运算符 <<（操作数类型 std::ostream）不匹配 C++ OOP 和 Point
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/22714089/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
no match for operator << (operand types std::ostream) c++ OOP and Point
提问by Ahmad Adnan
I am trying to display p object of Point class that I have created through member function . I have passed Point p as argument in void displayPoint(Point p) member function of my program. But I am getting the following compilation error in my program!
我正在尝试显示我通过成员函数创建的 Point 类的 p 对象。我已将 Point p 作为参数传递给我的程序的 void displayPoint(Point p) 成员函数。但是我的程序中出现以下编译错误！
D:\OOP Assignment # 01\point.cpp[Error] no match for 'operator<<' (operand types are 'std::ostream {aka std::basic_ostream}' and 'Point')
D:\OOP 赋值 #01\point.cpp[Error] 不匹配 'operator<<'（操作数类型是 'std::ostream {aka std::basic_ostream}' 和 'Point'）
Here below is my code !!!
下面是我的代码！！！
#ifndef POINT_H
#define POINT_H
using namespace std; // For string usage
class Point
{
public:
Point(); // Default Constructor
Point(double, double, int); // Three argument constructor
void initialize(double, double, int);
void shift(Point p, int keyPress); // Shift the first point
void setValue(int value);
int getValue() const;
void setX();
double getX() const;
void setY();
double gety() const;
void AddPointValue(Point p2); /*This function add the TWO points
successfully reach on second true point co-ordinates*/
void displayPoint(Point p); //This will use to display value
bool checkCoordinates();
bool checkTime(); // Check time remaining
private:
double x;
double y;
int value;
};
#endif
IMPLEMENTATION FILE
实施文件
#include <iostream>
#include <conio.h>
#include <windows.h>
#include <string>
#include <time.h>
#include <stdio.h>
#include "point.h"
using namespace std;
Point::Point() // Default Constructor
{
x = 0.0;
y = 0.0;
value = 0;
}
Point::Point(double x1, double y1, int value1){
x = x1;
y = y1;
value = value1;
}
void Point::initialize(double init_x, double init_y, int init_value)
{
x = init_x;
y = init_y;
value = init_value;
}
void Point::shift(Point p, int keyPress){
Point maxSize;
Point minSize;
maxSize.x=80;
maxSize.y=40;
switch(keyPress)
{
case (VK_LEFT): // increment the x coord
p.x += 1;
if(p.x < minSize.x) p.x = minSize.x;
break;
case (VK_RIGHT): // decrement the x coord
p.x -= 1;
if(p.x > maxSize.x) p.x = maxSize.x;
break;
case (VK_UP): // decrement the y coord
p.y -= 1;
if(p.y < minSize.y) p.y = minSize.y;
break;
case (VK_DOWN): // increment the y coord
p.y += 1;
if(p.y > maxSize.y) p.y = maxSize.y;
break;
}
void Point::setValue(int value){
value = 0;
}
int Point::getValue() const{
return value;
}
void Point::setX(){
x = 0.0;
}
double Point::getX() const{
return x;
}
void Point::setY(){
y = 0.0;
}
double Point::gety() const{
return y;
}
void Point::displayPoint(Point p){
cout << p; // ERROR OCCURING HERE!!!
}
void Point::AddPointValue(Point p2){
}
bool Point::checkTime(){
}
采纳答案by taocp
void Point::displayPoint(Point p){
cout << p; // ERROR OCCURING HERE!!!
}
You have not overloaded <<operator to output the object of class Pointdirectly. So you can't do that. You can either add an overloaded operator<<or call corresponding get functions to get the data members of Point.
您没有重载<<运算符直接输出类的对象Point。所以你不能那样做。您可以添加重载operator<<或调用相应的 get 函数来获取Point.
For example, using get functions:
例如，使用 get 函数：
void Point::displayPoint(Point p){
cout << p.getX() << " " << p.gety() << endl;
}
You can take a look at Operator Overloading C++about overloading operator<<.
您可以查看有关重载的运算符重载 C++operator<<。
回答by fredoverflow
std::cout << myPointis just syntactic sugar for operator<<(std::cout, myPoint).
std::cout << myPoint只是operator<<(std::cout, myPoint).
So you have to overload operator<<for your class according to your needs:
所以你必须operator<<根据你的需要为你的班级超载：
std::ostream& operator<<(std::ostream& os, const Point& p)
{
os << p.getX() << "/" << p.getY();
return os;
}
回答by 4pie0
You have not defined
你还没有定义
std::ostream& operator<<( std::ostream&, const Point&);
This function is needed whenever you want to put a Pointinto std::ostreamusing <<as in:
每当您想将 aPoint放入std::ostreamusing时都需要此函数<<：
void Point::displayPoint(Point p){
cout << p; // operator<< must be overloaded to make this work
}
Possible implementation of this method for your purpose is:
为了您的目的，此方法的可能实现是：
std::ostream& operator<<( std::ostream& s, const Point& p)
{
s << p.getX() << ", " << p.getY();
return s;
}
You can look herefor some examples of overload for a very similar class as yours Point.
您可以在此处查看与您的 Point 非常相似的类的一些重载示例。
