尝试使用 init() 启动我的程序，但它告诉我没有合适的默认构造函数可用

Question

我正在尝试使用 init() 来启动我的程序，但它告诉我 main.cpp 的这一行 MerkelMain app{}; “没有合适的默认构造函数可用”。我需要添加什么才能使其正常工作？我缺少构造函数吗？

main.cpp

#include "OrderEntry.h"
#include "MerkelMain.h"
#include "CSVReader.h"

int main()
{
    MerkelMain app{};
    app.init();
}

MerkelMain.cpp

#include <iostream>
#include <vector>
#include "OrderEntry.h"
#include "MerkelMain.h"
#include "OrderFood.h"

MerkelMain::MerkelMain(OrderFood _orders)
: orders (_orders)
{

}

void MerkelMain::init()
{
    std::string input;

    while (true)
    {
        printMenu();    
        input = getUserOption();
        processUserOption(input);
    }
}

void MerkelMain::printMenu()
{
    std::cout << "Welcome to Restaurant Firebird" << std::endl;
    std::cout << "a . Order a plate of chicken rice" << std::endl;
    std::cout << "b . Order a plat for wanton noodles" << std::endl;
    std::cout << "c . Order a cup of Coffee" << std::endl;
    std::cout << "d . Order a cup of Tea" << std::endl;
    std::cout << "e . Repeat Order" << std::endl;
    std::cout << "f . Exit Menu" << std::endl;
    std::cout << "------------------------------------" << std::endl;
    std::cout << "Type an option from a-f" << std::endl;
}


std::string MerkelMain::getUserOption()
{
    std::string choice;
    std::cin >> choice;
    return choice;
}

int MerkelMain::getQuantity()
{
    int qty;
    std::cin >> qty;
    return qty;
}

void MerkelMain::processUserOption(std::string choice)
{
   std::endl(std::cout);

   if (choice == "a")
    {
        std::cout << "How many plates of chicken rice would you like to order?" << std::endl;
        OrderType order = OrderType::chickenrice;
        int qty = getQuantity();
        std::endl(std::cout);
        std::cout << "Thank you for your order of " << qty << " plates of Chicken Rice." << std::endl;
        std::endl(std::cout);
        OrderEntry food_order = OrderEntry(qty, order);
        orders.orderQueue.push_back(std::move(food_order));
    }
    if (choice == "b")
    {
        std::cout << "How many plates of wanton noodles would you like to order?" << std::endl;
        OrderType order = OrderType::wantonnoodle;
        int qty = getQuantity();
        std::endl(std::cout);
        std::cout << "Thank you for your order of " << qty << " plates of Wanton Noodles." << std::endl;
        std::endl(std::cout);
        OrderEntry food_order = OrderEntry(qty, order);
        orders.orderQueue.push_back(std::move(food_order));
    }
    if (choice == "c")
    {
        std::cout << "How many cups of Coffee would you like to order?" << std::endl;
        OrderType order = OrderType::coffee;
        int qty = getQuantity();
        std::endl(std::cout);
        std::cout << "Thank you for your order of " << qty << " cups of Coffee." << std::endl;
        OrderEntry food_order = OrderEntry(qty, order);
        orders.orderQueue.push_back(std::move(food_order));
    }
    if (choice == "d")
    {
        std::cout << "How many cups of Tea would you like to order?" << std::endl;
        OrderType order = OrderType::tea;
        int qty = getQuantity();
        std::endl(std::cout);
        std::cout << "Thank you for your order of " << qty << " cups of Tea." << std::endl;
        std::endl(std::cout);
        OrderEntry food_order = OrderEntry(qty, order);
        orders.orderQueue.push_back(std::move(food_order));
    }
    if (choice == "e")
    {
        std::cout << "You have ordered: " << std::endl;

        for (unsigned int i = 0; i < orders.orderQueue.size(); ++i)
        {
            std::cout << orders.orderQueue[i].qty << " " << OrderEntry::orderTypeToString(orders.orderQueue[i].orderType) << std::endl;
        }
        std::endl(std::cout);
    }
    if (choice == "f")
    {
        std::cout << "Thank you and see you again soon." << std::endl;
        
    }
}

MerkelMain.h

#pragma once
#include <iostream>
#include <vector>
#include "CSVReader.h"
#include "OrderEntry.h"
#include "OrderFood.h"

class MerkelMain
{
    public:
        MerkelMain(OrderFood _orders);
        void init();
    private:
        void printMenu();
        std::string getUserOption();
        int getQuantity();
        void processUserOption(std::string choice);

        OrderFood orders;
        OrderFood orderFood{"Rest_Order.csv"};
};

Answer 1

在您的 main 函数中，您试图通过调用其默认构造函数来实例化 MerkelMain 的实例。

MerkelMain app{};

但是，由于您有一个用户定义的构造函数MerkelMain(OrderFood _orders)，编译器将不再自动生成默认构造函数。

为了使其工作，您需要手动定义默认构造函数或在实例化 MerkelMain.

时传递 OrderFood 的实例

Answer 2

您在执行 MerkelMain app{}; 时试图使用默认构造函数，但是您的 MerkelMain class 没有默认构造函数。

一种可能的方法是添加一个默认构造函数，该构造函数委托给您当前的转换构造函数以从看起来像默认csv文件的内容中读取。

.hpp

class MerkelMain
{
    public:
        MerkelMain();                    // added default constructor
        MerkelMain(OrderFood _orders);   // leave your current converting ctor as-is
        void init();
    private:
        void printMenu();
        std::string getUserOption();
        int getQuantity();
        void processUserOption(std::string choice);

        OrderFood orders;
        OrderFood orderFood{"Rest_Order.csv"}; // this should probably be removed
};

.cpp

// add this without changing the current converting constructor:
MerkelMain::MerkelMain() :
    MerkelMain(OrderFood{"Rest_Order.csv"}) // delegate to the converting constructor
{}

尝试使用 init() 启动我的程序，但它告诉我没有合适的默认构造函数可用

Trying to use init() to start my program but it tells me no appropriate default constructor available

c++

constructor

init