‘'Vehicle’不是参数'_Ty‘的有效模板类型参数

Question

VS总是给我一个类项目的每个函数的标题中提到的错误(至少是Vehicle.h中的所有函数)，而且无论我多么努力，我都找不出它。这似乎不是由于任何循环定义，但也许答案很简单。该项目应该基于四个文件(两个头文件和两个..cpp文件)；我将在下面附加它们。

车辆h：

    #include <iostream>
    #include <fstream>
    #include <string>
    #include<vector>
    using namespace std;
    //Declaring Dealer class
    class Dealer
    {
    public:
        Dealer();
        int getDealerNum();
        void setDealerNum(int dealerNumber);
    private:
        int dealerNumber;
        Dealer *dealer;
    };

//Declaring Vehicle class
class Vehicle
{
public:
    Dealer *dealerType;
    Vehicle(string VIN, string make, string model, int year, double price);
    Vehicle();
    string getVIN();
    string getMake();
    string getModel();
    int getYear();
    double getPrice();
    void setVIN(string VIN);
    void setMake(string make);
    void setModel(string model);
    void setYear(int year);
    void setPrice(double price);
    friend Vehicle;
private:
    string VIN;
    string make;
    string model;
    int year;
    double price;
};

H(只包含一个函数，以节省一些空间)：

#include <iostream>
#include <fstream>
#include <stdlib.h>
#include<string>
#include<vector>
using namespace std;

//Declaring name for input and output file
ofstream outfile;
ifstream infile;

void displayInventory(vector<Vehicle>& vehicles)
{
    int i = 0;
    char query = 'a';
    int j = vehicles.size();
    //Simple loop to display the inventory, with a pause function to wait     for user exit
    while (query != 'x'&&query!='X')
    {
        for (i; i < j; i++)
        {
            cout << "Vehicle #" << i + 1 << endl;
            cout << "Vin: " << vehicles[i].getVIN << endl;
            cout << "Make: " << vehicles[i].getMake << endl;
            cout << "Model: " << vehicles[i].getModel << endl;
            cout << "Year: " << vehicles[i].getYear << endl;
            cout << "Price: $" << vehicles[i].getPrice << endl << endl;
        }
        cout << endl << "Enter 'x' to return to main menu" << endl;
        cin >> query;
        cout << endl;
        }
    }

Main.cpp：

#include <iostream>
#include <fstream>
#include <string>
#include<vector>
#include "Thomas-PA3 Functions.h"
#include "Thomas-PA3 Vehicle.h"
using namespace std;

void displayInventory(vector<Vehicle>& vehicles);
void addInventory(vector<Vehicle>& vehicles);
void deleteInventory(vector<Vehicle>& vehicles);
void updateInventory(vector<Vehicle>& vehicles);
void sortInventory(vector<Vehicle>& vehicles);
void searchInventory(vector<Vehicle>& vehicles);
void writeInventory(vector<Vehicle>& vehicles);
void refreshInventory(vector<Vehicle>& vehicles);

int main()
{
    char menu='0';
    vector<Dealer>dealers;
    vector<Vehicle>vehicles;

    while(menu!='8')
    {
    cout << "Welcome to the vehicle management menu." << endl;
    cout << "Please select an option from the following list:" << endl;
    cout << "1: Display vehicles" << endl;
    cout << "2: Add a vehicle" << endl;
    cout << "3: Update a vehicle" << endl;
    cout << "4: Delete a vehicle" << endl;
    cout << "5: Sort inventory by VIN" << endl;
    cout << "6: Search inventory by Make" << endl;
    cout << "7: Read inventory from file (will overwrite any changes)" << endl;
    cout << "8: Write inventory to file and exit" << endl;
    cin >> menu;
        switch(menu)
        {
        // Call to appropriate functions based upon user decision
        case '1': displayInventory(vehicles);
            break;
        case '2': addInventory(vehicles);
            break;
        case '3': updateInventory(vehicles);
            sortInventory(vehicles);
            break;
        case '4': deleteInventory(vehicles);
            break;
        case '5': sortInventory(vehicles);
            break;
        case '6': searchInventory(vehicles);
            break;
        case '7': refreshInventory(vehicles);
            break;
        case '8': sortInventory(vehicles);
            writeInventory(vehicles);
            break;
        //Error/incorrect input checking
        default: cout << endl << "Please make a valid selection" << endl << endl;
        }
    }
return 0;
}

Vehicle.cpp：

#include <iostream>
#include <fstream>
#include <string>
#include<vector>
#include "Thomas-PA3 Vehicle.h"
#include "Thomas-PA3 Functions.h"
using namespace std;
//Default constructor for Dealer
Dealer::Dealer()
{
    dealerNumber = 0;
}
//Function to get dealer number
int Dealer::getDealerNum()
{
return dealerNumber;
}

void Dealer::setDealerNum(int dealerNumber)
{
    cout << "Please input the new dealer number" << endl;
    cin >> dealerNumber;
}
//Custom constructor for Vehicle
Vehicle::Vehicle(string VIN, string make, string model, int year, double price)
{
    cout << "Vehicle data is initialized" << endl;
}
//Default constructor for Vehicle
Vehicle::Vehicle()
{
    VIN = "0";
    make = "";
    model = "";
    year = 0;
    price = 0;
}
//Functions to return member variables
string Vehicle::getVIN()
{
    return VIN;
}

string Vehicle::getMake()
{
    return make;
}

string Vehicle::getModel()
{
    return model;
}

int Vehicle::getYear()
{
    return year;
}

double Vehicle::getPrice()
{
    return price;
}
//Functions to set member variables
void Vehicle::setVIN(string VIN)
{
    cout << "Please input the vehicle's VIN #" << endl;
    cin >> VIN;
}

void Vehicle::setMake(string make)
{
    cout << "Please input the vehicle's make" << endl;
    cin >> VIN;
}

void Vehicle::setModel(string model)
{
    cout << "Please input the vehicle's model" << endl;
    cin >> VIN;
}

void Vehicle::setYear(int year)
{
    cout << "Please input the vehicle's year" << endl;
    cin >> VIN;
}

void Vehicle::setPrice(double price)
{
    cout << "Please input the vehicle's price" << endl;
    cin >> VIN;
}

Answer 1

在"Vehicles.h“之前包括"Functions.h”。因此，当编译器看到vector<Vehicle>时，它还不知道以后Vehicle将被定义为一个类。

C++分三个阶段编译。首先，预处理程序运行并执行#include语句等。这在每个.cpp文件中完成一次，并将结果提供给真正的编译器。然后编译器逐行编译此结果。最后，链接器将所有的东西粘合在一起。

这里的重要阶段是中间阶段。因为每个.cpp文件都是自上而下独立编译的，所以您可以将必要的头放在顶部。如果一个头需要另一个，你就把一个放在另一个上面。为了简化这一点，可以在另一个头中使用#include。毕竟，所有的#include语句都是执行的。最终，一切都会在.cpp文件中结束。

最后一点:您通常需要保护自己不受双重#include的影响。

#ifndef VEHICLE_H
#define VEHICLE_H

// Real contents of Vehicle.h go here, including any other #include statement

#endif

如果你现在写

#include "vehicle.h"
//.. other stuff
#include "vehicle.h"

预处理器将看到第二个语句，并注意已经定义了VEHICLE_H，因此不需要第二个包含。拼写注意:为了防止与class Vehicle和其他类似名称混淆，您不能在那里使用.，所以后缀是_H。