CODEWITHSUNDEEP
c++statickeywordlinkage
mathematician1975
mathematician1975

Reputation: 21351

Why should we only use 'static' inside a class or a function (C++)?

I was recently reading Stroustrups The C++ Programming Language and in the section about Linkage in chapter 9 I came across the following paragraph:

"In C and older C++ programs, the keyword static is (confusingly) used to mean "use internal linkage". Don't use static except inside functions and classes."

The problem is that reading further on, the author did not elaborate on why this is bad practice. I use static functions from time to time in my code usually for some simple calculation that is not needed outside the compilation unit, but I never realised this was frowned upon and it is not obvious to me why it is bad. Can anyone shed light on this for me please??

Upvotes: 6

Views: 239

Answers (2)

Matteo Italia
Matteo Italia

Reputation: 126957

I think that the idea is not to frown upon internal linkage, but to avoid confusion with the new meaning of static: static has way too many meanings (declaring stuff with internal linkage, defining local variables with static storage duration, marking non-instance members of classes), so avoiding one of the less intuitive ones is a good thing.

Because of this, the C++98 standard provides another way to declare stuff with internal linkage: unnamed namespaces, and deprecates static "when declaring objects in a namespace scope".

The C++11 standard removed this deprecation (and also changed somehow the semantic of unnamed namespaces, not really requiring internal linkage), so it's now really a matter of style.

Upvotes: 5

Luchian Grigore
Luchian Grigore

Reputation: 258678

Because in C++ anonymous namespaces should be preferred, which basically offer the same functionality.

I think static in this context is frowned upon because of the double meanings, and the fact that the two meanings are quite opposite - if inside a class or a struct it represents a global state, whereas outside it gives internal linkeage and provides a copy of a variable or method to each translation unit.

Moreso, static can only apply to functions and variables, whereas inside an anonymous namespace you can have type declarations.

namespace  //OK
{
    class X {};
}

static class X //syntactically correct, but does nothing
{
};

Note that the standard deems the use of static to specify linkeage as deprecated.

Upvotes: 4

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