C++ Primer, Fifth Edition

18.1.2. Catching an Exception

The exception declaration in a catch clause looks like a function parameter list with exactly one parameter. As in a parameter list, we can omit the name of the catch parameter if the catch has no need to access the thrown expression.

The type of the declaration determines what kinds of exceptions the handler can catch. The type must be a complete type (§ 7.3.3, p. 278). The type can be an lvalue reference but may not be an rvalue reference (§ 13.6.1, p. 532).

When a catch is entered, the parameter in its exception declaration is initialized by the exception object. As with function parameters, if the catch parameter has a nonreference type, then the parameter in the catch is a copy of the exception object; changes ...