How do you tell the compiler to make a member function inline?, C++ FAQ

C++ FAQ / Section 9 / FAQ 9.7

Section 9:

9.1	What's the deal with `inline` functions?
9.2	What's a simple example of procedural integration?
9.3	Do `inline` functions improve performance?
9.4	How can `inline` functions help with the tradeoff of safety vs. speed?
9.5	Why should I use `inline` functions instead of plain old `#define` macros?
9.6	How do you tell the compiler to make a non-member function `inline`?
9.7	How do you tell the compiler to make a member function `inline`?
9.8	Is there another way to tell the compiler to make a member function `inline`?
9.9	What's a good way to define inline member functions outside the class body?

[9.7] How do you tell the compiler to make a member function inline?

When you declare an inline member function, it looks just like a normal member function:

class Fred {
public:
  void f(int i, char c);
};

But when you define an inline member function, you prepend the member function's definition with the keyword inline, and you put the definition into a header file:

inline
void Fred::f(int i, char c)
{
  ...
}

It's usually imperative that the function's definition (the part between the {...}) be placed in a header file. If you put the inline function's definition into a .cpp file, and if it is called from some other .cpp file, you'll get an "unresolved external" error from the linker.