全局和局部函數和跨類變量。怎麼樣？我做對了嗎？

Question

當它應該小於零時，最終輸出爲12，我認爲這是因爲全局變量沒有被更改。我對嗎？我需要改變什麼？

central.cpp（主文件）

/* 
* central.cpp 
* 
* Created on: Feb 7, 2017 
*  Author: Harry Evans Allen, IV 
*/ 
#include <iostream> 
#include <string> 
#include "combatfunctions.h" 

using namespace std; 

int main(void){ 
    string name; 
    cout << "Hello, Welcome to Silver Stone.\nWhat is your name?\n"; 
    cin >> name; 
    combat_functions mainC(name, 15,5,3,3); 
    combat_functions Rick("Rick", 12,4,3,3); 
    mainC.playerFight(mainC,Rick); 
    cout << Rick.getHP(); 
} 

Rick.getHP（）應輸出的值0 < =但保持輸出12：原始值

combatfunctions.cpp

/* 
* combatfunctions.cpp 
* 
* Created on: Feb 7, 2017 
*  Author: ted 
*/ 

#include "combatfunctions.h" 
#include <iostream> 
#include <string> 

using namespace std; 
int health, attack, defense, movement; 
string name; 

combat_functions::combat_functions(string callsign, int hp, int power, int shield, int mobility){ 
    health=hp; 
    attack=power; 
    defense=shield; 
    movement=mobility; 
    name=callsign; 
} 
int combat_functions::getHP(){ 
    return health; 
} 
int combat_functions::getAttack(){ 
    return attack; 
} 
int combat_functions::getDefense(){ 
    return defense; 
} 
int combat_functions::getMobility(){ 
    return movement; 
} 
string combat_functions::getName(){ 
    return name; 
} 
void combat_functions::setHP(int increment){ 
    health+=increment; 
} 
void combat_functions::setAttack(int increment){ 
    attack+=increment; 
} 
void combat_functions::setDefense(int increment){ 
    defense+=increment; 
} 
void combat_functions::setMobility(int increment){ 
    movement+=increment; 
} 

bool combat_functions::isAlive(combat_functions player){ 
    if(player.getHP()>=1){ 
     return 1; 
    }else{ 
     return 0; 
    } 
} 

void combat_functions::playerFight(combat_functions player1, combat_functions player2){ //This functions lets the players take from eachother's value 
    while(isAlive(player1)&&isAlive(player2)){ 
     if(player2.getDefense()<player1.getAttack()){ 
      player2.setHP(-1*(player1.getAttack()-player2.getDefense())); //Should change the global value of hp 
     } 
     if(player1.getDefense()<player2.getAttack()){ 
      player1.setHP(-1*(player2.getAttack()-player1.getDefense())); //Should change the global value of hp 
     } 
     if(!isAlive(player1)){ 
      cout << player1.getName() << " has died."<<endl; 
     }else if(!isAlive(player2)){ 
      cout << player2.getName() << " has died."<<endl; 
     }else{ 
      cout << player1.getName() << " " << player1.getHP() << "\n" <<player2.getName() << " " << player2.getHP() << endl; 
     } 
    } 
} 

combatfunctions.h

/* 
* combatfunctions.h 
* 
* Created on: Feb 7, 2017 
*  Author: ted 
*/ 

#ifndef COMBATFUNCTIONS_H_ 
#define COMBATFUNCTIONS_H_ 
#include <string> 

using namespace std; 

class combat_functions { 
public: 
    combat_functions(string, int, int, int, int); 
    int getHP(); 
    int getAttack(); 
    int getDefense(); 
    int getMobility(); 
    string getName(); 
    void setHP(int); 
    void setAttack(int); 
    void setDefense(int); 
    void setMobility(int); 
    bool isAlive(combat_functions); 
    void playerFight(combat_functions, combat_functions); 
private: 
    int health, attack, defense, movement; 
    string name; 
}; 

#endif /* COMBATFUNCTIONS_H_ */ 

Answer 1

你傳入combat_functions爲值爲combat_functions::playerFight()，而應該把它作爲參考。

當您將參數作爲值傳遞時，將會生成一個變量副本。當您在函數中修改變量時，實際上您正在修改它的副本，而不是原始變量。

做正確的方法，是用參考而不是值：

void playerFight(combat_functions& player1, combat_functions& player2); 

或者使用指針：

void playerFight(combat_functions *player1, combat_functions *player2); 

你的代碼的另一件事，全局變量在定義爲combatfunctions.cpp似乎沒有必要。而playerFight()更改類中的變量，而不是全局變量。如果你真的想改變全局變量（雖然我不認爲這是你想要的），你應該使用::health,::attack ..來明確告訴編譯器。或者更好的方法，將全局變量的名稱更改爲g_health，g_attack。所以編譯器不會誤解。