Nested Class Definition in source file

Question

If I have a nested class like so:

  class MyClass   {     class NestedClass     {     public:       // nested class members AND definitions here     };      // main class members here   }; 

Currently, the definitions of MyClass are in the CPP file but the definitions for NestedClass are in the header file, that is, I cannot declare the functions/constructors in the CPP file.

So my question is, how do I define the functions of NestedClass in the cpp file? If I cannot, what is the reason (and if this is the case, I have a vague idea of why this happens but I would like a good explanation)? What about structures?

Answer 1

You can. If your inner class has a method like:

  class MyClass   {     class NestedClass     {     public:       void someMethod();     };      // main class members here   }; 

...then you can define it in the .cpp file like so:

void MyClass::NestedClass::someMethod() {    // blah } 

Structures are almost the same thing as classes in C++ — just defaulting to 'public' for their access. They are treated in all other respects just like classes.

You can (as noted in comments) just declare an inner class, e.g.:

class MyClass   {     class NestedClass;     // blah }; 

..and then define it in the implementation file:

class MyClass::NestedClass {   // etc. };