No matching Function for a call [duplicate] - c++

Question

This question already has answers here:
What are all the member-functions created by compiler for a class? Does that happen all the time?
(5 answers)
Closed 6 years ago.
I've created very simple C++ project in codeblocks. I have header file (CVector.h), source file (CVector.cpp) and main code (code.cpp). When I try to compile the code I got the following message:
CVector.cpp|22|error: no matching function for call to 'CVector::CVector()'|
code.cpp
#include <iostream>
#include "CVector.h"
using namespace std;
int main () {
CVector vec1(1,2);
CVector vec2 (3,4);
cout << "vec1 data "; vec1.printData();
cout << "vec2 data "; vec2.printData();
cout << "vec1 area: " << vec1.area() << endl;
cout << "vec2 area: " << vec2.area() << endl;
return 0;
}
CVector.h
#ifndef CVECTOR_H
#define CVECTOR_H
class CVector
{
int x,y;
public:
CVector (int, int);
int area();
void printData ();
CVector operator+ (CVector param );
};
#endif // CVECTOR_H
CVector.cpp
#include <iostream>
#include "CVector.h"
using namespace std;
CVector::CVector (int a, int b) {
x=a;
y=b;
}
int CVector::area() {return x*y;}
void CVector::printData(){
cout << "X = " << x << ", Y = " << y << endl;
}
CVector CVector::operator+ (CVector param )
{
CVector temp;
temp.x=x + param.x;
temp.y=y + param.y;
return temp;
}
The error is related to the operator overloading function because it compiles without problems when I comment this function.

Answer 1

In operator+, the line
CVector temp;
needs a default constructor, but you didn't define one.
(If you define a non-default constructor, the compiler will not provide a default one.)
You can either define a default constructor, if you can decide on what suitable default values of the members could be, or you can write
CVector CVector::operator+ (CVector param )
{
CVector temp(x + param.x, y + param.y);
return temp;
}
or even
CVector CVector::operator+ (CVector param )
{
return CVector(x + param.x, y + param.y);
}

Answer 2

The problem in you operator + is this line:
CVector temp;
This lines creates a default-constructed CVector. However, your CVector class does not have a default constructor, hence the error. You need to add one to the class:
class CVector
{
int x,y;
public:
CVector(); // Added
//The rest as before
};
There are two ways to implement it. One:
CVector::CVector() {}
This will result in the members x and y remaining uninitialised.
Two:
CVector::CVector() : x(0), y(0) {}
This will initialise x and y to 0.
The second one is safer, the first one is faster. Which one to use depends on your goals for the class.
Unrelated, but in your two-parameter constructor, you should use the member initialisation list instead of assignments as well:
CVector::CVector(int a, int b) : x(a), y(b) {}
It doesn't really matter for primitive types such as int, but it's a good habit to grow. It's more efficient for members of a type with a nontrivial default constructor, and is actually nceessary for members of a type without a default constructor.