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C++之 头文件

2024-07-30 17:17:32   223人阅读

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

C++之 头文件


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