C++ Delegated Constructor

Question

I am trying to use a delegated constructor and am trying to follow the format found in this question and this question, however, I am still having issues.

My player.h file is this:

#ifndef PLAYER_H_
#define PLAYER_H_

#include <string>

class Player
{
public:
   Player(void);
   Player(std::string name, int score);
   ~Player();
protected:
   std::string name_;
   int score_;
};

#endif

My player.cpp file is this:

#include "player.h"
Player::Player(std::string name, int score)
{
   score_ = score;
   name_ = name;
}

Player::Player(void) : Player(NULL,0)
{

}

However, when I try to compile, I get the following error:

1>a:\projects\test\src\player.cpp(5): error C2614: 'Player' : illegal member initialization: 'Player' is not a base or member

What am I doing wrong? If it is relevant, I am using VS2012.

As far as I know (though I don't know much), vs2012 doesn't support delegated constructors. — Michael Krelin - hacker, Sep 24 '12 at 20:39
You want to use delegating constructors but don't even know how to use ordinary initializer lists? I think you might benefit from backing up a bit... — Kerrek SB, Sep 24 '12 at 20:40
@KerrekSB I was using initializer lists, but I thought they might be causing the issue so I got rid of them. I'm not sure why you're trying to discourage people who are learning the language from learning the different ways to call a constructor. — , Sep 24 '12 at 20:45
@Kyryx: OK, fair enough - but with initalizer lists, the second constructor would have been easy to write as `Player() : name_(), score_() { }`, so not having delegating constructors wouldn't have been a big issue... — Kerrek SB, Sep 24 '12 at 20:50

score 14 · Accepted Answer · edited Nov 27 '12 at 16:59

14

If it is relevant, I am using VS2012.

It is, because Visual Studio doesn't implement this C++11 feature. Sorry. There are quite a lot of C++11 features they don't implement.

edited Nov 27 '12 at 16:59

T.E.D.

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answered Sep 24 '12 at 20:39

Nicol Bolas

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Oh.. Well that would explain it. Thank you – Sep 24 '12 at 20:41
1

Gratz on your gold [tag:c++11] badge. :) I thought I could beat you to it before you reached 200 answers, but meh. – Xeo Sep 25 '12 at 09:26
I can't understand why Visual Studio doesn't implement this... Anyways, thanks for the help! – Janman May 23 '13 at 18:32
I believe delegating constructors were introduced in VS 2013 (VS12, _MSC_VER 1800). – Luv2code Oct 02 '15 at 18:53

score 7 · Answer 2 · answered Sep 24 '12 at 20:49

7

This isn't an answer to your question, but even though your compiler doesn't support delegating constructors, I want to address a few separate issues that your code would otherwise have suffered from:

Use initializer lists, not assignment.
When constructing heavy objects, pass by value and move.
You cannot initialize a std::string from a null pointer. If you want an empty string, pass an empty string.
You should only very rarely and in very exceptional cases have a destructor.

Putting it all together, we arrive at the following code:

class Player
{
public:
   Player(std::string name, int score)
   : name_(std::move(name))
   , score_(score)
   { }

   Player()
   : Player("", 0)
   { }

protected:
   std::string name_;
   int         score_;
};

answered Sep 24 '12 at 20:49

Kerrek SB

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Thank you, helpful feedback. Do you think you can explain point 2 though? – Sep 24 '12 at 20:52
1

@Kyryx: The point is that you should be able to say both `Player(str, 1)`, which makes a copy, and `Player(std::string("Hello"), 2)`, which can *move* the resource without an additional allocation. Passing to the constructor by value and moving allows you to permit both cases with maximal efficiency. – Kerrek SB Sep 24 '12 at 20:53
Good catch there with the string object receiving 0. On Mac OS X, `std::string str(0);` crashes immediately. – bobobobo Jun 15 '13 at 16:26

C++ Delegated Constructor

2 Answers2