More Exceptional C++

Chapter 37. Forward Declarations

Difficulty: 3

Forward declarations are a great way to eliminate needless compile-time dependencies. But here's an example of a forward-declaration snare. How would you avoid it?

1. Forward declarations are very useful tools. In this case, they don't work as the programmer expected. Why are the marked lines errors?

   // file f.h
   //
   class ostream;  // error
   class string;   // error
   string f( const ostream& );
   

2. Without including any other files, write the correct forward declarations for ostream and string above.

Solution

• 1. Forward declarations are very useful tools. In this case, they don't work as the programmer expected. Why ...