🌫 Extern Keyword

Extern keyword is used to declare a variable that is outside the file and is defined in another file.

extern tells the compiler that this data is defined somewhere and will be connected with the linker from other produced relocatable object after compilation, during objects linkage (before making executable object file).

https://stackoverflow.com/questions/496448/how-to-correctly-use-the-extern-keyword-in-c/499330#499330