C++ Primer 4/e在Namespaces這個地方有一段說明：『Prior to the introduction of namespaces in standard C++, programs had to declare names as static to make them local to a file. The use of file statics is inherited from C. In C, a global entity declared static is invisible outside the file in which it is declared.
警告
The use of file static declarations is deprecated by the C++ standard. A deprecated feature is one that may not be supported in future releases. File statics should be avoided and unnamed namespaces used instead.』
中文版的這樣寫：『標準C++引入namespace之前，程式必須將某個名稱宣告為static才能使它區域化（local to）於檔案內。這種性質繼承自C語言。在C語言中，宣告為static的global物體，在其所處檔案之外是不可見的。
警告
C++不贊成使用file static變數宣告。這意味C++將來有可能不再支援此一特性。』
還好我static也很少用。