Are static functions acceptable practice for certain things in c++?

Question

Sometimes, for certain things like writing a line to a console, feels like something that should be globally accessible to all objects. Something like:

writeError("UNHANDLED EXCEPTION",someData);

Also things such as math functions feel this way too. But how do you draw the line when doing this sort of thing becomes bad practice?

Static functions are not globally accessible. They are local for translation unit. — Tadeusz Kopec for Ukraine, Jun 01 '11 at 13:23
In fact I think it's best not to refer to free functions defined with keyword `static` (to give them internal linkage) as "static functions". It's confusingly similar to the use of "static" in "static member functions", whereas actually C++ is using one keyword for two unrelated things. — Steve Jessop, Jun 01 '11 at 13:40

score 10 · Accepted Answer · edited May 23 '17 at 11:45

Some people draw the line at the point where the non-member function needs to be a friend of one of its arguments, so they use a lot of free functions.

Some people draw the line at the point where the non-member function could reasonably be a member function of one of its arguments, even though it doesn't actually use the class internals. They have somewhat fewer free functions.

It's usually best not to think of this as "becoming bad practice" - not all design in C++ is "properly" object-oriented. If your task is best solved by means other than OOP, then using OOP is itself "bad practice". The argument how best to design your code can go on indefinitely in any language, but C++ doesn't make any particular effort to steer you towards writing classes.

See also:

Effective C++ Item 23 Prefer non-member non-friend functions to member functions

To illustrate the OOP issue: a class method depends (implicitly) on the class internals. A free function, however, may only access the class public API. This reduces coupling / enhances encapsulation: thus it's easier to change the class internals, assert the class invariants, etc... — Matthieu M., Jun 01 '11 at 14:08

score 6 · Answer 2 · answered Jun 01 '11 at 13:23

Global APIs of this nature are just fine.

The best practice these days being to wrap them in a namespace:

namespace LOGGING { 
     void writeError(message, ...); 
}

Making something static in C++ is not the same thing as making something static in Java. In C++, a static function is only visible from that compilation unit (.cpp file). It does not make it a global non-class function.

A static member function in C++ however, is the same in Java - it allows it to be called from outside of an object context class::method(params) instead of classObject.method(params).

score 1 · Answer 3 · answered Jun 01 '11 at 13:56

There are two questions here :

Are static functions acceptable practice for certain things in c++?

Yes, some things can only be archived using functions. For example, registering to glut callbacks.

Also things such as math functions feel this way too. But how do you draw the line when doing this sort of thing becomes bad practice?

Also, operators on classes can be functions (for example operator +, taking two operands, or stream operator. How to draw a line? I guess do enough of bad things to identify what is bad and what is good. Gain experience enough experience and you'll know. My advise is to try to fully unit test your code. Having long and complex unit tests, or not able to easy unit test something is usually a sign of a problem.

+1 interesting point - unit tests as a criterion for good design — davka, Jun 01 '11 at 14:32

Are static functions acceptable practice for certain things in c++?

3 Answers3