Why Doesn't Out-of-Bounds Array Access Always Cause a Segmentation Fault in C ?

Accessing Beyond Array Bounds: Why It Doesn't Always Result in a Segmentation Fault

C programmers may encounter perplexing situations where they can access and modify memory beyond the declared size of an array without triggering a segmentation fault. This phenomenon stems from the inherent undefined behavior in such scenarios.

Consider the following code snippet:

#include <iostream>
using namespace std;

int main()
{
    int *a = new int[2];
    a[0] = 0;
    a[1] = 1;
    a[2] = 2;
    a[3] = 3;
    a[100] = 4;
    int b;

    return 0;
}

As observed in the code, the pointer 'a' points to an array of integers with a size of 2. However, values are assigned to indices beyond the valid range of [0, 1]. Surprisingly, this code compiles successfully and executes without generating a segmentation fault.

Why is this behavior possible? In C , accessing memory beyond the bounds of an array is considered undefined behavior. This means that the compiler is not obligated to generate an error or take any specific action. The consequences of such operations are unpredictable and can vary depending on the platform, compiler settings, and specific circumstances.

In this particular case, the code doesn't crash because the accessed memory happens to be accessible and writable. However, this is not a guarantee. In other instances, attempting to access out-of-bounds memory can result in a segmentation fault, program termination, or data corruption.

It's crucial to understand that undefined behavior can lead to unexpected and potentially harmful results. While it may not always trigger an immediate crash, it can introduce hidden bugs and make it challenging to debug the program. Therefore, programmers should always ensure that they access arrays and other data structures within the defined bounds to maintain program integrity and reliability.

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