1: Introduce pointer

Variable name - > address - > Data

Function internal change, function external unchanged: (pass by value)

#include<stdio.h>

void swap(int a,int b)//Pass by address
{
	int temp=0;
	temp=a;
	a=b;
	b=temp;
}

int main()
{
	int a=3,b=4;
	printf("Before exchange a=%d,b=%d\n",a,b);//a=3,b=4
	swap(a,b);
	printf("After exchange a=%d,b=%d\n",a,b);//a=3,b=4
	return 0;
}

2: Pointer - pass by address

Pointer definition: pointer is the data type used to describe the address

The following a is a pointer variable of type int

#include<stdio.h>

void swap(int *a,int *b)//Pass by address
{    
	int temp=0;
	temp=*a;    //Address value
	*a=*b;
	*b=temp;
}

int main()
{
	int a=3,b=4;
	printf("Before exchange a=%d,b=%d\n",a,b);//a=3,b=4
	swap(&a,&b);                    //Address passed in
	printf("After exchange a=%d,b=%d\n",a,b);//a=4,b=3
	return 0;
}

3: Pointer variable: store the address of others

As follows: pointer variable p stores the address of variable a

#include<stdio.h>

void swap(int *a,int *b)//Pass by address
{  
	int temp=0;
	temp=*a;    //Address value
	*a=*b;
	*b=temp;
}

int main()
{	
	int a=1;
   //Pointer variable (store someone else's address)
	int *p=&a;//Definition and initialization of pointer variables
	printf("a Your address is:%p\n",&a);       //0019FF2C
	printf("Pointer variable p Your address is:%p\n",p);//0019FF2C (store others' addresses)
	return 0;
}

4: Pointer variable initialization

The pointer variable is initialized to NULL and 0 is cast to void*

#include<stdio.h>

int main()
{	
 //Pointer variable storage address
	int *p=NULL;//Definition and initialization of pointer variables
	printf("Pointer variable p Your address is:%p\n",p);//00000000
	return 0;
}

5: Pointer variables need to be initialized, otherwise the pointer will be null (dangerous operation)

#include<stdio.h>

int main()
{	
	int a=3,b=4;
    //The wild pointer program ended abnormally
	int *pa;   //Wild pointer
	int *p=NULL;//Pointer variable initialization NULL
	printf("Pointer variable pa Your address is:%p\n",pa);//CCCCCCCC
	return 0;
}

Therefore, be sure to initialize NULL

6: Two ways of pointer definition

1. Define and assign initial value

#include<stdio.h>

int main()
{	
    int a=3,b=4;
    int *p=NULL;//Definition 1 define and assign initial value
    p=&a;
    printf("Pointer variable p Your address is:%p\n",p);//0019FF2C
    printf("Pointer variable p The values are:%d\n",*p);//3 * value
	return 0;
}

2. Definition and assignment

#include<stdio.h>

int main()
{	
   int a=3,b=4;
   int *pb=&b;   //Definition 2 definition assignment
   printf("Pointer variable pb Your address is:%p\n",pb);//0019FF28
   printf("Pointer variable pb The values are:%d\n",*pb);//4
   return 0;
}

7: Pointers and pointer variables

The address of a variable is called the "pointer" of the change amount. The pointer is the address, which is used to describe the address

int * ptr / / ptr is a pointer variable of type int

Pointer variable: the address specially used to store another variable

Pointer variables are also variables. Pointer variables store other people's addresses, and * represents the value

Variables have addresses, so pointer variables also have addresses

#include<stdio.h>

int main()
{	
   int a=3,b=4;
   int *p=NULL;//Definition 1 define and assign initial value
   p=&a;
   printf("%p\n",&p);//0019FF24 pointer variable is a variable, and the variable has an address (the address of p)
   printf("%p\n",*&p);//0019FF2C pointer variable value also uses * to get the value is an address (the address of a). Pointer variable stores the address of others
	
   printf("Pointer variable p Your address is:%p\n",p);//0019FF2C pointer variable stores the address of others (the address of a)
   printf("Pointer variable p The values are:%d\n",*p);//The value of 3 * is the value of a
   return 0;
}

8: Pointer variable open space

1 byte 8 bits, 32-bit operating system 32-bit pointer variable open space is 4 bytes, which is independent of the base type and related to the stored content

#include<stdio.h>

int main()
{	
   int a=3,b=4;
   int *p=NULL;//Definition 1 define and assign initial value
   char *pt=NULL;
    p=&a;

	//Size of pointer variable open space
	printf("%d\n",sizeof(p));  //  4 int pointer
	printf("%d\n",sizeof(pt)); //  4 char pointer
	return 0;
}

9: void*

Use of void:

1. Function type

2. The void * type pointer represents the address of the object, but there is no information about the address of the object

void* k;//0 cast to void * is similar to NULL

Pointer benefits: no local, no extinction, used for function data transfer and parameter transfer. Passing by address, the function changes internally and externally.

&Get address -% p

*Value -% d

Only variables can get addresses, and values cannot get addresses. Cannot: & * P

*&Yes, you can get the value only after you have the address

*&A = = a first take the address of a and then the value of A. This formula is correct.

10: The pointer is an address and can be offset by the pointer

*p + +: first offset the address with p + +, then take the value of *, and the address changes to 28 - > 2C offset by 4 bits (int type pointer offset by 4 bits)

The char type pointer is offset by 1 bit, that is, the pointer offset is determined according to the basic data type.

(* p) + + is the first value and then increases by 1