C ++ Visual Studio 2015：非标准语法；使用“＆”创建指向成员的指针

卡h

#pragma once
#include <string>
#include "Rank.h"
#include "Suit.h"
using namespace std;

/**
 * 
 */
class MEMORYWARS_API Card
{
public:
    Card(Rank, Suit);
    string toString() const;
    ~Card();
private:
    Rank rank;
    Suit suit;
};

卡

#include "MemoryWars.h"
#include "Card.h"

Card::Card(Rank rank, Suit suit)
{
    this->rank = rank;
    this->suit = suit;
}

string Card::toString() const
{
    string s = "Hellow there";
    return s;
}

Card::~Card()
{
}

错误

error C3867: 'Card::toString': non-standard syntax; use '&' to create a pointer to member

Deck.h

#pragma once
#include "Card.h"
#include "vector"
class MEMORYWARS_API Deck
{
public:
    Deck();
    ~Deck();
private:
    std::vector<Card> deck;
};

Deck.cpp

#include "MemoryWars.h"
#include "Deck.h"
#include <EngineGlobals.h>
#include <Runtime/Engine/Classes/Engine/Engine.h>
Deck::Deck()
    : deck(52)
{
    int cc = 0;
    for (int i = 0; i < 4; i++)
    {
        for (int j = 0; j < 13; j++)
        {
            Rank rank = static_cast<Rank>(j);
            Suit suit = static_cast<Suit>(i);
            deck[cc] = Card(rank, suit);
            cc++;
        }
    }
    string st = deck[2].toString;
    GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Red, FString::Printf(TEXT("Some variable values: x: %s"), st));
}

Deck::~Deck()
{
}

我主要是具有Java经验的C ++新手，我一直在努力解决此错误。

我正在尝试测试Card :: toString方法，但是每次我从deck.cpp调用它时，都会收到错误消息。