Memory memory operation function

One 、malloc/calloc

name ：	malloc/calloc
function ：	Dynamic memory allocation function
The header file ：	#include <memory.h>
Function primitives ：	void *malloc(size_t size); void *calloc(size_t num,size_t size);
Parameters :	size     Size of allocated memory block num　　 Number of allocated memory blocks
Return value ：	The first address of the allocated memory block is returned successfully , Failure to return NULL.

        malloc and calloc Can allocate memory areas , but malloc Only one memory area can be requested at a time ,calloc You can apply for multiple memory areas at a time ． in addition calloc The allocated memory area will be initially converted into ０,malloc No initialization ．

#include <stdio.h>
#include <stdlib.h>
main()
{
    int *p=NULL;
    p=(int *)malloc(sizeof(int));
    if(p==NULL)
    {
        printf("malloc error\n");
        exit(1);
    }
    *p=3;
    printf("%d\n",*p);
    free(p);
}

Two 、free

name ：	free
function ：	Dynamic memory release function
The header file ：	#include <memory.h>
Function primitives ：	void free(void *ptr);
Parameters :	ptr    Use malloc or calloc Wait for the memory pointer returned by the memory allocation function
Return value ：	nothing

     free  Can be released by malloc or calloc Memory allocated by the memory allocation function ． When the program is large , You may have to dynamically allocate memory multiple times during , If not released in time , The program will take up a lot of memory ． it is to be noted that , If ptr The memory referred to has been released or the memory address is unknown , Then unexpected things may happen ． If the parameter is NULL, be free It won't work ．

3、 ... and 、memset

name ：	memset
function ：	Initialize the specified memory space
The header file ：	#include <memory.h>
Function primitives ：	void *memset(void *buffer,int c,int count);
Parameters :	buffer       Allocated memory c 　　　　  Initialize content count       Number of bytes initialized
Return value ：	Return to point buffer The pointer to

    memset hold buffer Before the memory area referred to count Bytes set to a character ASCLL value ． Generally used to give an array , String and other types of assignment ．

main()
{
    int *p=(int *)malloc(sizeof(int)*10); //  Distribute 10 individual Int
    if(p==NULL) exit(1);                  //  Error detection 
    memset(p,0,sizeof(int)*10);           //  Memory block is set 0
    free(p);                              //  Release 
｝

Four 、memcpy

name ：	memcpy
function ：	Copy memory space
The header file ：	#include <memory.h>
Function primitives ：	void *memcpy(void *dest,void *src,unsigned int count);
Parameters :	dest        Target memory area src　　    Original memory area count       Bytes to copy
Return value ：	Point to dest The pointer to

     memcpy Will be able to src The memory area referred to is copied count Byte to dest The memory area referred to ． If count Than src The number of bytes is large ,strcpy Can copy '\0' After that ． it is to be noted that dest and src Don't overlap ．memcpy Just copy memory space , Do not deal with spatial overlap ．

main()
{
    int *p1=malloc(sizeof(int)*10);
    int *p2=malloc(sizeof(int)*5);

    memset(p1,0,sizeof(int)*10);
    memcpy(p2,p1,sizeof(int)*5);

    free(p1);
    free(p2);
)

5、 ... and 、memmove

name ：	memmove
function ：	Copy （ Move ） Memory space
The header file ：	#include <memory.h>
Function primitives ：	void *memmove(void *dest,void *src,unsigned int count);
Parameters :	dest        Target memory area src　　　　 Original memory area count       Bytes to copy
Return value ：	Point to dest The pointer to

      Memmove And the function memcpy Functions function the same , But just copy memory space , Do not deal with spatial overlap ．Memmove Can deal with spatial overlap ． When dest and src When overlapping , Can still handle , but src Content changes ．

6、 ... and 、memcmp

name ：	memcmp
function ：	Compare the characters of two memory spaces
The header file ：	#include <memory.h>
Function primitives ：	int memcmp(void *buf1,void *buf2,unsigned int count);
Parameters :	buf1        Memory area buf2　　　  Memory area count       The number of characters to compare
Return value ：	See below

     Memcmp Will compare memory areas buf1 and buf2 Before count Bytes ．Memcmp Back basis ASCLL Code table sequence comparison ． When buf1<buf2 when , return <0; When buf1=buf2 when , return ０; When buf1>buf2 when , return ＞０．