Limiting Scope of #include Directives

Question

Let's say I have a header file with a class that uses std::string.

#include <string>

class Foo
{
     std::string Bar;

     public:

     // ...
}

The user of this header file might not want std::string to be included in his/her project. So, how do I limit the inclusion to just the header file?

Answer 1

The user of your class must include <string>, otherwise their compiler will not know how big a Foo object is (and if Foo's constructors/destructors are defined inline, then the compiler also won't know what constructor/destructor to call for the string member).

This is indeed an irritating side-effect of the C++ compilation model (basically inherited intact from C). If you want to avoid this sort of thing entirely, you probably want to take a look at the PIMPL idiom.