c++ - 搜索功能不起作用

Question

这是我的代码。这是家庭作业，但我已经全部完成了。但是搜索功能不起作用。我知道我做错了什么。用户必须输入名称才能搜索，它应该会显示整个条目。 void 搜索函数出现错误，显示“error C2120: 'void' illegal with all types”

            // Awholenew world.cpp : Defines the entry point for the console application.
            //

            #include "stdafx.h"
            #include<process.h>
            #include<iomanip>
            #include<stdio.h>
            #include<string.h>
            #include<fstream>
            #include<sstream>
            #include<iostream>
            #include<conio.h>
            #include<stdlib.h>

            using namespace std;

            struct main
            {
                char FName[20];
                char Last[20];
                char Address[30];
                long Phone;
                int ID;
                long CNIC;
            }obj;

            class Main
            {

            public:
                virtual void init()
                {
                    cin.getline(obj.FName,20);
                    cout << "Enter Name: ";
                    cin.getline(obj.Last,20);

                    cout << "Enter Address: ";
                    cin.getline(obj.Address, 30);
                    cout << "Enter Phone: ";
                    cin>>obj.Phone; 

                }
                void view()
                {
                    cout << "Name: " << obj.Last<< endl;
                    cout << "Address: " << obj.Address << endl;
                    cout << "Phone: " << obj.Phone << endl;
                    cout << "CNIC: " << obj.CNIC << endl;
                    cout << "ID: " << obj.ID << endl;

                }




                virtual void search()
                {
                    char choice4;   
                    char Target[20];
                    int Found=0;

                    fstream fin;
                    if (fin.open("Main.txt", ios::in| ios::out) == NULL)
                        cout<<"File is empty" << endl;
                    else
                        cout<<"Enter Name: " << endl;
                    cin.getline(Target, 20);

                    while(!fin.eof() && Found ==0)
                    {
                        fin<< endl << obj.Last << endl <<obj.Address <<endl <<obj.Phone << endl << obj.CNIC << endl << obj.ID;
                        if (strcmp(Target, obj.Last) == 0)
                            Found =1;
                    }
                    if(Found)
                    {
                        Main::view();

                    }
                    else if (!Found)
                        printf("**There is no such Entry**\n");
                    fin.close();

                }



                void display()
                {

                    char BUFFER[100];
                    ifstream fin("Main.txt");


                        while (!fin.eof())
                        {
                        fin.getline(BUFFER, 100);
                        cout << BUFFER << endl;

                        }
                }

            };

            class Teacher : public Main
            {
            public:

            void tinit()
            {
                ofstream fin("Main.txt", ios::app);
                Main::init();
                cout << "Enter CNIC of Teacher" << endl;
                cin>>obj.CNIC;
                fin<< endl << obj.Last << endl << obj.Address << endl << obj.Phone << endl << "Teacher CNIC: " << obj.CNIC << endl;

            }

            };

            class Student : public Main
            {
            public:
                void sinit()
                {
                ofstream fin("Main.txt", ios::app);
                Main::init();
                cout << "Enter ID of Student" << endl;
                cin>>obj.Phone; 
                fin<< endl << obj.Last <<endl << obj.Address << endl  << obj.Phone << endl  << "Student ID" << obj.ID << endl;
                }

            };

            class Employee : public Main
            {
            public:
                void einit()
                {

                ofstream fin("Main.txt", ios::app);
                Main::init();
                cout << "Enter Employee CNIC" << endl;
                cin>>obj.CNIC;  
                fin << endl << obj.Last <<endl  << obj.Address << endl  << obj.Phone << endl << "Employee CNIC: " << obj.CNIC << endl;
                }

            };
            int _tmain(int argc, _TCHAR* argv[])
            {
                Main* myarr[100];
                Teacher* tearr[100];
                Student* starr[100];
                Employee* emarr[100];
                int var=0;
                int choice;
                char input;

                start:
                printf("===============MAIN MENU===============");
                printf("\n[1]Insert\n[2]Display All\n[3]Search\n[4]Exit\n");
                printf("=======================================");
                printf("\n\nEnter Your Choice: ");

                cin >> choice;

                switch(choice)
                {

                case 1:
            label:
                    cout<< "Enter Choice s/t/e" << endl;
                    cin >> input;


                if (input == 't')
                    tearr[var]->tinit();
                if (input == 's')
                    starr[var]->sinit();
                if (input == 'e')
                    emarr[var]->einit();

                cout << " Enter another (y/n)? ";
                cin >> input;

                if (input == 'y')
                    goto label;
                else 
                    goto start;
                    break;
                case 2:
                        myarr[var]->display();
                        break;
                case 3:
                    myarr[var]->search();
                    break;
                case 4:
                    cout << "Are you sure? y/n" << endl;
                    char in;
                    cin>>in;
                    if (in=='y')
                        getch();
                    else goto start;
                    break;
                default:
                    return 0;
                    break;

                return 0;
                }
            }

Answer 1

我能看到的一个问题是:

fstream fin;
if (fin.open("Main.txt", ios::in| ios::out) == NULL)

函数 fstream::open 声明为:

void open ( const char * filename, 
            ios_base:openmode mode = ios_base::in | ios_base::out );

如您所见，它的返回类型是 void，因此您不能在 if 表达式中使用它。