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

C++ FAQ / Section 9 / FAQ 9.6

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?

[9.6] How do you tell the compiler to make a non-member function inline?

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

void f(int i, char c);

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

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

Note: It's imperative that the function's definition (the part between the {...}) be placed in a header file, unless the function is used only in a single .cpp file. In particular, if you put the inline function's definition into a .cpp file and you call it from some other .cpp file, you'll get an "unresolved external" error from the linker.