英文:
C++ overloading + operator runs into Problem with Constants
问题
在第40行出现了以下错误：
error: no match for 'operator+' (operand types are 'const Vec2' and 'const Vec2')
以下是您的代码：
#include <iostream>using namespace std;class Vec2 {private:double X;double Y;public:Vec2(double x, double y){X = x;Y = y;}double getX() const {return X;}double getY() const {return Y;}Vec2 operator+(Vec2 v ){Vec2 res(v.getX()+X, v.getY()+Y);return res;}};ostream& operator<<(ostream& s , const Vec2& my_vec){s << " ( " << my_vec.getX()<< " , " << my_vec.getY() << " ) ";return s ;}int main(){Vec2 const a(3,4); cout << a << endl;Vec2 const b(3,4); cout << b << endl;Vec2 c(a+b); cout << c << endl;return 0;}
有趣的是，当您从第37行中的'a'中移除"const"关键字时，一切都正常工作，但我不想通过更改主函数的内容来修复错误。我对运算符重载还不熟悉，所以感谢您的帮助。
英文:
I defined a Vec2 object that should represent a 2d-vector. I tried to overload the + operator to implement vectoraddition but I get following error in Line 40:
error: no match for 'operator+' (operand types are 'const Vec2' and 'const Vec2')
Here's my code:
#include <iostream>using namespace std;class Vec2 {private:double X;double Y;public:Vec2(double x, double y){X = x;Y = y;}double getX() const {return X;}double getY() const {return Y;}Vec2 operator+(Vec2 v ){Vec2 res(v.getX()+X, v.getY()+Y);return res;}};ostream& operator<<(ostream& s , const Vec2& my_vec){s << " ( "<< my_vec.getX()<< " , "<< my_vec.getY() <<" ) " ;return s ;}int main(){Vec2 const a(3,4); cout << a << endl;Vec2 const b(3,4); cout << b << endl;Vec2 c(a+b); cout << c << endl;return 0;}
Interestingly when you remove the "const" keyword from a in line 37 everything works, but I don't wan't to fix the error by changing the content of the main function.
I am new to operator overloading, so thanks for the help.
答案1
得分: 2
The left operand, a, is const but your operator+ is not const qualified.
You simply need to make it so. Also, instead of taking the right operand, b, by value, you can (optionally) take it by const reference:
Vec2 operator+(const Vec2& v) const {// ^^^^^
An alternative is to only define operator+= as a member function and then to make operator+ a free function:
class Vec2 {public://...Vec2& operator+=(const Vec2& v) { // this changes *this, so not const qual.X += v.X;Y += v.Y;return *this;}};Vec2 operator+(const Vec2& lhs, const Vec2& rhs) {Vec2 result(lhs);result += rhs; // uses the member function operator+=return result;}
Alternatively:
Vec2 operator+(Vec2 lhs, const Vec2& rhs) {return lhs += rhs; // uses the member function operator+=}
英文:
The left operand, a, is const but your operator+ is not const qualified.
You simply need to make it so. Also, instead of taking the right operand, b, by value, you can (optionally) take it by const reference:
Vec2 operator+(const Vec2& v) const {// ^^^^^
An alternative is to only define operator+= as a member function and then to make operator+ a free function:
class Vec2 {public://...Vec2& operator+=(const Vec2& v) { // this changes *this, so not const qual.X += v.X;Y += v.Y;return *this;}};Vec2 operator+(const Vec2& lhs, const Vec2& rhs) {Vec2 result(lhs);result += rhs; // uses the member function operator+=return result;}
Alternatively:
Vec2 operator+(Vec2 lhs, const Vec2& rhs) {return lhs += rhs; // uses the member function operator+=}
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