9. Pointer of C language (2) wild pointer, what is wild pointer, and the disadvantages of wild pointer

This article is the... Of the pointer series 2 piece , If it feels good , You can follow and collect , It will be updated continuously in the future  

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The wild pointer is The position of the pointer is unknown （ Random 、 incorrect 、 There is no definite limit to ） If the pointer variable is not initialized when it is defined , Its value is random , The value of a variable is the address of another variable , It means that the pointer points to a variable whose address is uncertain , To dereference is to access an uncertain address , So the result is unknowable .

We watch through code

#include <iostream>
#include <stdio.h>
using namespace std;
int main(){
    int *p; // Defining pointer variables p
    //*p Representative to p The content of the address is the variable 
    int i = 5;    
    *p =i;// Wild pointer 
}

When we define variables , The operating system assigns addresses to variables , There are two variables in the code , Pointer to the variable p And integer variables i

If we don't assign values to variables , The variable will be randomly assigned a value , Also called garbage value .

Usually , We are defining pointer variables p after , It should be assigned a value , such as p = &i; such p It points to i

But in the code above , We didn't give p assignment ,p The address stored in it is a random garbage value

Through this garbage value address , That is, through *p, We found an unknown variable , If this unknown variable is modified at this time , We may cause the computer to crash , We may have changed important resources . Such behavior is not allowed

In some editors, such as VC6.0 There may be a mistake , There will be no error in some editors

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summary

        Wild pointer is a dangerous behavior , We must be careful when defining pointer variables , Remember to assign a correct value to the pointer variable .