似乎无法通过调用代理类中的for循环从主目录中打印字符串数组(agents.cpp)。

Question

我试着打印数组到屏幕上。不幸的是，它打印了4行空白行。

// CarWarhouse.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

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

#include "agents.h"

using namespace std;

int main()
{
    string agentName;
    int agentID;

    agents A_1;

    cout << "Administrative login: ";
    cin >> agentName;
    A_1.setAgentName(agentName);
    cout << "Administrative password: ";
    cin >> agentID;

    while (agentID != A_1.getAgentID())
    {
        cout << "Invalid login\n";

        cout << "\nAdministrative password: ";
        cin >> agentID;
    }

    cout << endl << "Welcome back, Agent " << endl;

    cout << "Active Agents: " << endl;

    A_1.agentIdentities(); //Function call to agents.cpp

}

agents.cpp

#include "pch.h"
#include "agents.h"
#include <string>

agents::agents() {
    agentName = "";
    agentID = 1111;
    int const size = 4;
    string agentMembers[size] = { "Jacob", "Nathan", "Tomas", "Jack" }; //Agent members string array I want to print to screen.
}

agents::agents(string name, int ID)
{
    agentName = name;
    agentID = ID;
}

agents::~agents()
{}


string agents::getAgentName() const
{
    return  agentName;
}

int agents::getAgentID() const
{
    return agentID;
}

void agents::setAgentName(string incoming)
{
    agentName = incoming;
}

void agents::setAgentIdentity(int ID)
{
    agentID = ID;
}

void agents::agentIdentities() //Main calls this function.
{
    for (int i = 0; i < size; i++)
    {
        cout << agentMembers[i] << endl;
    }

    cout << agentMembers[0];
}


#pragma once

#include <iostream>
#include <string>

using namespace std;

#ifndef agents_h
#define agents_h

class agents{

public:
    //First thing, default constructor
    agents();

    //Overload Constructor
    agents(string, int);

    //Destructor

    ~agents();

    //Accessor Functions

    //If accessor doesn't modify member variables, end with const on the function name.

    string getAgentName() const;
        //getName returns name of the customer.

    int getAgentID() const;


    void setAgentName(string);
    //getName returns the newly assigned customer reference number.

    void setAgentIdentity(int);

    void agentIdentities();
    //Retrieves agent identites (names within the string array).

private:
    //Member variables
    string agentName;
    int agentID;
    string agentMembers[4];
    int size = 4;
};

#endif

我已经在代码中确定了关键感兴趣的三个领域。我尝试使用从main到agents.cpp的函数调用从main打印字符串数组。

每次我运行这段代码时，它都会打印4行空白行，我对c++相当陌生，因为这是我在大学的第四个星期。

谢谢。

Answer 1

这是错误(非常常见的新手错误)。

agents::agents() {
    agentName = "";
    agentID = 1111;
    int const size = 4;
    string agentMembers[size] = { "Jacob", "Nathan", "Tomas", "Jack" }; 
}

它应该是

agents::agents() {
    agentName = "";
    agentID = 1111;
    size = 4;
    agentMembers = { "Jacob", "Nathan", "Tomas", "Jack" }; 
}

您的代码声明了名为size和agentMembers的新变量，它们与类中声明的变量完全无关(除了具有相同的名称)。这就是为什么构造函数不更新类变量的原因，因为所设置的只是一些局部变量，一旦构造函数退出，这些局部变量就不再存在。

但是，由于我们在构造函数的顶部，因此值得指出的是，初始化类变量的最佳方法是使用initialiser列表

agents::agents() : agentName(""), agentID(1111), size(4),
    agentMembers{ "Jacob", "Nathan", "Tomas", "Jack"} {
}

这个版本用给定的值初始化类变量，您的版本有两个步骤，首先默认初始化类变量，然后将给定的值分配给变量。这是低效率和没有理由不喜欢初始化列表版本。