Why does the "static" keyword have so many meanings in C and C++? [duplicate]

Question

As we know, the keyword static has multiple meanings in C. C99 added the possibility of legally writing

void foo (int arr[static 50]) {     // ... } 

which adds to the confusion, and C++ has static member variables and functions.

This would not be so troublesome if all the uses could be connected in some way, but I find it hard to find that link for some of the cases. Particularly why the static keyword should be used to modify visibility (linkage), or what on earth it's got to do with an array's minimum amount of elements.

So is there a historical reason for the abuse of the static keyword, or is there a secret link under the hood that connects all of its uses?

Answer 1

Adding new keywords to a language breaks backwards compatibility. So static gets used where its use might possibly mean something ( int arr[static 50] vs int arr[auto 50] or int arr[extern 50] ) and cannot syntactically appear in that location based its use in previous versions.

Though in that case adding a not_less_than context sensitive keyword in that position would not break previous code, it would add another keyword (so simple text editors which are keyword aware but not syntax aware would not know whether or not it is a keyword), and break the 'keywords are not context sensitive' simplification made in C.

Answer 2

There is a very simple way of remembering of all 3 C++ meanings of static I'm aware of. static means "pretty much like global variable/function but only available directly in scope of..."

• "...this file" if it is in global scope.
• "...this function" if it is in a function (including member functions). Note that if you make classes and lambdas in a function, they are still in this scope. Lambda with an empty capture can access static variable of its "parent" function.
• "...this class" if it is in a class (including those declared with struct). This case is slightly different as you can access the variable/function through an object or by prefixing, but this is a little like asking the class or its object to provide you access to it, and it in fact can be denied (with private). So the access isn't "direct".

In case of the presented C99 array syntax, this is something completely different and I assume it was there to not introduce new keywords, as others suggest.