zero size malloc [duplicate]

Solution 1:

The behaviour is implementation defined, you will receive either a NULL pointer or an address. Calling free for the received pointer should however not cause a problem since:

• free(NULL) is ok, no operation is done
• free(address) is ok, if address was received from malloc (or others like calloc etc.)

Solution 2:

It's allowed to return NULL, and it's allowed to return a non-NULL pointer you can't dereference. Both ways are sanctioned by the standard (7.20.3):

If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.

Solution 3:

Sorry for the trouble, I should have read the man pages :

malloc() allocates size bytes and returns a pointer to the allocated memory. The memory is not cleared. If size is 0, then malloc() returns either NULL, or a unique pointer value that can later be successfully passed to free().

free() frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc(), calloc() or realloc(). Otherwise, or if free(ptr) has already been called before, undefined behavior occurs. If ptr is NULL, no operation is performed.

It seems it is true at least for the gnu libc

Solution 4:

According to the c standard

7.20.3 If the size of the space requested is zero, the behavior is implementation defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.