Do Variable Length Arrays (VLAs) in C Contradict Constant Array Bound Rules?

Understanding the Use of Variable Length Arrays (VLAs) with Constant Array Bounds

In C programming, it's commonly understood that array bounds must be specified as constant expressions to ensure memory allocation during runtime. However, an apparent contradiction arises with the following code snippet that seems to work despite violating this rule:

#include <iostream>
using namespace std;

int main() {
    int n = 10;
    int a[n];

    for (int i = 0; i < n; i++) {
        a[i] = i + 1;
        cout << a[i] << endl;
    }

    return 0;
}

This code successfully declares an array of size n and performs operations on its elements without encountering any compilation errors. To resolve this apparent discrepancy, it's essential to delve into the concept of Variable Length Arrays (VLAs).

Role of VLA in the Code Snippet

The C99 standard introduced VLAs, allowing arrays with variable lengths based on values known at runtime like the above n. This feature is supported in certain compilers, including some C compilers, which enables the allocation of arrays of variable size on the stack.

In the given code, the line int a[n]; declares a VLA with a size determined by the n variable's value at runtime. This allocation on the stack enables the code to work effectively, similar to how it would if the array was explicitly declared as int a[10].

While this feature can offer flexibility in certain scenarios, it's crucial to note that it may not be supported by all compilers and comes with potential pitfalls. As with any language feature, it's essential to understand its benefits and limitations before incorporating it into code.

The above is the detailed content of Do Variable Length Arrays (VLAs) in C Contradict Constant Array Bound Rules?. For more information, please follow other related articles on the PHP Chinese website!