为什么有时对变量的引用表现为大小为1的数组？

Question

#include <iostream>
using namespace std;

void outputFirst(int x[]) {
    cout << x[0] << endl;
}

int main() {
    int x = 40;

    // works
    outputFirst(&x);

    // works
    int *y = &x;
    cout << y[0] << endl;

    // invalid types ‘int[int]’ for array subscript
    cout << &x[0] << endl;

    return 0;
}

Why can I use a reference to an int as an array when I pass it to a function or assign it to another variable first, but not directly?

I'm using g++-6.3.

Answer 1

Why can I use a reference to an int

Note that &x doesn't mean reference to x , it means taking the address of x and you'll get a pointer (ie int* ) from it. So int *y = &x; means taking the address from x , then y[0] means get the 1st element of the array pointed by the pointer (as if it points to the 1st element of the array which contains only one element (ie x ) ), so at last it returns x itself.

And about why &x[0] doesn't work, note that operator[] has higher precedence than operator& . Then &x[0] is interpreted as &(x[0]) , while x[0] is invalid since x is just an int .

You should add parentheses to specify the precedence explicitly, eg

cout << (&x)[0] << endl;