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Polymorphic calls not working!!

keh k lenge (49)
Shape<---Triangle<---IsoTriangle

If I run code below I get the following error
IsoTriangle.cpp:36:8: error: no match for ‘operator<<’ (operand types are ‘std::ostream {aka std::basic_ostream<char>}’ and ‘Shape’)
cout << *shp << endl; 

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  IsoTriangle rect(10);
  Shape* shp = &rect;
  //cout << typeid(shp).name() << endl;
  //cout << typeid(*shp).name() << endl;

  //This line causes error saying compiler cannot find operator<<
  cout << *shp << endl;
  //rect.draw('2', 'w');
}



My Shape header
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#ifndef SHAPE_H
#define SHAPE_H
#include<string>
#include<vector>
#include<iostream>
using namespace std;

class Shape {
private:
	static int num;
	int id_num;
	string generic_name;
	string descriptive_name;
public:

	vector< vector<char> > str_rep;

	//getters
	virtual int  get_id() const;
	virtual string  get_generic_name() const;
	virtual string  get_descriptive_name() const;
	int num_incr();

	//setters
  virtual void set_generic_name(string name);
	virtual void  set_desciptive_name(string name);
	virtual void  set_id(int id);

	//pure_virtuals
	virtual void generate_string_representation() = 0;
	virtual void scale(int factor) = 0;
	virtual float area() const = 0;
	virtual float perimeter() const = 0;
	virtual vector< vector<char> > draw(char penChar, char fillChar) const = 0;
	virtual float calculate_box_height() const = 0;
	virtual float calculate_box_width() const = 0;
	virtual float scrn_area() const = 0;
	virtual float scrn_perimeter() const = 0;
	virtual string toString() const = 0;
	// friend ostream& operator<<(ostream& os, const vector< vector<char> >& grid);
	// friend ostream& operator<<(ostream& os, const Shape& obj);
};

#endif


Shape cpp
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#include"Shape.h"


int Shape::num = 0;

int Shape::get_id() const{
	return this->id_num;
}

string Shape::get_generic_name() const{
	return this->generic_name;
}

string Shape::get_descriptive_name() const{
	return this->descriptive_name;
}

int Shape::num_incr() {
	Shape::num++;
	return Shape::num;
}

void Shape::set_generic_name(string name) {
	this->generic_name = name;
}

void Shape::set_desciptive_name(string name) {
	this->descriptive_name = name;
}

void Shape::set_id(int id) {
	this->id_num = id;
}


My triangle header
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#ifndef TRIANGLE_H
#define TRIANGLE_H
#include"Shape.h"

class Triangle: public Shape{
};

#endif


IsoTriangle.h
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#ifndef IsoTriangle_H
#define IsoTriangle_H
#include"Triangle.h"
#include<typeinfo>
#include<string>
#include <cmath>

class IsoTriangle : public Triangle {
	public:
		int height;
		int base;
		IsoTriangle(int base);
		~IsoTriangle();

		void generate_string_representation(){
			this->str_rep.resize(this->height);
      int point = (this->base / 2) ;
      int count = 0;
			for (int x = 0; x <= this->height - 1; x++) {
				this->str_rep[x].resize(this->base);
				for (int y = 0; y <= this->base - 1; y++) {
          if(y >= point - count && y<= point + count){
            this->str_rep[x].push_back('*');
          }else{
            this->str_rep[x].push_back(' ');
          }
				}
        count++;
			}
		}

		void scale(int factor) {
			if (this->base + (2 * factor) >= 1) {
				this->base = this->base +  (2 * factor);
        this->height = (this->base + 1)/2;
				this->generate_string_representation();
			}
		}

		float area() const{
			return float(float(this->height * this->base)/2);
		}

		float perimeter() const{
      int b_sq = this->base * this->base;
      int h_sq = this->height * this->height;
			return float(this->base + (2 * pow(((.25 * b_sq) + h_sq), .5)));
		}

		vector< vector<char> > draw(char penChar, char fillChar) const{
			const int b = this->base;
			const int h = this->height;
			vector< vector<char> > temp(h, vector<char>(b));
      int point = (this->base / 2) ;
      int count = 0;
			for (int x = 0; x <= this->height - 1; x++) {
				for (int y = 0; y <= this->base - 1; y++) {
          if(y >= point - count && y<= point + count){
            temp[x].push_back(penChar);

          }else{
            temp[x].push_back(fillChar);

