【新手向】c++把class放到另外的文件里

WARNING: 这篇文档虽然能用, 但是其实有更好的办法, 就是把.cpp改为.hpp, 然后在.h文件的末尾 # include “.hpp”, 在编译的时候只需要g++ main.cpp就行了

你本来的文件长这样

# include <iostream>

class myclass{
    
    
    public:
        int property;
        void say_property(){
    
    
            std::cout << property << std::endl;
        }
};

int main() {
    
    
    myclass i; //i for instance
    i.property = 1;
    i.say_property();
    return 0;
}

---

放到另一个文件里

main.cpp内的处理类似把函数放到另一个文件里，也是在main()前面要写上class的声明，
但是另一个文件里就不太一样了，
不能直接在另一个文件里定义class，而是先声明class再针对未定义的部分使用，myclass::func(){}进行定义。

//>>>cat main.cpp
class myclass{
    
      //仅声明
    public:
        int property;
        void say_property();
};

int main() {
    
    ...

//>>>cat anotherFile.cpp
# include<iostream> 
class myclass{
    
      //仅声明
	...
};

void myclass::say_property(){
    
    ...

>>>g++ main.cpp anotherFile.cpp

---

放到另外两个文件里面

思路和把函数放到另外两个文件里相同，只不过是用一个头文件代替class的声明

//>>>cat main.cpp
# include "whatever.hpp"

int main() {
    
    ...

//>>>cat whatever.hpp
#pragma once

class myclass{
    
       //仅声明
	...
};

//>>>cat anotherFile.cpp
# include "whatever.hpp"
# include <iostream>

void myclass::say_property(){
    
    ...

>>>g++ ...

---

如果你想要更具体的例子, 可以往下继续看

---

//>>>cat main.cpp
# include <iostream>
# include <string>
# include "Meat.h"

void test(){
    
    
    Meat undefinedMeat; //good
    std::cout << undefinedMeat.get_name() << std::endl; //good
    std::cout << undefinedMeat.get_price_per() << std::endl; //good
    std::cout << undefinedMeat.get_n_stored() << std::endl; //good
    std::cout << undefinedMeat.get_price(10) << std::endl; //good

    Meat beef("beef", 300.00, 10); //good
    std::cout << beef.get_name() << std::endl; //good
    std::cout << beef.get_price_per() << std::endl; //good
    std::cout << beef.get_n_stored() << std::endl; //good
    std::cout << beef.get_price(10) << std::endl; //good
    beef.buy(5);std::cout << beef.get_n_stored() << std::endl; //good
}
int main(){
    
    
    test();
    return 0;
}

 //>>>cat Meat.cpp
 # include <string>
# include "Meat.h"

std::string Meat::get_name(){
    
    
    return _name;
}
double Meat::get_price_per(){
    
    
    return _price_per;
}
double Meat::get_price(int n_required){
    
    
    return n_required*_price_per;
}
int Meat::get_n_stored(){
    
    
    return _n_stored;
}
void Meat::buy(int n_required){
    
     //用户输入要买的数量, 然后进行购买, 暂时不考虑交互的问题
    int new_n_stored = _n_stored;
    new_n_stored = _n_stored - n_required;
    set_n_stored(new_n_stored);
}
Meat::Meat():Meat("meat", 30, 10){
    
    }
Meat::Meat(std::string name, double price_per, int n_stored){
    
    
    set_name(name);
    set_price_per(price_per);
    set_n_stored(n_stored);
}

void Meat::set_name(std::string name){
    
    
    _name = name;
}
void Meat::set_price_per(int new_price_per){
    
    
    _price_per = new_price_per;
}
void Meat::set_n_stored(int n_stored){
    
    
    _n_stored = n_stored;
}

//>>>cat Meat.h
# pragma once
# include <string>
# include "Meat.h"

class Meat{
    
    
   public:
       std::string get_name();
       double get_price_per();
       double get_price(int n_required);
       int get_n_stored();
       void buy(int n_required);
       Meat();
       Meat(std::string name, double price_per, int n_stored);
   private:
       std::string _name = "undefined meat";
       void set_name(std::string name);
       double _price_per = 0;
       void set_price_per(int new_price_per);
       int _n_stored = 0;
       void set_n_stored(int n_stored);
};

>>>g++ main.cpp Meat.cpp
>>>./a.out
meat
30
10
300
beef
300
10
3000
5