Thread: no default constructor error

I get the error:

error C2512: 'Mouse' : no appropriate default constructor available
Error executing cl.exe.

in the following code, and I can't figure out why the class Mouse default constructor is called:

Code:

#include <iostream>
using namespace std;

class Mouse
{
public:
     Mouse(int n)
	 {
		 length = n;
	 }	
	 
	 void Display()
	 {
		 cout<<length<<endl;
	 }

	 int GetLength()
	 {
		 return length;
	 }
	 
private:
     int length;
};

class Cat
{
public:
	Cat(Mouse m)//********ERROR
	{
		member1 = m;
	}
	

	void Display()
	{
		cout<<member1.GetLength()<<endl;
	}

private: 
	Mouse member1; 
};

int main()
{
	Mouse my_Mouse(3);

	Cat my_Cat(my_Mouse);

	my_Cat.Display();

	
    return 0;
}

If I add a default constructor to class Mouse, then it works fine. When is the default constructor called?

It would be called if you didn't specify any parameters. Like this:
Mouse my_mouse;

It's because in your Cat class you have as a private member the statement

Code:

Mouse member1;

What do you think this does? Well that would call the default constructor at some point.

Mouse member1;

What do you think this does? Well that would call the default constructor at some point.

That's not obvious. This doesn't call the default constructor:

Mouse a_Mouse(3);
Mouse m = a_Mouse;

So, what's the step- by-step process of what's happening(--not at the assembly level). The code doesn't work even if main is empty, and I never try to instantiate an object.

Originally posted by 7stud
Mouse member1;

What do you think this does? Well that would call the default constructor at some point.

That's not obvious. This doesn't call the default constructor:

Mouse a_Mouse(3);
Mouse m = a_Mouse;

You're right that doesn't call the default constructor. That calls the copy constructor. Even though you didn't write your own copy constructor your class is provided with one.

I wasn't trying to sound like an $$$ in my post. Maybe that's the way it came off, sorry bout that.