calloc malloc realloc

calloc

void * calloc ( size_t num, size_t size );

Allocate space for array in memory
Allocates a block of memory for an array of num elements, each of them size bytes long, and initializes all its bits to zero.

The effective result is the allocation of an zero-initialized memory block of (num * size) bytes.

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malloc

void * malloc ( size_t size );

Allocate memory block
Allocates a block of size bytes of memory, returning a pointer to the beginning of the block.

The content of the newly allocated block of memory is not initialized, remaining with indeterminate values.


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realloc

void * realloc ( void * ptr, size_t size );

Reallocate memory block
The size of the memory block pointed to by the ptr parameter is changed to the size bytes, expanding or reducing the amount of memory available in the block.

The function may move the memory block to a new location, in which case the new location is returned. The content of the memory block is preserved up to the lesser of the new and old sizes, even if the block is moved. If the new size is larger, the value of the newly allocated portion is indeterminate.

In case that ptr is NULL, the function behaves exactly as malloc, assigning a new block of size bytes and returning a pointer to the beginning of it.

In case that the size is 0, the memory previously allocated in ptr is deallocated as if a call to free was made, and a NULL pointer is returned.


Parameters

ptr
    Pointer to a memory block previously allocated with malloc, calloc or realloc to be reallocated.
    If this is NULL, a new block is allocated and a pointer to it is returned by the function.
size
    New size for the memory block, in bytes.
    If it is 0 and ptr points to an existing block of memory, the memory block pointed by ptr is deallocated and a NULL pointer is returned.