Question

我正在尝试在我创建的UserLogin类上重载输入操作符。不会抛出编译时错误，但也不会设置值。

一切都在运行，但是ul的内容仍然存在：字符串id是莎莉登录时间是00:00 时间注销是00:00

入口点

#include <iostream>
#include "UserLogin.h"

using namespace std;

int main() {
    UserLogin ul;

    cout << ul << endl; // xxx 00:00 00:00
    cin >> ul; // sally 23:56 00:02
    cout << ul << endl; // Should show sally 23:56 00:02
                        // Instead, it shows xxx 00:00 00:00 again

    cout << endl;
    system("PAUSE");
}

UserLogin.h

#include <iostream>
#include <string>
#include "Time.h"

using namespace std;

class UserLogin
{
    // Operator Overloaders
    friend ostream &operator <<(ostream &output, const UserLogin user);
    friend istream &operator >>(istream &input, const UserLogin &user);

    private:
        // Private Data Members
        Time login, logout;
        string id;

    public:
        // Public Method Prototypes
        UserLogin() : id("xxx") {};
        UserLogin( string id, Time login, Time logout ) : id(id), login(login), logout(logout) {};
};

UserLogin.cpp

#include "UserLogin.h"

ostream &operator <<( ostream &output, const UserLogin user )
{
    output << setfill(' ');
    output << setw(15) << left << user.id << user.login << " " << user.logout;

    return output;
}

istream &operator >>( istream &input, const UserLogin &user )
{
    input >> ( string ) user.id;
    input >> ( Time ) user.login;
    input >> ( Time ) user.logout;

    return input;
}

Answer 1

您对operator>>的定义是错误的。你需要通过非const引用传递user参数，并摆脱强制转换：

istream &operator >>( istream &input, UserLogin &user )
{
    input >> user.id;
    input >> user.login;
    input >> user.logout;

    return input;
}

演员表会让你读到一个临时的，然后立即丢弃。

Answer 2

input >> (type) var;

错了，不要这样做。做简单的

input >> var;

Answer 3

#ifndef STRING_H
#define STRING_H

#include <iostream>
using namespace std;

class String{
    friend ostream &operator<<(ostream&,const String & );


    friend istream &operator>>(istream&,String & );

public:
    String(const char[] = "0");
    void set(const char[]);
    const char * get() const;
    int length();

    /*void bubbleSort(char,int);
    int binSearch(char,char,int);

    bool operator==(const String&);
    const String &operator=(const String &);
    int &operator+(String );*/

private:
        const char *myPtr;
    int length1;

};
#endif

C ++输入操作符重载

3 个答案: