Deep understanding of extern "C"

1. Introduction
C ++ language was originally created as "a better
C ", but this does not mean that the global variables and functions in C ++ are compiled and connected in the same way as those in C. As a language to be compatible with C, C ++ retains the features of some procedural languages (known as "incomplete Ground Object "), therefore, it can define global variables and functions that do not belong to any class. However, C ++ is an object-oriented ProgramThe design language. In order to support function overloading, C ++ treats global functions differently from C.
2. Start with the standard header file
An enterprise once gave the following interview question: why do standard header files have a structure similar to the following?
# Ifndef _ incvxworksh
# DEFINE _ incvxworksh
# Ifdef _ cplusplus
Extern "C "{