C++ 文件布局

3. 自动售票机例子

• TicketMachine.h

#ifndef TICKETMACHINE_H_
#define TICKETMACHINE_H_

class TicketMachine {
public:
    TicketMachine();
    virtual ~TicketMachine();

    void showPrompt();
    void insertMoney(int money);
    void showBalance();
    void printTicket();
    void showTotal();
    
private:
    const int PRICE;
    int balance;
    int total;
};

#endif

• TicketMachine.cpp

#include <iostream>
#include "TicketMachine.h"

TicketMachine::TicketMachine() : PRICE(0) {

}

TicketMachine::~TicketMachine() {

}

void TicketMachine::showPrompt() {
    std::cout << "prompt: " << std::endl;
}

void TicketMachine::insertMoney(int money) {
    balance = 0;
    balance += money;
}

void TicketMachine::showBalance() {
    std::cout << "balance: " << balance << std::endl;
}


int main()
{
    TicketMachine tm;
    tm.insertMoney(100);
    tm.showBalance();
    return 0;
}

3.1 :: 解析符(resolver)

• <Class Name>::<function name>

• ::<function name>

• demo.cpp

void S::f() {
    ::f(); // 会递归调用自己
    ::a++; // 默认使用全局的 a
    a--;  // The a at class scope
}

3.2 定义类

• In C++, seperated .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).

3.2.1 头文件

• 函数：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.
• 类：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.

3.2.2 头文件 = 接口(Header = interface)

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

3.2.3 C++ 代码组织结构

• a.h
• a.cpp
• include: 是把 a.h 的内容插入到a.cpp

• a.h

void f();

int global;

• a.cpp

#include "a.h"

int main()
{
    return 0;
}

3.2.3.1 查看预编译结果

• 第一种方式：cpp a.cpp，会将结果直接打印在控制台；

• 第二种方式：g++ a.cpp --save-temps,然后，使用more a.ii，查看a.ii文件内容

• a.ii

# 1 "a.cpp"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "a.cpp"
# 1 "a.h" 1
void f();

int global;
# 2 "a.cpp" 2

int main()
{
    return 0;
}

3.2.3.2 声明(declaration)和定义(definition)

• b.cpp

#include "a.h"

void f(){

}

1，共同编译 a.cpp和b.cpp: g++ a.cpp b.cpp
2，出现异常信息：

3，a.h文件中int global;是定义，可以增加关键字“extern”，由“definition”调整为“declaration”

• a.h

void f();

extern int global;

4，调整b.cpp

• b.cpp

#include "a.h"

void f(){
    global++;
}

5，编译：g++ a.cpp b.cpp，出现异常：

6，继续调整b.cpp

• b.cpp

#include "a.h"

int global;

void f(){
    global++; 
}

3.2.4 Declarations vs. Definitions

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

3.2.5 #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>

3.2.6 标准 .h 文件结构

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

#ifndef HEADER_FLAG
#define HEADER_FLAG

// Type declaration here ...

#endif // HEADER_FLAG

参考资料：

• 浙江大学 C++ 翁恺