Question

Can you figure out what is wrong with the statement below?

GCC error states:

‘type name’ declared as function returning array

#define MACRO(a) (a)[1]

class index {
public:
    typedef int index_type[2];
    const index_type& operator[](int i) const;
};

int k = 0;
int i = MACRO(index()[k]);

btw: I know what is wrong, I thought it was amusing thing to share. Many thanks to litb, his explanation of previous gotcha helped to solve this error pretty quickly.

Answer 1

In the expanded line:

int i = (index()[k])[1];

(index()[k]) is interpreted as a cast expression, declaring a function that returns an array of length k of index. At least, that’s what it looks like is happening. How gcc is manages to validly interpret the [1] as an expression, I’m not sure.