How to sort the elements of a std::vector of pointers to instances of derived classes

User 11251399

I'm programming a 2D RPG game that uses an array of derived class instance pointers. For clarity I provide a code example in C++. I would like to sort the elements of the entities array based on the worldY value of each element.

main.cpp:

/*
* result:
* player
* object
* object
* npc
* npc
* 2 npc y: 30
* 1 npc y: 6
* 1 object y: 20
* 2 object y: 10
* player y: 0
*/

#include #include #include #include "Entity.h"
#include "Npc.h"
#include "Player.h"
#include "Object.h"

int main()
{
Player* player = new Player();

std::vector objs;
std::vector npcs;
std::vector entities;

Entity\* tmp = new OBJ\_o();
objs.push\_back(tmp);
objs.at(0)->worldY = 20;
objs.at(0)->ID = "1";

tmp = new OBJ\_o();
objs.push\_back(tmp);
objs.at(1)->worldY = 10;
objs.at(1)->ID = "2";

tmp = new NPC();
npcs.push\_back(tmp);
npcs.at(0)->worldY = 6;
npcs.at(0)->ID = "1";

tmp = new NPC();
npcs.push\_back(tmp);
npcs.at(1)->worldY = 30;
npcs.at(1)->ID = "2";

//--------------- update -------------------
player->update();

for (auto iter\_objs = objs.begin(); iter\_objs != objs.end(); ++iter\_objs)
{
    (\*iter\_objs)->update();
}

for (auto iter\_npcs = npcs.begin(); iter\_npcs != npcs.end(); ++iter\_npcs)
{
    (\*iter\_npcs)->update();
}

//-------------- entities --------------------
entities.push\_back(player);

for (int i = 0; i < objs.size(); i++)
{
    if (!objs.at(i)->name.empty())
    {
        entities.push\_back(objs.at(i));
    }
}

for (int i = 0; i < npcs.size(); i++)
{
    if (!npcs.at(i)->name.empty())
    {
        entities.push\_back(npcs.at(i));
    }
}

// sort entities
std::sort(entities.begin(), entities.end());

//---------------- draw entities ------------------
for (auto iter = entities.begin(); iter != entities.end(); ++iter)
{
    std::cout << (\*iter)->ID << " ";
    (\*iter)->draw();
}

return 0;

}

Entity.h

#pragma once
#include

class Entity
{
public:
int worldY = 0;
std::string name;
std::string ID;

public:
virtual void update() { std::cout << "base" << std::endl; }
virtual void draw() { std::cout << "base y: -\n"; }

// Overload

Rick York

Please read the red text a little bit above your post. It talks about how this is not the appropriate place for a post of this nature.

"They have a consciousness, they have a life, they have a soul! Damn you! Let the rabbits wear glasses! Save our brothers! Can I get an amen?"

Pete OHanlon

As many people are about to tell you. There are no programming questions in the lounge. You should probably post this in the Quick Answers instead.

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User 11251399

OK