Re: Are there some potential problems if I use a self-defined memory acquirement function instead of realloc(3) in the l_alloc function?

[Sean Conner <sean@...>]

It was thus said that the Great 孙世龙 sunshilong once stated:
> >What matters is what the language
> >standards say, and what they say is that realloc() is permitted to fail
> >when shrinking a block. (Some realloc implementations never fail in that
> >case, but many in common use do.)
> Could you please please give me some references or documents for me to
> go through?
> What about malloc(3) provided by the stand C library?

  Nothing better than the C Standard document itself.  They're pretty easy
to find on the Internet (I found the C89, C99 and C11 standards).

  But the descriptions are small enough to quote here.  For malloc():

	#include <stdlib.h>
	void *malloc(size_t size);

	The malloc function allocates spae for an object whose size is
	speificied by size and whose value in indeterminate.

	The malloc function returns either a null pointer or a pointer to
	the allocated space.

(wording is the same for C89, C99 and C11).  For free():

	#include <stdlib.h>
	void free(void *ptr);

	The free function causes the space pointed to by ptr to be
	deallocated, that is, made available for further allocation.  If ptr
	is a null pointer, no action occurs.  Otherwise, if the argument
	does not match a pointer earlier returned by the calloc, malloc, or
	realloc funciton, or if space as been deallocated by a call to free
	or realloc, the behavior is undefined.

	The free function returns no value.

(wording is the same for C89, C99 and C11).  And finally realloc()---the
wording changed between C89 and C99/C11, so first, C89:

	#include <stdlib.h>
	void *realloc(void *ptr,size_t size);

	The realloc function changes the size of the object pointed to by
	ptr to the size specified by size.  The contents of the object shall
	be unchanged up to the lesser of the new and old sizes.  If the new
	size is larger, the value of the newly allocated portion of the
	object is indeterminate.  If ptr is a null pointer, the realloc
	function behaves like the malloc function for the specified size. 
	Otherwise, if ptr does not match a pointer earlier return by calloc,
	malloc, or realloc function, or if the space has been deallocated by
	a call to the free or realloc function, the behavior is undefined. 
	If the space cannot be allocated, the object pointed to by ptr is
	unchanged.  If size is zero and ptr is not a null pointer, the
	object it points to is freed.

	The realloc function returns either a null pointer or a pointer to
	the possibly moved allocated space.

and finally C99/C11 (wording is the same for both):

	#include <stdlib.h>
	void *realloc(void *ptr,size_t size);

	The realloc function deallocates the old object pointed to by ptr
	and returns a pointer to a new object that has the size specified by
	size.  The contents of the new object shall be the same as that of
	the old object prior to deallocation, up to the lesser of the new
	and old sizes.  Any bytes in the new object beyond the size of the
	old object have indeterminate values.

	If ptr is a null pointer, the realloc function behhaves like the
	malloc function for the specfified size.  Otherwise, if ptr does not
	match a pointer earlier returned by the calloc, malloc, or realloc
	function, or if the space has deallocated by a call to the free or
	realloc function, the behavior is undefined.  If memory for the new
	object cannot be allocated, the old object is not deallocated and
	its value is unchanged.

	The realloc function returns a pointer to the new object (which may
	have the same value as a pointer to the old object), or a null
	pointer if the new object could not be allocated.

  -spc (any typos are mine, it's best to refer to the actual documents)