Reusing variable in function parameter list

Question

int doSomething(int n, int arr[n])

What confuses me here is the reusing of the n variable inside the parameter list. Can anyone explain why this is valid and what are the use cases?

Answer 1

It is valid.

For this specific case it is equivalent to:

int doSomething(int n, int arr[]);
int doSomething(int n, int *arr);

because the array parameters are automatically transformed into pointers to arrays' elements. In general there are a few differences between array-like and pointer declarations of parameters. See link for more details.

IMO, the better usage should be:

int doSomething(int n, int arr[static n]);

This static n tell the compilers that at least n elements pointer by arr are valid. Moreover it makes the declaration visually different from a declaration of array what helps to avoid surprising issues when sizeof arr is used.