CODEWITHSUNDEEP
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user550738
user550738

Reputation:

How do I pass an enum by reference in this simple example?

I'm having a problem in my code, I hacked up this simple example to illustrate it.

I have a Player class that has a public enum PlayerType. I have a Manager class with a createPlayer method that accepts a reference to a player and a player type.

But I can't get it to compile -- note, I can't change the signature of the createPlayer method, each param must be an object reference.

What am I doing wrong?

Player.h

#ifndef PLAYER_H
#define PLAYER_H

using namespace std;

class Player {
  public:
    Player();
    enum PlayerType { FORWARD, DEFENSEMAN, GOALIE };
    void setType(PlayerType);
  private:
    PlayerType type;
};

#endif

Player.cc

#include <iostream>

using namespace std;

#include "Player.h"

Player::Player() {
}

void Player::setType(PlayerType type) {
  this->type = type;
}

Manager.h

#ifndef MANAGER_H
#define MANAGER_H

using namespace std;

#include "Player.h"

class Manager {
  public:
    void createPlayer(Player& player, PlayerType& playerType);
};

#endif

Manager.cc

#include <iostream>

using namespace std;

#include "Player.h"

#include "Manager.h"

void Manager::createPlayer(Player& player, PlayerType& playerType) {
  cout << "inside Manager::createPlayer" << endl;
}

Main.cc

#include <iostream>

using namespace std;

#include "Player.h"
#include "Manager.h"

int main() {

  Manager manager;
  Player player;
  manager.createPlayer(player, Player::FORWARD);

  return 0;
}

When I compile gcc -o a.out *.cc *.h I get this error:

In file included from Main.cc:6:0:
Manager.h:10:39: error: ‘PlayerType’ has not been declared
Main.cc: In function ‘int main()’:
Main.cc:12:47: error: no matching function for call to ‘Manager::createPlayer(Player&, Player::PlayerType)’
Main.cc:12:47: note: candidate is:
Manager.h:10:10: note: void Manager::createPlayer(Player&, int&)
Manager.h:10:10: note:   no known conversion for argument 2 from ‘Player::PlayerType’ to ‘int&’
In file included from Manager.cc:7:0:
Manager.h:10:39: error: ‘PlayerType’ has not been declared
Manager.cc:9:44: error: ‘PlayerType’ has not been declared
Manager.h:10:39: error: ‘PlayerType’ has not been declared

What do I do to make this work?

Upvotes: 0

Views: 720

Answers (3)

Vlad from Moscow
Vlad from Moscow

Reputation: 310950

The problem is that in this call

manager.createPlayer(player, Player::FORWARD);

the second argument is a temporary object, You may not bind non const reference with a temporary object.

So you should declare function as

void Manager::createPlayer(Player& player, const Player::PlayerType& playerType)

Though I do not see a great sense to use the reference. I would declare the function simpler

void Manager::createPlayer(Player& player, Player::PlayerType playerType)

withou the reference.

Upvotes: 1

Etienne
Etienne

Reputation: 16867

to be able to use a reference you need to store the value into a variable.

int main() {

  Manager manager;
  Player player;
  Player::PlayerType t = Player::FORWARD;
  manager.createPlayer(player,t);

  return 0;
}

Upvotes: 2

gerrit zijlstra
gerrit zijlstra

Reputation: 754

You need to change

void createPlayer(Player& player, Player::PlayerType& playerType);

to

void createPlayer(Player& player, const Player::PlayerType& playerType);

Passing Player::FORWARD as a parameter creates a temporary PlayerType value that can only be passed as a const reference or by value.

Upvotes: 1

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