Dynamic memory allocation (malloc calloc realloc free)

Memory is mainly divided into three parts , The stack area , Heap area , Static zone , The memory space created by the dynamic memory function is in the heap .

The stack area ： local variable , Function parameter

Heap area ： Dynamic memory allocation ,（malloc,calloc, realloc, free）

Static zone ： Global variables , Static variables

malloc function ：

malloc If the function opens space successfully , Then return the starting address of that space , If opening up space fails （ Possible causes ： There is too much room to open up ）, Then return to NULL, So check the returned pointer ,

When opening up space is successful , And after use , This space should be released as soon as possible （ Return this space to the operating system ）, application free（） Function frees up space , After release p It's a wild pointer , In order to avoid passing later p Illegal access to memory , Should put p Set as NULL

calloc function ：

calloc After opening up space , The space content will be initialized to 0

realloc function ：

 

 

realloc Functions can be divided into three cases ：

If realloc The first argument to the function is NULL, Then the function is equivalent to malloc

Here are some common errors in dynamic memory development ：

1. Dereference of null pointer ：

2. Cross border access to dynamic open space ：

 3. The release of non dynamic development space

4. Release a part of dynamic development memory

5. Multiple releases of the same dynamic memory

6. Dynamic memory forget to release （ Memory leak ）

Flexible array ：

1. At least one other member in front of the flexible array member in the structure

2.sizeof Return the size of this structure, excluding the memory of the flexible array

3. Structures that contain flexible array members use malloc() Function to dynamically allocate memory , And the allocated memory should be larger than the size of the structure , To fit the expected size of the flexible array .