C Programming - Declarations and Initializations - Discussion

Is the variable declared as extern similar to the variable declared under main?

What is the global function?

What we declare before the main function it is called global declaration. Then we can use that variable any where in the program. If we declare the variable inside the main function it is called locally declaring the variable. We can use that variable only in specified function not out side the main function.

What is the difference between int main and extern int main?

Extern is a keyword, which informs the compiler that the function or variable has external linkage.

The syntax is:

extern string-literal { declaration-list }
extern string-literal declaration

In C there are four storage classes.

1) Automatic = Auto, its lifetime is within the fun. By default it is garbage initialization.

2) Static = Life cycle of static is throughout the program, default value is 0.

3) Extern = It is global variable. Outside the function, treated as global variable only.

Ex:

int a;(global variable)
main()
{
a=4; (local variable)
printf(a);
mdify();
printf(a);
}
modify()
{
a=a+1;
printf(a)
}

Hope it is clear.

What is the different between normal function and extern function?

Can anyone tell me how can we access one C program to another one with external variable.

Oh horrible explanation. By declaring a variable as an extern, you just tell the compiler that a variable has been declared. Without an extern, something like this:

int x;

The compiler declares as well as defines (i.e, allocates memory to the variable x). No wonder why extern is used in declaring a variable that's gonna be used across various files.

Please explain function using extern keyword with proper example.