在 for 循环中填充后向量大小 returns 0

Question

我一直在开发一个小型 C++ 应用程序，该应用程序与讲师和学生根据 class 他们 teach/take 匹配在一起。

每个讲师都有一个学生向量。当一名学生与讲师教授的课程相同 class 时，我们会将同一名学生添加到同一位讲师。

我有 2 个 for 循环遍历所有讲师和学生，然后比较两者的 classes，如果它们匹配，则将该学生添加到讲师。

循环后，我遍历所有讲师并获取每个讲师的大小。但是 returns 返回 0，它应该返回 1。（因为一个学生匹配每个讲师的 class）。

Lecturer.h

#pragma once
#include <iostream>
#include "Person.h"
#include "Student.h"
#include <vector>
#include <string>

using namespace std;

class Lecturer : public Person {

public:
    // Lecturer(string department, string specialization, string name, int age, char gender)
    //     : department(department), specialization(specialization), name(name), age(age), gender(gender) {}

    Lecturer() { }

    Lecturer(string department, string specialization, string name, int age, char gender, string uniClass){
        this->department = department;
        this->specialization =specialization;
        this->name = name;
        this->age = age;
        this->gender = gender;
        this->uniClass = uniClass;
    }

    // Class Methods
    void addStudent(Student student);

    // Setter Methods
    void setDepartment(string dprt);
    void setSpecialization(string splz);
    void setName(string nme);
    void setAge(int ag);
    void setGender(char g);

    // Getter Methods
    string getDepartment();
    string getSpecialization();
    string getUniClass();

    int getStudentsSize();
    vector<Student> getStudents();

private:
    string department;
    string specialization;
    vector<Student> students;
    string uniClass;
};

void Lecturer::addStudent(Student student)
{
    cout << student.getName() << endl;
    students.push_back(student);
}

int Lecturer::getStudentsSize()
{
    return students.size();
}

Student.h

#pragma once
#include <iostream>
#include "Person.h"
#include <string>

using namespace std;

class Student : public Person {

public:
    // Student(string major, string minor, int id, string name, int age, char gender)
    //     : major(major), minor(minor), id(id), name(name), age(age), gender(gender) {}

    Student() { }

    Student(string major, string minor, int id, string name, int age, char gender, string uniClass){
        this->major = major;
        this->minor = minor;
        this->id = id;
        this->name = name;
        this->age = age;
        this->gender = gender;
        this->uniClass = uniClass;
    }
    // Setter Methods
    void setMajor(string mjr);
    void setMinor(string mnr);
    void setId(int _id);
    void setName(string nme);
    void setAge(int ag);
    void setGender(char g);

    // Getter Methods
    string getMajor();
    string getMinor();
    int getId();
    string getUniClass();
    string getName();

private:
    string major;
    string minor;
    int id;
    string uniClass;
};

string Student::getUniClass()
{
    return uniClass;
}

main.cpp

#include <iostream>
#include <string>
#include "Person.h"
#include "Lecturer.h"
#include "Student.h"

int main()
{

    vector<Lecturer> lecturers;
    lecturers.push_back(Lecturer("Computing", "Advanced Programming", "John", 40, 'm', "AB101"));
    lecturers.push_back(Lecturer("Business", "Finance", "Dave", 42, 'm', "AB102"));
    lecturers.push_back(Lecturer("Science", "Physics", "Bill", 46, 'm', "AB103"));

    vector<Student> students;
    students.push_back(Student("Computer Science", "Maths", 123, "Mike", 20, 'm', "AB101"));
    students.push_back(Student("Business", "Economics", 142, "Jane", 21, 'f', "AB102"));
    students.push_back(Student("Engineering", "Physics", 151, "Mary", 19, 'f', "AB103"));

    for(Lecturer lecturer : lecturers)
    {
        for(Student student : students)
        {
        //cout << "Name: " << student.getUniClass() << endl;
        if (lecturer.getUniClass().compare(student.getUniClass()) == 0)
            {
                // ADDING A STUDENT THAT MATCHES THE CLASS
                lecturer.addStudent(student);
            }
        }
    }

    for(Lecturer lecturer : lecturers)
    {
        // EACH LECTURER'S STUDENTS SIZE IS 0 HERE (SHOULD BE 1)
        cout << lecturer.getStudentsSize() << endl;
    }
}

Answer 1

您到处都在使用价值观。这意味着副本。

您的第一个更改是使用 references 进行迭代。例如：

for (Lecturer& lecturer : lecturers)
//           ^

Answer 2

其他不涉及最终是您的实际错误的注释：

Each Lecturer has a vector of students.

为什么？每个讲师应该有一个（n 无序）set 个学生。学生不会同时存在多次。此外，它们没有固有的相关顺序。实际上，讲师们所教授的每一门课程都需要这样一套。

此外，您为什么假设每个学生只选了一个 class？ (看源码)啊！现在我懂了。

你的"students"不是学生，真的是学生的课业记录
您的"lecturers"不是讲师，它们是带有讲师信息的课程记录。

非常混乱。请解决这个问题。如果您使用适当的 terms/names 和适当的数据结构，您很可能会自己找出错误。

I have 2 for loops that loop through all lecturers and students and then compares the classes of both and if they match, add that student to the lecturer.

两个循环？在这种情况下，你自己写它们太深了——就像你在重新发明轮子一样！用 std::copy_if 的调用替换内部循环。这也可能有助于找到错误。

在 for 循环中填充后向量大小 returns 0

Vector size returns 0 after being populated in a for loop

c++

c++11

vector

stdvector

c++-standard-library