External variable in c language

[skyr6546]

Extern keyword tell to compiler that this variable is declared in another C file but we can use it in current file

Lets say we have two files
File1.c
File2.c

First method
I have declared x in file 1 and if i want to use x in file 2 I can use but I have to use extern keyword in file 2 to tell the compiler that variable x is already in file 1

File1.c 

int x;
 
int foo(void)
{
    ...
}


File2.C 

 extern int x;
 
int main(void)
{
    x = 5;
    ...
}

Second method

I have declared x in file 1 and if i want to use x in file 2 I can use but I have to use extern keyword in file 1 to tell the compiler that variable x is already in file 1

File1.c 

extern int x;
 
int foo(void)
{
    ...
}


File2.C 
 
  int x;
 
int main(void)
{
    x = 5;
    ...
}

which one is correct method to use extern variable in c file ?

[laserlight]

Both are correct. I mean, you're just regarding one file as the "first" and the other as the "second", then swapping over the designations in the next example.

A more common way of doing this is to place the extern declaration in a header that is then included as needed.

That said, you should avoid global variables, i.e., it should be rare that you even need to use this at all.