C language memory function

c Language has functions to operate memory , Respectively ：malloc,realloc,calloc,free.

Why should there be memory functions ？

In terms of personal feelings , When developing an address book , Everyone's address book is different , This makes it difficult to determine how much memory you need to create for the structure array . If you do not use memory functions , Then simply and roughly set the structure array to be very large , It's hard not to waste memory .

malloc：

void* malloc (size_t size);

1.malloc The function is responsible for applying for a continuous space from memory , If the application is successful , Then return the address of the space , If the application fails , Then return to NULL.

2. Because I don't know what type you want , therefore malloc The return is void* The pointer to .

3. If malloc Transmitted size_t Parameter is 0, What value is returned ,c The language standard is not defined , Depends on the compiler .

calloc：

void* calloc (size_t num, size_t size);

1.calloc and malloc equally , It is also to apply for a continuous memory space , Successful application , The return address , Failure , return NULL.

2.calloc It's an application num individual size Size space .

3.calloc Function after successful application , Each byte of this space will be initialized to 0.

realloc：

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

1.realloc Used to adjust the dynamic memory size . If the rear memory is enough to accommodate the new memory size , be realloc Will be in ptr After adding , Make the memory become size size . But if it's not enough ,realloc Will find a piece of memory again , The memory address will change .

2.realloc Function if it fails , Returns the NULL, If successful, return the address . Because I don't know whether it will succeed , So it's using realloc When , Can't directly realloc The return value of is assigned to ptr, To create an intermediate pointer , If the middle pointer is not NULL, Then assign the middle pointer to ptr.

free：

void free (void* ptr);

1.free Function is used to reclaim dynamic memory .

2.c Language standards are not defined , When to ptr What should I do when the address of is not the address opened by dynamic memory , It depends on the compiler .

3. If ptr by NULL, be free Functions do not produce behavior .