I have heard that functions in are called "extern" by default. So, according to this the scope of functions should be inside, entire the project, isn't it? I believe haven't seen this. I just like to know that is it really visible across the project files by default?
The article link: https://www.geeksforgeeks.org/understanding-extern-keyword-in-c/
It says:
" First, Let’s consider the use of extern in functions. It turns out that when a function is declared or defined, the extern keyword is implicitly assumed. When we write.
int foo(int arg1, char arg2);
The compiler treats it as: extern int foo(int arg1, char arg2);
Since the extern keyword extends the function’s visibility to the whole program, the function can be used (called) anywhere in any of the files of the whole program, provided those files contain a declaration of the function. (With the declaration of the function in place, the compiler knows the definition of the function exists somewhere else and it goes ahead and compiles the file). So that’s all about extern and functions. "
Yes all functions (if there is no other modifier) are implicitly extern. You may alter it with static modifier, which makes the function visible only for the file it is written in. Another quite common use is extern inline which makes inline functions visible for another files, not just the module they are defined in.