Malloc C language

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the standard library provides analogous functions called malloc and free that have no such restrictions;

 

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the functions malloc and calloc obtain blocks of memory dynamically.

void *malloc( size_t n)

returns a pointer to n bytes of uninitialized storage, or NULL if the request can not be satisfied.

void *calloc( size_t n, size_t size)

returns a pointer to enough space for an array of n objects of the specified size, or NULL if the request cannot be satisfied. The storage is intialized to zero.

The pointer returned by malloc or calloc has the proper alignment for the object in question, but it must be cast into the appropriate type, as in

int *ip;
ip = ( int * ) calloc ( n ,sizeof( int ) );

free (p) frees the space pointed to by p, where p was originally obtained by a call to malloc or calloc. There are no restrictions on the order in which space is freed, but it is a ghastly error to free something not obtained by
calling calloc or malloc.

 

It means c Standard library files stdlib.h It has malloc function

Its function definition is like this ：

void *malloc( size_t size)

From this we can see , The return value of this function is null pointer type . This pointer points to the memory space allocated according to our needs , If the request fails （ That is, if the space allocation fails ） return NULL.

The following example says

str = ( char * ) malloc( 15 );

  Distribution 15byte Space , then malloc The function returns a pointer to this 15byte Spatial void*, Null pointer type . Then cast the type to char * type

Two pictures are from https://www.tutorialspoint.com/c_standard_library/c_function_malloc.htm