JordanW JordanW - 2 months ago 14
C++ Question

Sorting a vector of unique_ptr in VS 2013

I am attempting to make a

Deck
class that holds a vector of
unique_ptr<Card>
, but attempting to sort the vector results in this error:


Error 1 error C2280: 'std::unique_ptr>::
unique_ptr(const std::unique_ptr<_Ty,std::default_delete<_Ty>> &)'
: attempting to reference a deleted function


Looking through Stack Overflow, it looks like there is a bug in VS 2013 where vectors incorrectly tries to copy
unique_ptr
s instead of moving them, so I attempted to add my own move function to my
Deck
class, but I still get the error.

Here is a minimal example of the code in question (
Card
is just a dummy class, with no objects in it):

Deck.h:

#include "Card.h"
#include <vector>
#include <memory>

class Deck
{
public:
typedef std::unique_ptr<Card> cardPtr;

Deck();

Deck(Deck && other)
: mDeck(std::move(other.mDeck))
{
}

Deck& operator=(Deck other)
{
swap(*this, other);
return *this;
}

friend void swap(Deck& lhs, Deck& rhs);

void sortDeck();

private:
static bool compareCards(cardPtr A, cardPtr B);

private:
std::vector<cardPtr> mDeck;
};


Deck.cpp:

#include "Deck.h"
#include <algorithm>


Deck::Deck()
{
}

void swap(Deck& lhs, Deck& rhs)
{
using std::swap;
swap(lhs.mDeck, rhs.mDeck);
}


bool Deck::compareCards(cardPtr A, cardPtr B)
{
return true; //dummy- normally would have logic here
}

void Deck::sortDeck()
{
std::sort(mDeck.begin(), mDeck.end(), compareCards); //bug happens here
}


Any ideas about how to fix this? I'm sure I must be missing something fairly obvious, but I have been beating my head against this and googling it for a fair amount of time now, and could use some help.

Answer

Your compareCards function takes the unique_ptrs by value, this won't work as they are not copyable (the unique_ptr copy constructor is implicitly deleted due to the presence of move constructors, a copyable unique_ptr wouldn't be very unique would it?).

Change it to

bool compareCards(cardPtr const& A, cardPtr const& B);

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