类对象不会 push_back 到向量上

Posted 2023-02-21

【中文标题】类对象不会 push_back 到向量上

【英文标题】：Class object will not push_back onto vector

【发布时间】：2017-01-26 17:33:58

【问题描述】：

编译和除了添加“船”之外的所有内容

船的构造函数

Ship::Ship(std::string name, int length, std::string show) 

    std::string _name = name;
    int _length = length;
    std::string _show = show;
    

void Ships::buildShip() 
        std::string name, show;
        int length = 0;
        std::cout << "What is the name of the ship?  ";
        std::cin >> name;

        std::cout << "How long is the ship in feet?  ";
        std::cin >> length;

        std::cout << "What show/movie is the ship from?  ";
        std::cin >> show;
        std::cout << std::endl;
        Ship ship(name, length, show);
        addShip(ship);



void Ships::addShip(Ship &ship) 
    ships.push_back(ship);

我确定这很明显，我在网上搜索并没有发现任何有用的信息。如果需要其他任何内容，我只从我的代码中获取 sn-ps 让我知道。提前致谢！

    /Ship.h
#pragma once
#include <string>

class Ship 
    std::string _name;
    int _length;
    std::string _show;

public:
    Ship()
        std::string name = _name;
        int length = _length;
        std::string show = _show;
    ;
    Ship(std::string _name, int _length, std::string _show);
    std::string getName();
    int getLength();
    std::string getShow();

;

    /Ship.cpp
#include <string>
#include "Ship.h"

Ship::Ship(std::string name, int length, std::string show) 

    std::string _name = name;
    int _length = length;
    std::string _show = show;


std::string Ship::getName() 
    return _name;


int Ship::getLength() 
    return _length;


std::string Ship::getShow() 
    return _show;


    /Ships.h
#pragma once
#include <vector>
#include "Ship.h"

class Ships 
    std::vector<Ship> ships;
public:
    void addShip(Ship &ship);
    int getCount();
    Ship getLongestShip();
    void buildShip();
    int getNumberOfShipsLongerThan(int input);
    void displayShips();
;

    /Ships.cpp
#include "Ships.h"
#include <iostream>

void Ships::addShip(Ship &ship) 
    ships.push_back(ship);



int Ships::getCount() 
    return ships.size();


Ship Ships::getLongestShip() 
    Ship longestShip = ships[0];
    for (Ship aShip : ships) 
        if (longestShip.getLength() < aShip.getLength())
            longestShip = aShip;
    
    std::cout << "The longest ship is the " << longestShip.getName() << std::endl;
    std::cout << "From end to end the length is " << longestShip.getLength() << std::endl;
    std::cout << "The show/movie it is from is " << longestShip.getShow() << std::endl;
    return longestShip;


int Ships::getNumberOfShipsLongerThan(int input) 
    int longerThan = 0;
    int size = ships.size();
    for (int i = 0; i < size; i++) 
        if (input < ships[i].getLength())
            longerThan++;
    
    return longerThan;


void Ships::displayShips() 
    std::cout << " Complete Bay Manifest " << std::endl;
    std::cout << "***********************" << std::endl;
    for (int i = 0; i < ships.size(); i++) 
        int a = i + 1;
        std::cout << "Ship (" << a << ")" << std::endl;
        std::cout << "Name: " << ships[i].getName() << std::endl;
        std::cout << "Length: " << ships[i].getLength() << std::endl;
        std::cout << "Show: " << ships[i].getShow() << std::endl<<std::endl;
    


void Ships::buildShip() 
        std::string name, show;
        int length = 0;
        std::cout << "What is the name of the ship?  ";
        std::cin >> name;

        std::cout << "How long is the ship in feet?  ";
        std::cin >> length;

        std::cout << "What show/movie is the ship from?  ";
        std::cin >> show;
        std::cout << std::endl;
        Ship ship(name, length, show);
        addShip(ship);


    /driver.cpp
#include <iostream>
#include "Ship.h"
#include "Ships.h"

void menu();
Ship buildShip();
void shipsInBay(Ships &ships);
void processDirective(int choice, Ships &ships);
void longerThan(Ships &ships);

int main() 
    std::cout << "Welcome to Daniel Mikos' Ship Bay!" << std::endl << std::endl;
    menu();
    system("PAUSE");
    return 0;


void menu() 
    Ships ships;
    int choice = 0;
        std::cout << "Please make a selection" << std::endl;
        std::cout << " (1) Add a ship to the bay" << std::endl;
        std::cout << " (2) How many ships are already in the bay?" << std::endl;
        std::cout << " (3) Which ship is the longest? " << std::endl;
        std::cout << " (4) Ships longer than ___? " << std::endl;
        std::cout << " (5) Manifest of all ships currently logged" << std::endl;
        std::cout << " (6) Exit" << std::endl;
        std::cout << " Choice: ";
        std::cin >> choice;
        processDirective(choice, ships);


