C trap - infinite loop problem caused by array out of bounds

一、引入

下面的程序在VSWhat can go wrong with the compiler？运行结果是什么？为什么？

#include <stdio.h>
int main()
{
    
    int i = 0;
    int arr[] = {
    1,2,3,4,5,6,7,8,9,10};
    for(i=0; i<=12; i++)
    {
    
        arr[i] = 0;
        printf("hello\n");
    }
    return 0;
}

运行结果：

如下图：代码死循环

二、代码缺陷

上述代码有两个问题：

1. 数组访问越界
2. 死循环

三、为什么会死循环？

1、i和arr都是局部变量,Local variables in memory are stored in the stack area.

2、数组随着下标的增长,地址是由低到高变化的.

3、The memory specification of the stack area：先使用高地址处的空间,再使用低地址处的空间.

根据上述代码可知,The program will first create a variable at a high address in the stack areai开辟空间,Then in the stack area, from high to low, it is an arrayarr开辟空间

如下图

By debugging we can observe the following changes in memory：

for循环中,i 的内容是从0,一直增加到12,而数组只有10个空间,因此会越界,每次访问arr数组i号位置时,都会将该位置内容设置为0,当访问到arr[12]时,也会将该位置内容设置为0,而位置恰好为i的位置,即arr[12]恰巧将i设置为0,因此造成死循环.

四、补充说明

The above code has different effects in different compilers,And it is related to the operating environment.

• 在VS2013/2019/2022的x86环境中,i和arrtwo integers apart.即i<=12就死循环
• 在gccThe space in the middle is separated by an integer.即i<=11就死循环
• 在VC6.0There is no extra space in between.即i<=10就死循环

五、总结

We may encounter various problems when writing code：语法错误、编译错误、运行错误……
But we are makingBugAt the same time, try to be one Bug终结者.
学会发现问题,Solving problems and avoiding them are fundamental qualities of a qualified programmer.This requires us to master certain debugging skills,养成良好的编程习惯.