Can C99 Arrays Be Sized at Runtime Without Dynamic Memory Allocation?

Understanding Array Size Determination at Run Time without Dynamic Allocation

Seeking clarifications regarding the legitimacy of array size determination at run time without dynamic allocation, it's worth exploring C99's introduction of variable-sized arrays on the stack.

In the provided code snippet:

int main(int argc, char **argv) {
    size_t size;
    cin >> size;
    int array[size];
    ...
    return 0;
}

The array size is dynamically determined at runtime based on the user input stored in the size variable. This behavior is supported by C99, which allows for variable-sized arrays to be declared on the stack.

Unlike dynamic memory allocation using malloc or new, which allocates memory from the heap, variable-sized arrays are allocated on the stack. The compiler adjusts the stack pointer accordingly, similar to how it handles statically-sized arrays (e.g., int array[100]).

It's important to note that variable-sized arrays on the stack are different from dynamically allocated arrays. The former does not involve heap allocation and operates directly on the stack, while the latter uses heap memory.

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