Ship buildShip() 
    std::string name, show;
    int length = 0;
    std::cout << "What is the name of the ship?  ";
    std::cin >> name;

    std::cout << "How long is the ship in feet?  ";
    std::cin >> length;

    std::cout << "What show/movie is the ship from?  ";
    std::cin >> show;
    std::cout << std::endl;
    Ship ship(name, length, show);
    return ship;


void shipsInBay(Ships &ships) 
    int count = ships.getCount();
    std::cout << std::endl;
    std::cout << "There is currently " << count;
    std::cout << " ship(s) in bay" << std::endl << std::endl;


void longerThan(Ships &ships) 
    int input = 0;
    std::cout << "Find ships longer than? ";
    std::cin >> input;
    std::cout << "There are " << ships.getNumberOfShipsLongerThan(input) << "longer than " << input << "feet";


void processDirective(int choice, Ships &ships) 
    if (choice == 1)
        buildShip();
    if (choice == 2)
        shipsInBay(ships);
    if (choice == 3)
        ships.getLongestShip();
    if (choice == 4)
        longerThan(ships);
    if (choice == 5)
        ships.displayShips();
    menu();

我所有的代码都有

【问题讨论】：

你怎么知道它没有添加到向量中？请提供minimal reproducible example。

尝试添加屏幕截图，但我有一个 ship.size(); （船是我的矢量）在我添加一个之后，我运行大小，它出现为 0。我之前运行过它，当我尝试显示它时它会说 1 buuut，名称和显示将为空白，而长度会是-803254

你的构造函数看起来不对。为什么要创建新的局部变量 _name、_length 和 _show 而不是初始化类成员？

@Mikos 没有 minimal reproducible example 我们可以自己运行我们不知道您如何确定您的代码不起作用。也就是说，drescherjm 是正确的，Ship 的构造函数是错误的。您正在为我只能假设应该是数据成员的内容创建局部变量。

Ships 应该是一个“包装”类。构造函数就是这样，所以我可以访问 Ship 的私有成员

【参考方案1】：

要将对象添加到对象向量中，请使用 emplace_back() 并将构造函数参数作为参数传递给 emplace。然后它将在适当位置构建对象，因此调用：

ships.emplace_back(name, length, show);

在适当的位置构建您的船对象。正如@Kevin 所指出的，您的构造函数也不正确。您需要将其更改为：

this->_name = name;
this->_length = length;
this->_show = show;

假设我猜对了你的班级设计。

编辑

试图从中构建一个最小示例，这对我来说很好：

Header.h

class Ship 
    std::string _name;
    int _length;
    std::string _show;

public:
    Ship();
    Ship(std::string _name, int _length, std::string _show);
    std::string getName();
    int getLength();
    std::string getShow();

;

class Ships 
public:

    void addShip(Ship &ship);
    void buildShip();

    std::vector<Ship> ships;
;

和Source.cpp

#include "Header.h"

Ship::Ship(std::string name, int length, std::string show) 

    this->_name = name;
    this->_length = length;
    this->_show = show;


void Ships::buildShip() 
std::string name = "Name";
std::string show = "Show";
int length = 0;
ships.emplace_back(name, length, show);



int main(int argc, char argv[])

    Ships ships;
    ships.buildShip();

    std::cout << "Number of ships = " << ships.ships.size() << std::endl;
    return 0;

打印Number of ships = 1。你能把它瘦成这样吗？

【讨论】：

这与问题无关。 Ship ship(...); ships.push_back(ship); 应该等同于 ships.emplace_back(...);。也应该使用初始化列表而不是this->__ = __;。

好建议，但这并不能解决问题。我们需要 OP 提供一个 mcve 来给出真正的答案

公平的cmets，我刚刚看到了刚才发布的其余代码，所以会再看一下。

@CodingLumis 谢谢你的帮助，我已经按照你上面写的那样做了所有的改变。仍然无法正常工作...我会继续尝试

仍然无法正常工作 我建议您学习使用调试器逐行执行代码。这样你就可以看到你的代码没有像你期望的那样运行的确切点。