C++ Cookbook

2.5. Including an Inline File

Problem

You have a number of membe r functions or standalone functions that you want to make inline, but you don’t want to define them all in the class definition (or even after it) in the header file. This way, you keep declaration and implementation separate.

Solution

Create an .inl file and #include it at the end of your header file. This is equivalent to putting the function definition at the end of the header file, but this lets you keep declaration and definition separate. Example 2-6 shows how.

Example 2-6. Using an inline file

// Value.h
#ifndef VALUE_H_  _
#define VALUE_H_  _

#include <string>

class Value {
public:
   Value (const std::string& val) : val_(val) {}
   std::string getVal() const;
private:
   std::string val_;
};

#include "Value.inl"

#endif VALUE_H_  _

// Value.inl
inline std::string Value::getVal() const {
   return(val_);
}

This solution doesn’t require much explanation. #include is replaced with the contents of its argument, so what happens here is that the contents of Value.inl are brought into the header file. Any file that includes this header, therefore, has the definition of the inline functions, but you don’t have to clutter up your class declaration.