Can You Inline Member Functions Defined in .cpp Files?

Placing Inline Member Function Definition in .cpp File

In this article, we will address the dilemma of implementing inline member functions in .cpp files despite the convention of placing them in headers.

The issue arises from circular inclusion, as demonstrated by the code snippets below:

<code class="cpp">// File A.h
#include "B.h"

class A {
    B b;
};</code>

<code class="cpp">// File B.h
#include "A.h" // forward declaration

class B {
    inline A getA();
};</code>

Due to the circular dependency, the implementation of getA() must be placed in B.cpp:

<code class="cpp">// File B.cpp
#include "B.h"
#include "A.h"

inline A B::getA() {
    return A();
}</code>

Will the Compiler Inline getA?

No, unless the use of getA() is within B.cpp itself.

Significance of Inline Keywords

The inline keyword in the definition outside the class body is most significant.

Alternative Ways to Define Inline Member Functions in .cpp Files

Unfortunately, there is no alternative approach to placing the definition of an inline member function in its .cpp file. The standard requires the compiler to see the function definition wherever it is called.

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