C++之 头文件

bash:

g++ a.cpp b.cpp --save-temps -Wall

Definition of a class

• In C++,separated .h and .cpp files are used to define one class.
• Class declaration and prototypes in that class are in the header file(.h).
• All the bodies of these functions are in the source file(.cpp).

The header files

• If a function is declared in a header file,you must include the header file everywhere the function is used and where the function is defined.
• If a class is declared in a header file,you must include the header file everywhere the class is used and where class member functions are defined.

Header = interface

• The header is  a contract between you and the user of your code.
• The compile enforces the contract by requirig you to declare all structures and functions before they are used.

Declarations vs. Definitions

• A .cpp file is a compile unit
• Only declaratons are allowed to be in .h
• extern variables
• function prototypes  //函数原型
• class/struct declaration

#include

• #include is to insert the included file into the .cpp file at where the #include statement is.
• #include "xx.h":first search in the current directory,then the directories declared somewhere
• #include <xx.h>:search in the specified directories
• #include <xx>:same as #include <xx.h>

Standard header file struct

#ifndef HEADER_FLAG

#define HEADER_FLAG

//Type declaration here...

#endif   //  HEADER_FLAG

Tips for header

1. One class declaration per header file
2. Associated with one source file in the same prefix of file name.
3. The contents of a header file is surrounded with #ifndef #define #endif