realloc in C?
In C, the most fundamental dynamic memory functions are
free, provided in
malloc (“memory allocate”) function allocates a block of memory on the heap; the
free function frees it again. Their signatures are:
void* malloc(size_t size); void free(void* ptr);
But there are a couple more:
void* calloc(size_t how_many, size_t num_elements); void* realloc(void* original, size_t new_size);
calloc (“clear alloc”) function behaves like
malloc, with two differences:
- Instead of a raw
size_t, it takes two
size_ts: the first representing the number of objects in an array, and the second representing the size of each object in the array. It then allocates space for such an array.
- It zeroes the allocated memory.
realloc (“reallocate”) function takes a pointer to an allocated block, and attempts to expand/contract that block to the new size. If it cannot, it allocates the requested size elsewhere, and copies the old version to it. If the new size is larger than the old, then the trailing memory is uninitialized.