          }
				}
        count++;
			}
			return temp;
		}

		float calculate_box_height() const{
			return this->height;
		}

		float calculate_box_width() const{
			return this->base;
		}

		float scrn_area() const{
			return float(this->height * this->height);
		}

		float scrn_perimeter() const{
			return float(4 * (this->height - 1));
		}

    string toString() const{
      string abcd;
      abcd = string("Shape Information") + "\n";
      abcd = abcd + "-----------------" + "\n";
      abcd = abcd + "Static type: " + typeid(this).name() + "\n";
      abcd = abcd + "Dynamic type: " + typeid(this).name() + "\n";
      abcd = abcd + "Generic Name: " + this->get_generic_name() + "\n";
      abcd = abcd + "Description: " + this->get_descriptive_name() + "\n";
      abcd = abcd + "id: " + to_string(this->get_id()) + "\n";
      abcd = abcd + "B. box width: " + to_string(this->calculate_box_width()) + "\n";
      abcd = abcd + "B. box height: " + to_string(this->calculate_box_height()) + "\n";
      abcd = abcd + "Scr area: " + to_string(this->scrn_area()) + "\n";
      abcd = abcd + "Geo area: " + to_string(this->area()) + "\n";
      abcd = abcd + "Scr Perimeter: " + to_string(this->scrn_perimeter()) + "\n";
      abcd = abcd + "Geo Perimeter: " + to_string(this->perimeter()) + "\n";
      return abcd;
    }

		friend ostream& operator<<(ostream& os, const Shape& obj) {
			os << "Shape Information" << endl;
			os << "-----------------" << endl;
			os << "Static type: " << typeid(&obj).name() << endl;
			os << "Dynamic type: " << typeid(obj).name() << endl;
			os << "Generic Name: " << obj.get_generic_name() << endl;
			os << "Description: " << obj.get_descriptive_name() << endl;
			os << "id: " << obj.get_id() << endl;
			os << "B. box width: " << obj.calculate_box_width() << endl;
			os << "B. box height: " << obj.calculate_box_height() << endl;
			os << "Scr area: " << obj.scrn_area() << endl;
			os << "Geo area: " << obj.area() << endl;
			os << "Scr Perimeter: " << obj.scrn_perimeter() << endl;
			os << "Geo Perimeter: " << obj.perimeter() << endl;
      return os;
		}
};

ostream& operator<<(ostream& os,  const vector< vector<char> >& grid) {
  for (const vector<char>& vec : grid) {
    for (const char& ch : vec) {
      os << ch;
    }
    os <<"\n";
  }
  return os;
}

#endif // !IsoTriangle_H


IsoTriangle.cpp
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#include "IsoTriangle.h"
#include <iostream>

IsoTriangle::IsoTriangle(int base) {
	if(base<=0){
		std::cout << "Cannot pass values less than or equal to 0 \n";
		this->~IsoTriangle();
	}
  if(base%2==0){
    base++;
  }
	this->base = base;
  this->height = (base + 1)/2;
	this->set_id(this->num_incr());
  this->set_generic_name("IsoTriangle");
  this->set_desciptive_name("Generic IsoTriangle");
}

IsoTriangle::~IsoTriangle() {

}

int main()
{
	IsoTriangle rect(10);
	IsoTriangle rect_1(0);
	IsoTriangle rect_2(-10);
	cout << rect << endl;
  cout << rect.draw('2', 'w') << endl;
  rect.scale(2);
  cout << rect.draw('2', 'w') << endl;
  cout << rect.toString() << endl;
  Shape* shp = &rect;
  cout << typeid(shp).name() << endl;
  cout << typeid(*shp).name() << endl;
  cout << *shp << endl;
  //rect.draw('2', 'w');
}
Peter87 (11178)
There is no operator<< that takes a Shape as argument.
keh k lenge (49)
There is operator<< with Shape argument somehow its indented badly IDK why
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friend ostream& operator<<(ostream& os, const Shape& obj) {
			os << "Shape Information" << endl;
			os << "-----------------" << endl;
			os << "Static type: " << typeid(&obj).name() << endl;
			os << "Dynamic type: " << typeid(obj).name() << endl;
			os << "Generic Name: " << obj.get_generic_name() << endl;
			os << "Description: " << obj.get_descriptive_name() << endl;
			os << "id: " << obj.get_id() << endl;
			os << "B. box width: " << obj.calculate_box_width() << endl;
			os << "B. box height: " << obj.calculate_box_height() << endl;
			os << "Scr area: " << obj.scrn_area() << endl;
			os << "Geo area: " << obj.area() << endl;
			os << "Scr Perimeter: " << obj.scrn_perimeter() << endl;
			os << "Geo Perimeter: " << obj.perimeter() << endl;
      return os;
}
Last edited on
Peter87 (11178)
Ah, I see. I wasn't expecting it to be in the IsoTriangle class.

When you declare a function as a friend inside a class it will not be considered during the usual lookup process outside the class.

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class A
{
	friend void f();
};

int main()
{
	A a;
	f(); // error: ‘f’ was not declared in this scope
}


The reason it normally works for the << and >> operators is thanks to something called argument-dependent lookup (ADL). If a class object is passed as argument to a function the compiler will in addition look for a matching function within that class. 

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class A
{
	friend void g(A);
};

int main()
{
	A a;
	g(a); // This works fine thanks to ADL.
}


In your code you are passing a Shape reference to the << operator but it cannot find a match. There is no such operator declared in the global scope, nor is it in the Shape class. The IsoTriangle class is not considered.
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