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Tip of the Day
Language: C++
Expertise: Intermediate
Apr 10, 1998

Turning a global function into a file-local function

In standard C, a function declared static has an internal linkage; it is accessible only from within the translation unit (source file) in which it is declared, but not from anywhere else. This technique is used to support information hiding as in the following case:
 
//File hidden.c

static void decipher(FILE *f);//accessible only from within this file

//now use this function in the current source file

decipher ("passwords.bin");

//end of file 
Though still supported in C++, this convention is now considered deprecated, so future releases of your C++ compiler may issue a warning message when finding a static function which is not a member of a class. In order to achieve the same effect in C++ (i.e., when migrating legacy C code), you should use a nameless namespace instead:
 
//File hidden.cpp

namespace { //nameless

void decipher(FILE *f); //accessible only from within this file

}

//now use this function in the current source file. No need for any //'using' declarations or directives.

decipher ("passwords.bin");


//end of file
 
It is guaranteed that nameless namespaces in different source files are unique, so if you declare yet another decipher(FILE*) function within a nameless namespace in another file, the two decipher functions are hidden from each other and hence, do not collide.
Danny Kalev
 
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