Question

What are disadvantages of using static variables like in following code:

namespace XXX
{
    static int i;
    class YYY
    {
        static m_i;     
    };
}

Is using static variables only in .cpp (so they are invisible to other code) file OK?

Answer 1

Various things allowed by C++ represent choices and compromises in software design. There is nothing inherently, absolutely evil about any of them (except perhaps throw specifications, which Prof. Stroustrop deems a broken facility ;-P).

Whether this particular code is a good choice in a particular situation depends on many factors. For example:

• there’ll only be one copy shared by the entire program
  • may be ideal, e.g. you want to have some program-wide modal state
  • terrible: code setting/using the value may find other code has modified it meanwhile (this gets increasingly likely as the program gets larger and more complex)
  • terrible: in multi-threaded code you must use locking and/or atomic operations to avoid data corruption and consequent erroneous behaviour and/or crashes
• being static:
  • other translation units won’t have access to it
  • it won’t pollute the symbol table exposed by a good IDE etc.

In short, if you realise that namespaces and static just reduce identifier clashes, they’ve got all the other pros/cons associated with global variables….