C++ error: no matching constructor for initialization of

In memberwise assignment in C++, you can set the values of one object to another object of the same class. I initialize a rectangle object with some values and create another rectangle object but assign the value of the first into the second.

It's giving me an error. Why?

Rectangle.h

#ifndef RECTANGLE_H #define RECTANGLE_H class Rectangle { private: double length; double width; public: Rectangle(double, double); double getLength() const; double getWidth() const; }; Rectangle::Rectangle(double l, double w) { length = l; width = w; } double Rectangle::getWidth() const { return width; } double Rectangle::getLength() const { return length; } #endif 

Rectangle.cpp

#include <iostream> #include "rectangle.h" using namespace std; int main() { Rectangle box1(10.0, 10.0); Rectangle box2; cout << "box1's width and length: " << box1.getWidth() << ", " << box1.getLength() << endl; cout << "box2's width and length: " << box2.getWidth() << ", " << box2.getLength() << endl; box2 = box1; cout << "box1's width and length: " << box1.getWidth() << ", " << box1.getLength() << endl; cout << "box2's width and length: " << box2.getWidth() << ", " << box2.getLength() << endl; return 0; } 

Error when I compile:

skipper~/Desktop/Programming/Memberwise: g++ rectangle.cpp rectangle.cpp:7:12: error: no matching constructor for initialization of 'Rectangle' Rectangle box1(10.0, 10.0); ^ ~~~~~~~~~~ ./rectangle.h:4:7: note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 2 were provided class Rectangle { ^ ./rectangle.h:4:7: note: candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 2 were provided 1 error generated. 

2 Answers

In the line

Rectangle box2; // no default constructor, error 

you are trying to invoke the default constructor of Rectangle. The compiler does not generate such a default constructor anymore, because your Rectangle has a user defined constructor that takes 2 parameters. Therefore, you need to specify the parameters, like

Rectangle box2(0,10); 

The error I get when compiling your code is:

Rectangle.cpp:8:15: error: no matching function for call to 'Rectangle::Rectangle()' Rectangle box2;

A solution is to create a default constructor for Rectangle, since it is not automatically generated anymore due to your user defined one:

Rectangle(); // in Rectangle.h Rectangle::Rectangle(){} // in Rectangle.cpp (or Rectangle::Rectangle() = default; in C++11) 

Another solution (and the preferable one, since it doesn't leave the data un-initialized) is to assign default arguments to your existing constructor.

Rectangle::Rectangle(double l = 0, double w = 0); // only in Rectangle.h 

In this way, you make your class Default-Constructible.

A compiler generated default constructor is only generated if you have no defined constructors. You define a constructor, so if you want a default constructor you have to provide it yourself. Probably the easiest (arguably) is to provide it by using default arguments in your two argument constructor:

Rectangle(double l=0, double w=0) 

Also you should use the inline keyword as shown below or you may find you get linker errors:

inline Rectangle::Rectangle(double l, double w) { length = l; width = w; } inline double Rectangle::getWidth() const { return width; } inline double Rectangle::getLength() const { return length; }