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c++operatorsnamespacesconventions
Anycorn
Anycorn

Reputation: 51435

Which namespace does operator<< (stream) go to?

If I have have some overloaded ostream operators, defined for library local objects, is its okay for them to go to std namespace? If I do not declare them in std namespace, then I must use using ns:: operator <<.

As a possible follow-up question, are there any operators which should go to standard or global namespace?

Upvotes: 16

Views: 4058

Answers (4)

Herb Sutter
Herb Sutter

Reputation: 2639

operator<<( ..., MyClass ) should go in the same namespace as MyClass. You should think of it as part of the interface of MyClass, even though it happens to be (necessarily) a non-member function.

A couple of references:

Upvotes: 25

John Dibling
John Dibling

Reputation: 101446

The C++ Standard explicitly forbids you from declaring your own constructs in the std namespace.

Upvotes: 8

Kirill V. Lyadvinsky
Kirill V. Lyadvinsky

Reputation: 99535

According to Koenig Lookup (C++ Standard 3.4.2) operator<< will be searched in namespaces of arguments. No need to declare it in std namespace.

Upvotes: 26

JaredPar
JaredPar

Reputation: 754535

It is generally a bad practice to declare anything (types, operators, etc ...) to be a part of a namespace you do not own. This can have unexpected consequences for people consuming your library. A better solution is to define your own namespace and to import both std and your namespace when you need to combine solutions.

Upvotes: 2

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