Pointer operation - C language

First , Let's start with a simple piece of code

#include<stdio.h>
int main（void）
{
  char  ac[]={0,1,2,3,4,5,6,7,8,9};
  char  *p = ac;
  printf("p =%p\n",p);
  printf("p+1 =%p\n",p+1);
  int ai[]={0,1,2,3,4,5,6,7,8,9};
  int *q= ai;
  printf("q =%p\n",q);
  printf("q+1 =%p\n",q+1);
  return 0;
}

After running

p           =0*bffbad5a

p+1=p  =0*bffbad5b

q         =0*bffbad2c

q+1     =0*bffbad30

You can see p+1 Compared with p Address to add 1    and q+1 But added 4 （2c=44   30=48）

Why? ？

because sizeof（char）=1    sizeof（int）=4

So when we add one hour to a pointer Not adding one to the address   But add sizeof（ type ） Value

#include<stdio.h>
int main（void）
{
  char  ac[]={0,1,2,3,4,5,6,7,8,9};
  char  *p = ac;
  printf("p =%p\n",p);
  printf("p+1 =%p\n",p+1);
  printf("*(p+1)=%d\n",*(p+1));
  int ai[]={0,1,2,3,4,5,6,7,8,9};
  int *q= ai;
  printf("q =%p\n",q);
  printf("q+1 =%p\n",q+1);
  printf("*(q+1)=%d\n",*(q+1));
  return 0;
}

After running *(p+1）=1           *(q+1)=1

It indicates that the array where the two pointers are located has moved an element behind    Instead of adding one to the address

therefore   Add... To a pointer 1 Indicates that you want the pointer to point to the next variable

int a[10];

int *p=a;

*(p+1)--->a[1]

*p++

Take out p The data referred to comes from , When you're done, drop in p Move to the next position
* High priority though , But no ++ High is often used for continuous space operations of array classes
In some CPU On , This can be translated directly into an assembly instruction
 

  Pointer calculation ：

      1  Add or subtract an integer to the pointer

      2  Increasing decreasing

      3  Subtraction of two pointers

      4  Pointer cannot multiply or divide

The two hands subtract

If the above code   *p=&ac[0]   *p1=&ac[5]   Make p1-p     obtain p1-p=5

The difference obtained is not the difference of the address It is   Address difference /sizeof   The result is that there are several such elements between two pointers

Pointer comparison

<,<=,==,>,>=,!=       Can compare the addresses of pointers in memory
The addresses of the cells in the array must be linearly increasing

Two different types of pointers cannot be operated

Pointer type conversion

void* The pointer indicating that you don't know what to point to is calculated with char* identical （ But it's not connected ) Pointers can also convert types
int*p = &i; void*q = (void*)p;
It doesn't change p Type of variable referred to , But let later generations pass through with different eyes p Look at the variables it refers to

I don't think you are anymore int La , I think you are void!