[Cs3] Extern question

[Mikhail Nesterenko]

Garnica, Ramsey wrote:
> Hello Professor,
> 
> 
> I was looking up examples of extern and one person made an analogy
> that I was wondering if you thought was a good analogy or not.
> 
> 
> Everybody was comparing extern to a global variable in a header file
> and one person made the analogy that prototypes are like extern
> statements for functions.  That seems like a correct analogy to me
> so I was wondering if that is a correct way to think about externs?
> 

It is correct in the sense that both prototypes for functions and
externs for global variables are declarations rather than definitions.

A good use of extern is this:


header1.h
---
extern int i; // tells compiler that global variable "i" is defined somewhere
---



source1.cpp
---
#include "header1.h"

int i=0; // declaration and even initialization of global variable "i"
---


source2.cpp
---
#include "header1.h"

int myfunc(){

    cout << i; // usage of global variable, the compiler knows
               // about "i" from header's declaration
}
---