Thread: Why does this work?

The following is quite long but ignore the class declarations. Im confused about the address assignments to the object pointers in main()

Code:

#include <iostream>
#include <cstring>
using namespace std;
class twodshape {
	double x,y;
	char name[20];
public:
	virtual double area() {
		cout<<"Must be redefined."<<endl;
		return 0.0;
	}
	double X() { return x; }
	double Y() { return y; }
	void X(double a) { x=a; }
	void Y(double a) { y=a; }
	twodshape(double a,double b,char *str) {
		x=a;
		y=b;
		strcpy(name,str);
	}
};
class rectangle : public twodshape {
	bool sqr;
public:
	double area() {
		return X()*Y();
	}
	rectangle(double a,double b):twodshape(a,b,"rectangle") {
		if(a==b) sqr=true;
	}
	bool Sqr() { return sqr; }
};
int main() {
	twodshape *obs[3];
	obs[0]=&rectangle(10,10); //here (isn't this the same as saying p=&5 instead of p=&var)
	obs[1]=&rectangle(5,15); //and here
	obs[2]=&twodshape(7,8,"generic"); //and here
	cout<<"Shape 1 area: "<<obs[0]->area()<<endl;
	cout<<"Shape 2 area: "<<obs[1]->area()<<endl;
	cout<<"Shape 3 area: "<<obs[2]->area()<<endl;
	return 0;
}

First time I saw it I dismissed it as wrong, but decided to try compiling it anyway. But it actually worked. What I dont understand is how a pointer can be assigned to an object that isnt even declared properly. Or is there something I missed out...

It didnt work!
It just looked like it worked.

twodshape *obs[3];
obs[0]=&rectangle(10,10);

The first line is fine. The second is problematical. This says make a temporary object( of lifetime until the end of the expression its used in) of class rectangle using (10,10) as constructor parameters and take the address of it and stuff it in obs[0]. Why do you think this is a problem?
Why do you think it worked?
Exactly same problem done twice more.

Because the data is still there even though the memory is deallocated. The program has no need to fill the data with 0's or anything as that would just be a waste of time. The point is it's only a matter of time before another object takes its place and ovewrites all or part of the data and if you try to edit it, you risk editting something else that was allocated in the same place as the temporary object was.