Critique of realloc() wrapper

Seeking code correctness and best practices.

I would like to re-allocate various amounts of memory (0 or more) such that on systems that may return NULL for an allocation of 0 does not falsely imply a memory allocation error.

Given:

• void * (with a valid value or NULL already)

• size_t (new desired size)

Receive:

• void * (new pointer)

• int (failure status)

#include 
#include 

int ReallocAndTest(char **Buf, size_t NewSize) {
  assert(Buf);
  char *NewBuf = realloc(*Buf, NewSize);
  if ((NewBuf == NULL) && (NewSize > 0)) {
    return 1;  // return failure
  }
  *Buf = NewBuf;
  return 0;
}

I came across the below references, which imply a realloc() return of NULL is not always a failure. The lone special case occurs with size is 0. The return value may or may not be NULL.


C11dr 7.22.3.5 The realloc function 4 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.


C11dr §J.1 Unspecified behavior. — The amount of storage allocated by
a successful call to the calloc, malloc, or realloc function when 0
bytes was requested (7.22.3).


C11dr §J.3.12 Implementation-defined behavior. Whether the calloc,
malloc, and realloc functions return a null pointer or a pointer to an
allocated object when the size requested is zero (7.22.3).

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Discusses how a memory allocation of 0 is useful.

Answer: when a routine has a malloc(size), testing for size != 0 is not needed.

what's the point in malloc(0)?

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Asks if realloc(ptr), 0) is the same as free(ptr).

Answer: Not necessarily.

What happens if I re-alloc and the new size is 0. Is this equivalent with a free?

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Allocation wrapper set.

Answer: Does not address realloc(ptr, 0).

Are these memory-allocation wrapper functions kosher with all C compilers?

[Answer]

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Use void rather than char .

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With a 0 size, avo

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Standard naming convention in C is usually lower_case_with_underscore.

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You should be using void rather than char

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I would consider making the return value deterministic when the new size is 0 by always returning NULL rather than the implementation defined behaviour (which could technically be a pointer which is not NULL but still not allowed to be dereferenced). free guarantees by spec that free(NULL) is legal.

StackExchange Code Review Q#36662, answer score: 6