Re: when can realloc fail?

<banansol@xxxxxxxxxxxx> wrote in message
Hi,
I just want to get this right.
A call to realloc() will return NULL on error and the original memory
is left untouched,
both when requesting a larger or a smaller size that the original,
right?
But a call to realloc() with size set to zero is equivalent to free(),
with returns void.
Does that mean that a call to realloc() can fail when shinking memory
except when
shrinking it to zero in which case it will always succeed?

It is a bit of a grey area.

Normally you want the construct

temp = realloc(ptr, newsize);
if(temp == 0)
{
fprintf(stderr, "Oh no, out of memory\n");
free(ptr);
return -1;
}
ptr = temp;
..... /* do something useful */
free(ptr);
return 0;

it is quite a lot of code simply to perform memory management. However if newsize is zero you've entered a grey area. temp could be zero or a valid pointer assuming that the function doesn't fail. If we say that realloc() must return a pointer to a block of no memory then you've also got the potential for a fail. Then it is not unlikely that your code, knowing that newsize is zero and it is working on an empty data set, will forget to call free() on ptr.
--
Free games and programming goodies.
http://www.personal.leeds.ac.uk/~bgy1mm


.

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