缺少構造函數初始化

Question

嗨我想調試一個程序，我收到的錯誤之一是'缺少構造函數的初始化'。我是否需要預先聲明矢量，如何初始化它？

#include <iostream> 
#include <vector> 

using namespace std; 

class Point { 
private: 
    double x; 
    double y; 
public: 
    double get_x() { return x; } 
    double get_y() { return y; } 
    bool set_x(double arg) { 
     x = arg; 
     return true; 
    } 
    bool set_y(double arg) { 
     y = arg; 
     return true; 
    } 
    Point() : x(0), y(0) {} 
    Point(double argx, double argy) : x(argx), y(argy) { 
    } 
}; 


class Vector { 
private: 
    Point A; 
    Point B; 
public: 
    Point get_A() { return A; } 
    Point get_B() { return B; } 
    Vector(const Point &arg1, const Point &arg2) : A(arg1), B(arg2) 
    { 
     //this->A = arg1; 
     //this->B = arg2; 
     //A = arg1; 
     //B = arg2; 
    } 
    void set_A(const Point &arg) { 
     A = arg; 
    } 
    void set_B(const Point &arg) { 
     B = arg; 
    } 
    static Vector add_vector(const Vector &vector1, const Vector &vector2) { 
     if (&vector1.B != &vector2.A) { 

      //Error 1 Vector V1 No Matching constructor for initialization for 'vector' 

      Vector rval; 
      return rval; 
     } 

     Point one = vector1.A; 
     Point two = vector2.B; 

     Vector newvector(one, two); 
     //newvector.A = one; 
     //newvector.B = two; 
     return newvector; 

    } 
    Vector add_vector(const Vector &arg) { 
     // Type of this? Vector *; These three lines are equivalent: 
     //Point one = this->A; 
     //Point one = (*this).A; 
     Point one = A; 

     Point two = arg.B; 

     Vector newvector(one, two); 
     //newvector.A = one; 
     //newvector.B = two; 
     return newvector; 
    } 

}; 


int main() { 

    //Error 2 Vector v No Matching constructor for initialization for 'vector' 


    Vector v; 
    cout << "(" << v.get_A().get_x() << ", " << v.get_A().get_y() << "),\n" << 
    "(" << v.get_B().get_x() << ", " << v.get_B().get_y() << ")\n"; 

    //Error 3 Vector V1 No Matching constructor for initialization for 'vector' 


    Vector v1(1,2), v2(2,3); 
    Vector res = Vector::add_vector(v1, v2); 
    cout << "(" << res.get_A().get_x() << ", " << res.get_A().get_y() << "),\n" << 
    "(" << res.get_B().get_x() << ", " << res.get_B().get_y() << ")\n"; 

} 

Answer 1

你的問題在這裏是你的類不是默認構造。

Vector rval; 

需要默認的構造函數。由於您提供了用戶定義的構造函數，因此編譯器將不再爲您創建默認構造函數。

要創建Vector可以使用

Vector() = default; 

如果你有C++ 11或更高的默認構造函數，也可以使用

Vector() {} 

對於預C++ 11。

我不知道你正在嘗試與

Vector v1(1,2) 

Vector做需要兩個Point S和每個Point需要2倍的值。