicolon at end of struct or union
mymalloc.c:17: error: syntax error before '}' token
mymalloc.c:17: warning: data definition has no type or storage class
mymalloc.c:19: error: syntax error before '}' token

I am getting this error just by declaring a variable: int prev_check. I wont get these errors when I remove that line. Please advise.

You can't initialize variables in a union declaration. In other words: no = 0 allowed.

Just took a baton and hit my head.

What should I be searching for if I get the following:

Code:

warning: implicit declaration of function `morecore'
warning: assignment makes pointer from integer without a cast
At top level:
error: conflicting types for 'morecore'
error: previous implicit declaration of 'morecore' was here

This is the snippet of code

Code:

if (p == freeptr) /*p & freeptr are pointers */
     if ((p = morecore(nunits)) == NULL)  /*morecore returns a pointer */
	 return NULL; /* none left */

You might be missing a header file -- apparently there was no declaration of morecore in scope at the first part. (The second one is probably your definition of morecore, with the proper types, which don't match the implicit int.)

Well you were right, I forgot to add it in the header file. But after adding it (same function statement) I get 2 error for previous declaration and conflicting type errors for the same line in the header file as well as c file.

Code:

mymalloc.c:69: error: conflicting types for 'morecore'
mymalloc.h:6: error: previous declaration of 'morecore' was here
mymalloc.c:69: error: conflicting types for 'morecore'
mymalloc.h:6: error: previous declaration of 'morecore' was here

So now there's a conflict between your prototype in your header file and reality (as expressed in your c file). Just copy the top line of your function, change the curly-brace to a semicolon, and make that your prototype -- it will save heartache later on.

As I had said in my earlier mail, I had done so. If you look at the earlier errors mentioned in this forum. Im thinking does it have anything to do with the warning : assignment makes pointer from integer without a cast.

Originally Posted by Ron

As I had said in my earlier mail, I had done so. If you look at the earlier errors mentioned in this forum. Im thinking does it have anything to do with the warning : assignment makes pointer from integer without a cast.

You just said you aren't getting that warning any more.

But no, what I mean is that your prototype might be something like

Code:

int * morecore(int something);

but your code actually has

Code:

int morecore(int something) {
  /* stuff */
}

thank you 'tabstop', but that is what I had done. Still the errors.

Originally Posted by Ron

thank you 'tabstop', but that is what I had done. Still the errors.

What I'm trying to get you to do is show us line 69 of mymalloc.c and line 6 of mymalloc.h, which are the two lines mentioned in the last error message you posted.

Code:

line 6
static Header *morecore(unsigned long nunits);

line 69
static Header *morecore(unsigned long nunits)
{



}

Well, I've tried to recreate the error, but can't. (I had at first thought that a forward declaration of Header might cause problems, but that seemed to work just fine.) The only thing I can think of at this point is that Header might mean different things at different times? That's the best guess I can make right now.