C++类继承代码编译链接错误求助，附代码及报错信息

问题背景 #

正在学习C++类继承，复制讲师代码后无法编译，项目包含2个.cpp和2个.h文件，以下是所有代码及报错信息：

代码文件 #

Main.cpp

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

int main(){
    Player p1("Basketball");
    std::cout <<"player : " << p1 <<std::endl;

    return 0;
}

person.h

#include <iostream>
#include <string>
#include <string_view>

class Person {
    friend std::ostream& operator << (std::ostream& out, const Person& person);
    public:
    Person();
    Person(std::string& first_name_param, std::string& last_name_param);
    ~Person();

    std::string get_first_name() const{
        return first_name;
    }

    std::string get_last_name() const{
        return last_name;
    }

    private:
    std::string first_name{"Mysterious"};
    std::string last_name{"Person"};
};

player.h

#include <iostream>
#include <string>
#include <string_view>
#include "person.h"

class Player : public Person{
    friend std::ostream& operator << (std::ostream& out, const Player& player);
public:
    Player() = default;
    Player(std::string_view game_param);
    
private:
    std::string m_game{"None"};

};

player.cpp

#include "person.h"
#include "player.h"


Player::Player(std::string_view game_param)
: m_game(game_param){

}

std::ostream& operator<<(std::ostream& out, const Player& player){
    out << "Player: [ game: " << player.m_game << " names: " << Player.get_first_name() << " " << Player.get_last_name() << "]";
    return out;
}

person.cpp

#include "person.h"
 
 Person::Person(){}

Person::Person(std::string& first_name_param, std::string& last_name_param)
    : first_name(first_name_param), last_name(last_name_param) {
    }

std::ostream& operator << (std::ostream& out, const Person& person){
    out << "Person [" << person.first_name << " " << person.last_name << "]";
    return out;
}

Person::~Person(){

}

报错信息 #

Executing task: C/C++: g++.exe build active file 

Starting build...
C:\msys64\mingw64\bin\g++.exe -fdiagnostics-color=always -g C:\Users\DustinB\CodingClass\Inheritance\main.cpp -o C:\Users\DustinB\CodingClass\Inheritance\main.exe
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/12.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\DustinB\AppData\Local\Temp\ccIpfZtM.o:C:\Users\DustinB\CodingClass\Inheritance/main.cpp:11: undefined reference to `Player::Player(std::basic_string_view<char, std::char_traits<char> >)'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/12.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\DustinB\AppData\Local\Temp\ccIpfZtM.o: in function `main':
C:\Users\DustinB\CodingClass\Inheritance/main.cpp:12: undefined reference to `operator<<(std::ostream&, Player const&)'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/12.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\DustinB\AppData\Local\Temp\ccIpfZtM.o: in function `Player::~Player()':
C:\Users\DustinB\CodingClass\Inheritance/player.h:6: undefined reference to `Person::~Person()'
collect2.exe: error: ld returned 1 exit status

Build finished with error(s).

 *  The terminal process terminated with exit code: -1. 

问题解决 #

1. 编译命令错误（核心原因） #

当前编译命令只编译了main.cpp，没有将person.cpp和player.cpp纳入编译链接流程，导致链接器找不到这些文件中实现的函数、构造函数和析构函数。

正确编译命令：

g++.exe -fdiagnostics-color=always -g main.cpp person.cpp player.cpp -o main.exe

2. 代码语法错误 #

在player.cpp的operator<<重载函数中，错误地使用类名Player调用成员函数，成员函数需要通过对象实例调用，应改为player.get_first_name()和player.get_last_name()：

修正后的player.cpp代码片段：

std::ostream& operator<<(std::ostream& out, const Player& player){
    out << "Player: [ game: " << player.m_game << " names: " << player.get_first_name() << " " << player.get_last_name() << "]";
    return out;
}

3. 额外优化建议 #

• 头文件包含保护：在所有头文件中添加包含保护，防止重复包含导致的编译错误，例如在person.h中：

  #ifndef PERSON_H
  #define PERSON_H
  // 原头文件内容
  #endif // PERSON_H
  

  player.h同理添加对应保护宏。
• 构造函数参数优化：将Person构造函数的参数改为const std::string&或std::string_view，这样可以兼容临时字符串，避免不必要的拷贝：

  // 修改person.h中的构造函数声明
  Person(const std::string& first_name_param, const std::string& last_name_param);
  // 或者更高效的版本
  Person(std::string_view first_name_param, std::string_view last_name_param);
  

  同时对应修改person.cpp中的构造函数实现。

内容的提问来源于stack exchange，提问作者Dustin Boatman