c - Use of 'extern' keyword while defining the variable

Question

After seeing this answer I have this doubt. In my project, I have seen some extern variables declared and defined like below:

file1.h

extern int a;

file1.c

extern int a=10;

But in the link I mentioned it says that in the c file it should be defined like:

int a = 10;

Does adding extern key word during the definition too has any purpose/meaning. Or does it matter by the way?

Answer 1

It does not change the meaning. extern only makes sense when you declare a variable. Defining a variable with extern is the same because all global variables that are not marked static are symbols visible to the linker by default.

Note that if you didn't want to initialise the variable, that is, not having the part = 10, the compiler will assume that extern int a is always a declaration and not a definition. In the same sense, having int a globally is always a definition and not just a declaration.