Thread: Realloc Double Free

Originally Posted by mingerso

This was mentioned earlier but heres an example of realloc and not destroying your previous pointer ( so you can avoid bad free()'s and memory leaks ):

Code:

char * add_space(char ** str)
{
	int len = strlen(*str);
	char * tmp = (char *)realloc(*str, sizeof(char)*len+2);
	if(tmp)
	{
                /* allocation was ok so we have our new address to point to */
		*str = tmp;
	} else {
		/* out of memory, so do something... or not */
		free(*str);
	}

	/* now you can error check the function on NULL or not */
	return tmp;	
}

Hope that helps.

There's "*str=NULL;" missing after "free(*str);" - in case free() will be used, and return value of function ignored...

That is the typical method but depends on what you're doing. It is not required and I see your point, but if you're going to be using pointer allocations this way you might want to make a wrapper for free() that sets it for you:

Code:

void * safe_free(void * ptr)
{
	if(ptr)
		free(ptr);
	return NULL;
}

var = safe_free(var);

Originally Posted by matsp

I would prefer something like this:

Code:

void safe_free(void **ptr)
{ 
   if (ptr)   // Check for stupid programmer errors
   {   
      free(*ptr);
      *ptr = NULL;
   }
}

// And to complete it... 
#define free(x) safe_free(&x)

--
Mats

My style (preference?) exactly

Yes all very good points of preference... and back to what was being said:

"... so do something... or not"