Functions for memory allocation and deallocation

Comparison of multiple-alloc: Alloc: The only application for memory on the stack, no release; malloc: application memory on the heap, most commonly used; calloc:malloc+ initialized to 0; ReAlloc: Expands the memory area that was originally requested, the size of the parameter size is the expansion Size, so this function requires that size must be larger than the size of the PTR memory

The difference between malloc and calloc is the difference between 1 blocks and n blocks and initialization

The ReAlloc invocation form is (type *) realloc (*ptr,size): Increases the PTR memory size to size.

Functions for memory allocation and deallocation