why not exist mutiple definition error when define method in class in c++?

Question

I had one class with test method with body;

class Object {
public:
    Object(){

    }
    virtual ~Object(){

    }

    void test(){
    }
};

I include this object.h in 2 cpp files. Why is there no multiple definition error for functions Object::test that is available (after include) in both cpp files?

I understand that a function with complete body is a definition and not declaration, so I expect there should be multiple definition error.

is there official article talk about it?

It's because test() is [inline](http://en.wikipedia.org/wiki/Inline_function). — Andy Brown, Sep 26 '14 at 07:46
In-class function definitions are implicitly `inline`. `inline` means "may have more than one definition, as long as all definitions are identical". — Mankarse, Sep 26 '14 at 07:46

score 3 · Answer 1 · edited Jun 20 '20 at 09:12

3

According to the C++ Standard (7.1.2 Function specifiers)

3 A function defined within a class definition is an inline function.

4 An inline function shall be defined in every translation unit in which it is odr-used and shall have exactly the same definition in every case (3.2).

And

A function whose name appears as a potentially-evaluated expression is odr-used if it is the unique lookup result or the selected member of a set of overloaded functions (3.4, 13.3, 13.4), unless it is a pure virtual function and its name is not explicitly qualified.

Where ODR is an abbrevation of the One Definition Rule. Simply speaking a function is odr-used when it takes part in expressions that are evaluated.

edited Jun 20 '20 at 09:12

Community

1
1

answered Sep 26 '14 at 07:57

Vlad from Moscow

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Not clear what it is saying :( what is odr-used – Nayana Adassuriya Sep 26 '14 at 08:10
@NayanaAdassuriya There's an [answered question about odr-use](http://stackoverflow.com/questions/19630570/what-does-it-mean-to-odr-use-something) here on SO. – Angew is no longer proud of SO Sep 26 '14 at 08:17

why not exist mutiple definition error when define method in class in c++?

1 Answers1