Find the cause of program dead cycle through debugging

Tips ： This article is based on VS2022x86 Environmental Science .

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Tips ： The following is the main body of this article , The following cases can be used for reference

One 、 Endless loop code display

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int main()
{
     
	int i = 0;
	int arr[10] = {
      1,2,3,4,5,6,7,8,9,10 };
	

	for (i = 0; i <= 12; i++)
	{
     
		arr[i] = 0;
		printf("hehe\n");
	}
	return 0;
}

This code will not report an error , It will print in an infinite loop hehe.

Two 、 Debug analysis

When i=9 when ,hehe It has been printed nine times , Immediately assign the last element of an integer array with a capacity of 40 bytes to zero , The tenth hehe Also about to print . If the cycle condition at this time is i<10, Then the cycle is about to end . But the cycle condition here is i<=12, After the tenth cycle , For an array that can only store ten elements , Can the program continue ？

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Continue debugging the program .

At this time, it is found that the program is still in progress , Although the array is out of bounds , But after the array , Still open up an area for storage arr[10].hehe Also printed 11 Time . At the same time, it is found that under the subsequent debugging , Find out arr[11] Also successfully stored . As shown below ：

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Then according to this situation , When the cyclic condition i Greater than 12 when , The cycle stops , Print up to 13 Time hehe. Why doesn't the cycle come out , It has been going on ？
Then go on to debug , monitor arr[12].

At this time, we found that , Enter the thirteenth cycle , stay arr[12] Before the assignment ,arr[12] It is not a random value , It's the heel i equally , All values are 12.
Guess after the array goes out of bounds , When the back is arr[12] Is the open area related to i The address of is repeated ？

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In order to confirm the above speculation , We can i The address of arr[12] Take out your address , Observe whether it is the same address .

As shown in the figure , The guess is true .arr[12] The address of i The address of is the same address .
So when arr[12] To be an assignment 0 when ,i Also assigned to zero , The cycle condition returns to the starting point , There's a dead cycle .

3、 ... and 、 reason

Local data is stored in the stack .
1. The usage habit of stack area is to use the space at the high address first , Then use the space at the lower address ,i Variables are created first , Use high address ,arr After being created , Use low address .（ The value of high address in memory is large , The value of low address in memory is small , It is reflected in the above figure ）
2. Arrays grow with subscripts , The address changes from low to high .
3. It can be seen from the above two , When the array is operated out of bounds , The address created after the array may cover i, There may be a dead cycle .