The generation and release of heap space in C language

Allocation and release of heap space
  # include < Stdlib. H >
  Malloc, calloc, realloc, free
  The malloc
  Void * malloc (size_t size);
  Function: allocate size bytes of contiguous space in the heap
  Parameter: size_ number of bytes
  Return value: returns the first address of the allocated space on success and NULL on failure
 
  free
  Void free (void * PTR);
  Function: free space allocated by malloc, calloc, realloc
  Parameter: the first address of the ptr_ space
  Return value: none
  Note:
  1. Each space can only be released once
  2. PTR must be the first address of the allocated space

  calloc
  Void *calloc(size_t nmemb, size_t size);
  Function: allocate contiguous space in the heap with nmemb block size of size bytes
  Parameter: nmemb_ data block size size_ each size
  Return value: returns the first address of the allocated space on success and NULL on failure
  Note: Calloc sets the space content to zero, whereas malloc does not

  realloc
  Void *realloc(void * PTR, size_t size);
  Function: in malloc, calloc, realloc allocated PTR start space, reassign to size byte size
  Parameters: ptr_malloc, calloc, realloc allocate space first address size_ total size
  Return value: successfully returns the first address of the allocated space and fails to return NULL
 
  Note:
  1. If the size is less than the original space size, it will not work
  2. The newly added space will not set 0
  3. If PTR is NULL, it is equivalent to malloc(size).
  4. If PTR is not NULL and size == 0, it is equivalent to free(PTR).
  5. PTR does not need to be released. If the allocation is successful, only the first address of the redistribution space is released