Question

我正在尝试制作一个Question对象。 Question是班级，但我收到的错误是：

错误1错误C2440：'初始化'：无法从Questions *转换为Questions

我正在尝试创建一个对象，因此我可以将其放入multimap类型的<int, Questions>

这是我的代码：

#include <iostream>
#include "Questions.h"
using namespace std;

Questions::Questions() {}
Questions::Questions(string question,string correctAnswer, string wrongAnswer1,string wrongAnswer2,string wrongAnswer3) {}

void Questions::questionStore() {
    Questions q1 = new Questions("Whats the oldest known city in the world?", "Sparta", "Tripoli", "Rome", "Demascus");
    string q2 = ("What sport in the olympics are beards dissallowed?", "Judo", "Table Tennis", "Volleyball", "Boxing");
    string q3 = ("What does an entomologist study?", "People", "Rocks", "Plants", "Insects");
    string q4 = ("Where would a cowboy wear his chaps?", "Hat", "Feet", "Arms", "Legs");
    string q5 = ("which of these zodiac signs is represented as an animal that does not grow horns?", "Aries", "Tauris", "Capricorn", "Aquarius");
    string q6 = ("Former Prime Minister Tony Blair was born in which country?", "Northern Ireland", "Wales", "England", "Scotland");
    string q7 = ("Duffle coats are named after a town in which country?", "Austria", "Holland", "Germany", "Belgium");
    string q8 = ("The young of which creature is known as a squab?", "Horse", "Squid", "Octopus", "Pigeon");
    string q9 = ("The main character in the 2000 movie ""Gladiator"" fights what animal in the arena?", "Panther", "Leopard", "Lion", "Tiger");

    map.insert(pair <int, Questions>(1, q1));
    map.insert(pair <int, string>(2, q2));
    // map.insert(pair<int,string>(3, q3));
    for (multimap <int, string, std::less <int> >::const_iterator iter = map.begin(); iter != map.end(); ++iter)
        cout << iter->first << '\t' << iter->second << '\n';
}

Answer 1

new表达式为您提供指向您动态分配的对象的指针。你需要做Questions* q1 = new Questions(...);。但是，如果您不需要动态分配（最终将对象复制到地图中），请不要打扰。只需Questions q1(...);。

据推测，您将更改以下行（q2，q3等）以匹配，但因为它们不符合您的预期。 (..., ..., ...)将评估为此逗号分隔列表中最右侧的项目。因此，您的q2行等同于string q2 = "Boxing";。

Answer 2

Questions q1 = new Questions语法不正确。

从map.insert(pair <int, Questions>(1, q1));我可以看到你的map值类型是Questions对象而不是Questions指针，所以它应该是

Questions q1 = Questions ("Whats the oldest known city in the world?", "Sparta" , "Tripoli" , "Rome", "Demascus");

此外，您的变量映射与std :: map具有相同的名称，这是一个STL容器，建议您使用其他名称，例如：question_map;

修改

要允许<< iter->second，您需要为问题类型重载operator<<。

std::ostream& operator<<(const std::ostream& out, const Questions& q) { out << q.question; // I made up this member as I can't see your Questions code return out; }

Answer 3

questionScore方法的第一行是问题：

Questions q1 = new Questions ...

new x返回指向x对象的指针，因此应将q1定义为指针。

Questions * q1 = new Questions ...

尝试制作对象时出错

3 个答案: