Knowledge points that are not well known and useful in CPP programming

I. extern syntax

extern can be placed before a variable or function to represent the definition of a variable or function in another file, prompting the compiler to find its definition in other modules when it encounters this variable or function. In addition, extern can also be used to specify links.

1. When two files have a variable name of the same name at the same time, they can be compiled separately, but when they are linked, they cannot be compiled.
Since the link indicates that this is a program, a program cannot have two variables of the same name.

You can then use extern to tell one of the files to use a variable of the same name as another file.

2, extern "C"

Knowledge points that are not well known and useful in CPP programming