Array out of bounds

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

Catalog

  One 、 Why is the array accessed out of bounds , Will visit i Variable space ？

  Two 、 Why does the compiler not report an error when accessing beyond the boundary ？

  One 、 Why is the array accessed out of bounds , Will visit i Variable space ？

The first point ： Local data is stored in the stack , The rule of using memory in stack area is to allocate memory space with high address , Allocate memory space from high to low .

Second point ： The variable we created in this problem i And integer arrays are local , Because they are all created in braces , Therefore, the memory in the stack area will be allocated , Put their data on the stack , So the compiler will be assigned to i Variable high address space , The space allocated to the array is i Below the variable space .

The third point ： The subscript of the array changes as the address increases , Subscripts vary from low to high , So when the array is accessed beyond the bounds , It will be possible to access i Variable space .

Drawing interpretation ：

Be careful ： Each compiler allocates memory differently , stay vs2019 in , We created based on this problem i Variables and arr The space occupied by the array is different 2 An integer byte size space , But in other compilers , Maybe not 2 Bytes of space .

This array access is a coincidence , yes C A trap of language , stay 《C Pitfalls and pitfalls 》 This book talks about .

You can imagine , Array cross-border access is actually breaking into someone else's home , And this cross-border visit , I visited my relatives , But it's not my home after all .

  Two 、 Why does the compiler not report an error when accessing beyond the boundary ？

The compiler will not report all the errors you write , If he will report all the mistakes , What else should programmers do ？

The compiler can be compared to a policeman , Mistakes in the program are compared to thieves , It is impossible for the police to catch all the thieves , This is unrealistic .