Question

I came across a function with this signature.

void foo(char (&x)[5])
{
}

This is the syntax for passing a fixed size char array by reference.

The fact that it requires parentheses around &x strikes me as unusual.

It is probably part of the C++03 standard.

What is this form called and can anyone point out a reference to the standard?

c++decl is not a friend yet:

$ c++decl 
Type `help' or `?' for help
c++decl> explain void foo(char (&x)[5])
syntax error

Answer 1

There is nothing unusual or new about the syntax. You see it all the time in C with pointers. [] has higher precedence than &, so you need to put it in parentheses if you want to declare a reference to an array. The same thing happens with * (which has the same precedence as &): For example, to declare a pointer to an array of 5 chars in C, you would do char (*x)[5];. Similarly, a pointer to a function that takes and returns an int would be int (*x)(int); (() has same precedence as []). The story is the same with references, except that references are only on C++ and there are some restrictions to what types can be formed from references.