| extern | Keyword

Keyword Index

Indicates that an identifier is defined elsewhere.

Keyword `extern` indicates that the actual storage and initial value of a variable, or body of a function, is defined elsewhere, usually in a separate source code module. So, it may be applied to data definitions and function prototypes:

    extern data-definition;
    extern function-prototype;

For example,

    extern int _fmode;
    extern void Factorial (int n);

The keyword `extern` is optional (i.e. default) for a function prototype.