Catalog

Advance of pointer

Preface

1. Character pointer

2. Array pointer

3. Pointer array

4. Array parameter passing and pointer parameter passing

5. A function pointer

6. Function pointer array

7. A pointer to an array of function pointers

8. Callback function

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Advance of pointer

Preface

In the simple pointer above, we introduced some common uses of simple pointers

link ： Simple pointer

This issue , Let's learn the pointer usage of the advanced version .

1. Character pointer

  among *p It doesn't point to “abcdef” Put the pointer p in , Instead, the address of the first character is placed in the pointer p in . This is a mistake that many people often make .

Because of this nature , When printing a single character , The pointer needs to be dereferenced , While using %s When printing the whole string , Just pass the first element address , The pointer just points to the address of the first element .

Once an interview example ：

  The answer is ：......not same        .......same

reason ： The first two character arrays , Is to put the characters in str1、str2 in , The two addresses are different . So they are different . And the pointer str3、 The pointer str4 It refers to the string stored in the same memory , So they are the same .

 

2. Array pointer

seeing the name of a thing one thinks of its function , This is a pointer , And it's a pointer to an array .

So what kind of form is he ？ We know

int* arr[10];

because [ ] The priority of is higher than * You have to be tall , therefore , Array names are precedence and [ ] The combination of , This is the pointer array .

therefore , We should make sure that * And array name first , Form the following ：

int (*arr)[10];

& The difference between array name and array name

We know that the array name represents the address of the first element of the array , that & What does the array name represent ？ Let's look at this code ：

#include <stdio.h>
int main()
{
    int arr[10] = {0};
    printf("%p\n", arr);
    printf("%p\n", &arr);
    return 0;
}

The operation results are as follows ：

You can see that the result is the same , But is it really the same ？

#include <stdio.h>
int main()
{
 int arr[10] = { 0 };
 printf("arr = %p\n", arr);
 printf("&arr= %p\n", &arr);
 printf("arr+1 = %p\n", arr+1);
 printf("&arr+1= %p\n", &arr+1);
 return 0;
}

The result of this code is obvious

  actually ：& The array name represents the address of the whole array , When the address of the array +1 When , Skip the size of the entire array . So the difference is 40 了

Array pointers are applied to instances of two-dimensional arrays

3. Pointer array

We have already talked about , Pointer array is an array of pointers .

 

4. Array parameter passing and pointer parameter passing

  When the array name is passed in , Function arguments, whether array 、 The pointer 、 Or a pointer [ ] It's all right

When you pass in the array name of the pointer array , Then we need to use the secondary pointer , Point to the address of the pointer .

Two dimensional array ：

  When passing parameters with a two-dimensional array , The same as the previous initialization , The number of columns must be given , Otherwise, it's wrong .

and int *arr [ ] This is a pointer error , The elements inside are pointers , So it must be wrong .

int *arr The error is because the first element of a two-dimensional array is a row , You can't receive a line with a pointer . 

Receiving with a secondary pointer must also be , FALSE , Because it's the address of the element , And elements are shaping .

   

5. A function pointer

A function pointer is a pointer used to store the address of a function .

In the form of ： return type +（* Array name ）（ Function parameter type ）

void (*pf)(int , int);

Why use （） Give Way * Combine... With function name first ？ The principle is the same as that of array pointers , because （） Higher priority , Will preferentially combine with parameters , So it becomes a function .

It doesn't matter whether the name of the parameter is written or not .

 

 

  In use , This * It's optional , The two lines with horizontal lines in the picture have the same effect . Even you can use ****** It's all right . 

 

6. Function pointer array

  An array is full of function pointers , Then this array is the function pointer array .

  The code above shows .

Why do we have to [ ] Put it in parentheses ？ Because its nature is an array , So the name is to be with [ ] Combined first .

 

7. A pointer to an array of function pointers

The pointer to the bottom row of the array is the pointer to the function .

How to understand this industry ？ Let's dismantle him first

First of all, he is a (*ppfarr), Then his nature is a pointer , Then outside is [ ] Second, his property is an array , Then talk to the outside * combination , So we can understand it as , This is a pointer , Point to an array , Stored in the array is the function pointer .

  

8. Callback function