c++ - c++中如何调用不同类的函数？

Question

我有两个类，Apple 和 Banana。我想用函数 callItestA 更改 Banana 类中 iTestA(Apple 类)的值。我尝试使用指针，但它似乎没有用(值没有改变)...

这是我的 Banana.cpp

#include "Banana.h"
#include <iostream>
#include <fstream>

using namespace std;

//Konstruktor
Banana::Banana()
{
    cout << "i'm a banana" << endl;
}

//Destruktor
Banana::~Banana()
{
}

//write test
void Banana::writeBanana(){
    ofstream myfile;
    myfile.open("banana.txt", fstream::in | fstream::out | fstream::app);
    myfile << "more bananas\n";
    myfile.close();
}

void Banana::callIsetA(Apple a){
    //set iTestA in class Apple to 2
    a.setItestA(2);
}

和 Apple.cpp

#include "Apple.h"
#include <iostream>
#include <istream>
#include <fstream>

using namespace std;

int itestA = 0;

//Konstruktor
Apple::Apple()
{
    cout << "i'm an apple" << endl;
}

//Destruktor
Apple::~Apple()
{
}

//write test
void Apple::writeApple()
{
    ofstream myfile;
    myfile.open("apple.txt", fstream::in | fstream::out | fstream::app);
    myfile << itestA;
    //myfile << "more apples\n";
    myfile.close();
}

void Apple::setItestA(int i)
{
    itestA = i;
}

我希望你能帮助我!

编辑:我的香蕉.h

#ifndef BANANA_H
#define BANANA_H

class Apple;

class Banana
{
public:
    Banana();
    ~Banana();
    void writeBanana();
    void callIsetA(Apple);
};

#endif

和Apple.h

#ifndef APPLE_H
#define APPLE_H

class Banana;

class Apple
{
public:
    Apple();
    ~Apple();
    void writeApple();
    void setItestA(int i);
private:
    int itestA;
};

#endif

Answer 1

问题是您将 Apple 实例的拷贝传递给函数。所以这段代码改变了复制对象的值。

void Banana::callIsetA(Apple a){ //here is the definition of argument copy, next code will change it but not the object that was passed in to the function as initial argument
    //set iTestA in class Apple to 2
    a.setItestA(2); 
}

要更改原始对象的值，您需要传递其引用。这可能看起来像这样:

void Banana::callIsetA(Apple& a){
    //set iTestA in class Apple to 2
    a.setItestA(2);
}