In English, the word “static” has a variety of meanings, but they can be summed up by the definition of the adjective: “pertaining to or characterized by a fixed or stationary condition”. In the software world, it generally refers to things that do not change over time. In both cases, the opposite may be “dynamic”.<\/p>\n
In C and C++, the keyword static<\/strong> is inspired by the broader meaning of the word, but has two, separate uses. In C++, there is even a third use of the keyword. The nuances of these meanings\/uses are not always well understood …<\/p>\n In C\/C++, when you declare a variable [or instantiate an object], the location of the declaration implies the scope of the variable and where in memory it is stored. For example:<\/p>\n The variable x<\/strong> has a scope which renders it visible to any function following it in this module and any function in any other module. It is stored in static memory – i.e. not on the stack or in a register. The variable y<\/strong> is only available within the function fun()<\/strong> and is stored on the stack or in a register. The scope of x<\/strong> is now restricted to functions following it in this module and it is not available to functions outside of this module. Its storage is unchanged. The scope of y<\/strong> is unchanged, but it is now stored in static memory.int x;\nvoid fun()\n{\n int y;\n ...<\/pre>\n
\nIf we modify the code thus:<\/p>\nstatic int x;\nvoid fun()\n{\n static int y;\n ...<\/pre>\n
\nNotice how the same keyword changed the scope of an external variable and the storage of an automatic variable, even though these are quite different attributes of the variables. I feel that an addition keyword local<\/strong> would be useful to adjust the scope of an external variable.
\nIn C++, there is a third use for the static<\/strong> keyword. It can be used to share a member variable among instances of a class. For example:<\/p>\nclass c\n{\n static int z;\n ...<\/pre>\n