Can malloc be NULL?
Yes. Malloc will return NULL when the kernel/system lib are certain that no memory can be allocated. The reason you typically don’t see this on modern machines is that Malloc doesn’t really allocate memory, but rather it requests some “virtual address space” be reserved for your program so you might write in it.
What happens when malloc returns NULL?
If the malloc function is unable to allocate the memory buffer, it returns NULL. Any normal program should check the pointers which the malloc function returns and properly handle the situation when the memory allocation failed.
Does malloc 0 return NULL?
[EDITED: it can sometimes allocate memory, see my next answer] The return value of malloc (0) is implementation specific: it can return NULL or a valid pointer (some unique value) as in your case but memory is not allocated!!!
Why is malloc void?
malloc returns a void pointer to the allocated space, or NULL if there is insufficient memory available. To return a pointer to a type other than void , use a type cast on the return value.
What does malloc return if failed?
According to the Single Unix Specification, malloc will return NULL and set errno when it fails.
How do I know if malloc failed?
We can also use the Malloc function to check for errors about memory allocation. When a malloc method finds itself unable to allocate memory, it usually returns NULL. You can also through an error message if the allocation got failed upon managing the pointers.
Can you realloc NULL?
If size is 0, either a null pointer or a unique pointer that can be successfully passed to free() is returned. If there is not enough available memory, realloc() returns a null pointer and sets errno to [ENOMEM].
What is void * malloc?
void* malloc( size_t size ); Allocates size bytes of uninitialized storage. If allocation succeeds, returns a pointer that is suitably aligned for any object type with fundamental alignment. If size is zero, the behavior of malloc is implementation-defined.
Why the return value of dynamic memory allocation functions is void *?
This is because these methods are allocating memory without any specific type. If malloc returned int* and you allocate only 1 byte, you would never be able to dereference it safely without casting.
How do I know if malloc is successful?
With MemSize == 0 , receiving a malloc() return value of NULL is compliant behavior and not an allocation failure. Changing to if(NULL == AllocMem && MemSize != 0) fixes that.
Is it OK to free null?
It is safe to free a null pointer. The C Standard specifies that free(NULL) has no effect: 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.
What happens when malloc (0) returns null?
In other words, malloc (0) may return a NULL -pointer or a valid pointer to zero allocated bytes. Just check the manual page of malloc. On success, a pointer to the memory block allocated by the function.
What does malloc do in C++?
The malloc function allocates a memory block of at least size bytes. The block may be larger than * size`* bytes because of the space that’s required for alignment and maintenance information. malloc sets errno to ENOMEM if a memory allocation fails or if the amount of memory requested exceeds _HEAP_MAXREQ.
How many bytes does malloc allocate?
The malloc function allocates a memory block of at least size bytes. The block may be larger than size bytes because of the space that’s required for alignment and maintenance information.
Why does malloc set errno to enomem when a block is larger?
The block may be larger than size bytes because of the space that’s required for alignment and maintenance information. malloc sets errno to ENOMEM if a memory allocation fails or if the amount of memory requested exceeds _HEAP_MAXREQ.