Why is virtual function not being called?

Question

//GUITEXT
class guitext : public entity {
public:
    guitext(graphics *gfx, std::string _text, float _x, float _y, 
        float _size, float timeToLive);
    bool upd         


        

Answer 1

You should define entitys to contain pointers to entity. Slightly edited example derived from your code.

#include "stdafx.h"
#include <vector>
#include <string>

class entity 
{
public:
    virtual void draw() { }
};

class guitext : public entity 
{
public:
    void draw()
    {
        printf("draw");
    }
};

int _tmain(int argc, _TCHAR* argv[])
{
    std::vector<entity *> entitys;

    guitext g;

    entitys.push_back(&g); 

    for(int i = 0; i < (int)entitys.size(); i++) 
    { 
        entitys[i]->draw(); 
    }

    return 0;
}

Answer 2

Was the vector declared as vector<entity>? Then only the base class part can be stored there, i.e. you lose polymorphism (which only works through pointer or reference in C++).

Answer 3

You made a vector of entity. Those objects always have type entity. If you want to invoke polymorphism, they need to be pointers or references. How can a vector of entity store a guitext? There's not enough space, it doesn't know how to destroy it, etc etc.

Answer 4

You're storing Entitys, not pointers to objects of varying derived types of Entity.

Answer 5

What you've done is a bit concealed variant of slicing.

Answer 6

In addition, in your case it's not good idea to pass arguments by value, i suppose there will be very big quantity of objects that need to be redrawed. Better, by const reference, since functon doesn't change state of passed object inside.