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.