对于实验室，我必须重载+运算符以添加同一类的对象，而==运算符以重载来自两个不同类的对象。重载==运算符的函数给我带来了很多麻烦（可能是因为我正在使用它比较不同类的对象区域）。我一直在不懈地寻找解决方案，并且尝试了所有发现的建议，但都没有成功，因此我不得不使用我的特定代码进行询问：
regionBootstrap.disable()现在，我没有使用重载的==来比较矩形和圆形区域，因为这样我会遇到很多编译器错误。你们能为我提供的将// OBJECTIVES:
// Add areas of 2 circles
// Add areas of 2 rectangles
// Compare areas of a circle and a rectangle
#include <iostream>
using namespace std;
// **********************Header*********************
class circle
{
friend bool operator==(const circle& ,
const circle&);
friend circle operator+(const circle& ,
const circle&);
public:
double radius, area;
void calcArea();
};
class rect
{
friend bool operator==(const rect& ,
const rect&);
friend rect operator+(const rect& ,
const rect&);
public:
double length, width, area;
void calcArea();
};
void displayMenu();
// **************************************************
// **********************Program*********************
int main()
{
int selection; // variable for menu selection
circle firstCircle; // objects from circle class
circle secondCircle;
rect firstRect; // objects from rect class
rect secondRect;
do {
displayMenu();
cin >> selection;
cout << endl;
if (selection == 1) // add area of 2 circles
{
firstCircle.calcArea();
secondCircle.calcArea();
circle thirdCircle = firstCircle + secondCircle;
cout << "The sum of your two circles is: " ;
cout << thirdCircle.area;
cout << endl;
}
else if (selection == 2) // add area of 2 rectangles
{
firstRect.calcArea();
secondRect.calcArea();
rect thirdRect = firstRect + secondRect;
cout << "The sum of your two rectangles is: " ;
cout << thirdRect.area;
cout << endl;
}
else if (selection == 3) // compare areas of a circle and a rectangle
{
firstCircle.calcArea();
firstRect.calcArea();
if (firstCircle.area == firstRect.area)
{
cout << "The area of your circle is equal to that of your rectangle." << endl;
}
else
{
cout << "The area of your circle is not equal to that of your rectangle." << endl;
}
}
else if (selection == 4) // exit program
{
return 0;
}
else
{
cout << "Please enter a valid selection.";
cout << endl;
continue;
}
} while (1);
return 0;
}
// **************************************************
// ******************Implementation******************
void circle::calcArea() // compute circle area
{
cout << "Enter a radius: ";
cin >> radius;
area = 3.14159265359 * radius * radius;
}
void rect::calcArea() // compute rectangle area
{
cout << "Enter a length: ";
cin >> length;
cout << "Enter a width: ";
cin >> width;
area = length * width;
}
bool operator==(const circle& firstCircle, // compare areas of objects
const rect& firstRect) // from different classes
{
return (firstCircle.area == firstRect.area &&
firstCircle.area == firstRect.area);
}
circle operator+ (const circle& firstCircle, // overload + for circle class
const circle& secondCircle)
{
circle circleSum;
circleSum.radius = firstCircle.radius + secondCircle.radius;
circleSum.area = firstCircle.area + secondCircle.area;
return circleSum;
}
rect operator+ (const rect& firstRect, // overload + for rect class
const rect& secondRect)
{
rect rectSum;
rectSum.length = firstRect.length + secondRect.length;
rectSum.width = firstRect.width + secondRect.width;
rectSum.area = firstRect.area + secondRect.area;
return rectSum;
}
void displayMenu() // menu options
{
cout << endl;
cout << "What would you like to do?" << endl;
cout << "1. Add the area of 2 circles."<< endl;
cout << "2. Add the area of 2 rectangles."<< endl;
cout << "3. Compare the area of a circle and a rectangle."<< endl;
cout << "4. Exit.";
}
// **************************************************
更改为firstCircle.area == firstRect.area的任何帮助将不胜感激。
答案 0 :(得分：4)
有很多方法可以编写所需的比较运算符。不干预类代码的最简单方法就是实现几个非成员运算符：
bool operator==(const circle& c, const rect& r) { return r.area == c.area; }
bool operator==(const rect& r, const circle& c) { return c.area == r.area; }
您可以将它们放在main函数上方的源文件中，或放入单独的头文件中。请注意，由于circle的成员是公开的，因此他们不必成为rect和area的朋友。
另一种方法是编写成员函数，但首先我们需要修复您现有的比较运算符：
class circle
{
public:
bool operator==(const circle& other) const { return area == other.area; }
// ...skipped...
};
它与您的版本有何不同？
this与other进行比较的成员函数，仅使用一个参数。circle类以外的地方打电话是公开的还可以使用const限定符来比较const对象，如下所示：
const circle c1 = getSomeCircle();
const circle& c2 = otherCircle;
c1 == c2; // Note: statement has no effect, despite it's syntax is correct.
c2 == c1;
非常量限定的比较将无法编译。总而言之，这是用C ++编写比较运算符的最惯用的方式。
最后，让我们添加圆圈以进行矩形比较：
class rect;
class circle
{
public:
bool operator==(const circle& other) const { return area == other.area; }
bool operator==(const rect&) const;
// ...skipped...
};
class circle { /* class definition skipped */ };
bool operator==(const rect& r) const { return area == r.area; }
首先，我们声明了rect类。当class被声明但未定义时（即 forward声明），我们可以使用指向其实例的指针ant引用，但不能使用实例本身。我们不能使用实例的原因之一是类的大小在定义之前是未知的。
然后，我们声明成员operator==接受对向前声明的类的引用，最后在rect定义之后，我们可以实现运算符。
rect与circle的比较可以完全相同的方式实现。
答案 1 :(得分：0)
运算符重载可以像下面这样重载。
#include <iostream>
using namespace std;
class rect;
class circle
{
friend bool operator==(const circle&,
const circle&);
//friend circle operator+(const circle&,
// const circle&);
public:
double radius, area;
//void calcArea();
public:
friend bool operator == (const circle&, const rect&);
double getArea()const { return area; }
};
class rect
{
friend bool operator==(const rect&,
const rect&);
//friend rect operator+(const rect&,
// const rect&);
public:
double length, width, area;
//void calcArea();
public:
friend bool operator == (const rect&, const circle&);
double getArea() const{ return area; }
};
int main(int argc, char *argv[]) {
circle c;
rect r;
if (c == r) {
cout << "It was a miracle a random circle is equal to a random rectangle in size!!!" << endl;
}
return 0;
}
bool operator == (const circle &c1, const circle &c2) {
return c1.getArea() == c2.getArea();
}
bool operator == (const rect &r1, const rect &r2) {
return r1.getArea() == r2.getArea();
}
bool operator == (const circle &c, const rect &r) {
return c.getArea() == r.getArea();
}
bool operator == (const rect &r, const circle &c) {
return c.getArea() == r.getArea();
}