c ++ - 具有继承的未声明标识符（运算符ostream）[重复]

Posted 2023-02-23

【中文标题】c ++ - 具有继承的未声明标识符（运算符ostream）[重复]

【英文标题】：c++ - undeclared identifier (operator ostream) with inheritance [duplicate]

【发布时间】：2017-06-10 14:21:25

【问题描述】：

我不知道为什么会出现错误，因为对我来说一切都很好，我已经加载了所有代码，但错误出现在 print operator only 函数中。当我运行程序时，他会带我到这个函数。

我有一个错误，但我不明白为什么。 非常感谢帮助。

当我运行程序时，错误就在这里（在 CatsPen.h 中）：

Error   1   error C2065: 'os' : undeclared identifier   
c:\users\name\documents\visual studio 2013\projects\exe8\CatsPen.h  33  1   
EXE8

 friend ostream& operator<<(ostream&, const CatsPen& other)
    for (int i = 0; i < other.countStreet; i++)
        os << other.street[i] << endl;
    
    for (int i = 0; i < other.countSiami; i++)
        os << other.siami[i] << endl;
    
    return os;
    

主要：

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

using namespace std;


int main()

CatsPen pen1;

int choice = -1;
while (choice == -1)
    cin >> choice;
    cout << "Enter your choice: " << endl;
    cout << "1-add street cat " << endl;
    cout << "2-add siami cat " << endl;
    cout << "3-print cats " << endl;
    cout << "4-print how many cats " << endl;
    cout << "5-exit" << endl;

    if (choice == 1)
        pen1.addStreet();
    


system("pause");
return 0;

CatsPen.h：

include "Cat.h"
#include <iostream>
using namespace std;
#ifndef CatsPen_H
#define CatsPen_H

class CatsPen
private:
StreetCat * street;
SiamiCat * siami;
int countStreet;
int countSiami;
int numOfCats;
int emptyCage;

public:
CatsPen();
~CatsPen();
int getCountCat()
    return countStreet + countSiami;


bool Place();
bool addStreet();
bool addSiami();

friend ostream& operator<<(ostream&, const CatsPen& other)
    for (int i = 0; i < other.countStreet; i++)
        os << other.street[i] << endl;
    
    for (int i = 0; i < other.countSiami; i++)
        os << other.siami[i] << endl;
    
    return os;

;
#endif;

CatsPen.cpp：

catsPen.h"

CatsPen::CatsPen()
this->street = NULL;
this->siami = NULL;
this->numOfCats = 0;
this->countStreet = 0;
this->countSiami = 0;
this->emptyCage = 5;


CatsPen::~CatsPen()
for (int i = 0; i < countStreet; i++)
    delete &street[i];

delete[] street;

for (int i = 0; i < countStreet; i++)
    delete &street[i];

delete[]siami;


bool CatsPen::Place()
if (emptyCage > 0)
    return true;


cout << "no have place in the pen" << endl;
return false;


bool CatsPen::addStreet()
if (Place() == true)
    if (countStreet == 0)
        this->street = new StreetCat[1];
        cin >> this->street[countStreet];
        cout << this->street[countStreet];
    
    else if (countStreet > 0)
        StreetCat* copyArray = new StreetCat[this->countStreet + 1];
        for (int i = 0; i < countStreet; i++)
            copyArray[i] = street[i];
            cin >> copyArray[countStreet];
            delete[] street;
            cout << copyArray[countStreet];
            street = copyArray;
        
        countStreet++;
        emptyCage--;
    

    cout << "no have place in the pen" << endl;
    return false;



bool CatsPen::addSiami() //add siami cat to the pen
if (Place() == true) 
    if (countSiami == 0) 
        this->siami = new SiamiCat[1];
        cin >> this->siami[countSiami];
        cout << siami[countSiami];
    
    else if (countSiami > 0) 
        SiamiCat*copyArray = new SiamiCat[this->countSiami + 1];
        for (int i = 0; i < countSiami; i++)
            copyArray[i] = siami[i];
        cin >> copyArray[countSiami];
        cout << copyArray[countSiami];
        delete[]siami;
        siami = copyArray;
    
    countSiami++;
    emptyCage--;
    return true;


cout << "no have place in the pen" << endl;
return false;

谢谢...

【问题讨论】：

通函包括？？

@liran 你忘了在定义朋友ostream&运算符中指定参数名称os

请花一些时间到read about how to ask good questions，学习如何创建Minimal, Complete, and Verifiable Example 并向我们展示。

operator<<() 的参数列表没有为第一个参数提供名称。

您无法理解“'os' : undeclared identifier”的哪一部分？

【参考方案1】：

这个定义有错别字

 friend ostream& operator<<(ostream&, const CatsPen& other)
                                   ^^^ 
    for (int i = 0; i < other.countStreet; i++)
        os << other.street[i] << endl;
    
    for (int i = 0; i < other.countSiami; i++)
        os << other.siami[i] << endl;
    
    return os;
    

参数名os漏掉了。

 friend ostream& operator<<(ostream &os, const CatsPen& other)
                                     ^^^