decltype error C2440 cannot convert from 'int *' to 'int *&'

Question

The following is a contrived example of the actual code:

int** Ptr = 0;
decltype(Ptr[0]) Test = (int*)0;

I get the error:

Answer 1

In addition to all the other answers, you may also just use

int ** ptr = 0;
decltype(+ptr[0]) test = (int*)0;
// (+*p) is now an r-value expression of type int, rather than int&

Some of the rules used here are:

• if the value category of expression is lvalue, then decltype yields T&;
• if the value category of expression is prvalue, then decltype yields T.

Also note that if the name of an object is parenthesized, it is treated as an ordinary lvalue expression, thus decltype(x) and decltype((x)) are often different types. [an excerpt from https://en.cppreference.com/w/cpp/language/decltype]

seen at http://www.cplusplus.com/forum/beginner/149331/
more on decltype here : https://en.cppreference.com/w/cpp/language/decltype