How to associate non-member functions with a class in Doxygen?

I'm sure there's some way to do this with the \defgroup, \addgroup and \@{ \@} tags, but after a couple of hours of trial and (obviously) error, I'm asking SO.....

I have:

class C {
public:
    void foo () const;
};

and I have some helper non-member functions that really are part of C's interface, but aren't in the class:

std::string
format (const C& c, const std::string &fmt);

I'd like the format function to appear on the same page as the class functions. Is that just not possible? Is th开发者_运维知识库e best I can do a "module" page, which lists C as a class (with a hyperlink to C's comments, and format as a function?

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\relates (or \memberof) seem to be what you are looking for.

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Creating a group and assigning functions outside of your class in that group will work, but in the class documentation itself, you won't get references to your functions unless you use commands such as @see or @sa. Honestly, because a function takes a documented parameter doesn't mean this function is automatically part of the library, but you can link both classes and functions together using @defgroup and @addgroup.