c++ - 尝试将 std::sort() 与自定义对象一起使用

Question

我在网上查了一些教程。我已经在我的身上试过了，但问题是 std::sort()不执行任何操作!这是我的全部代码:

#include <string>
#include <iostream>
#include <iomanip>
#include <sstream> 
#include <algorithm>
#include <vector>
using namespace std;

#ifndef _card_h
#define _card_h

enum Suit {
    CLUBS, DIAMONDS, HEARTS, SPADES
};

enum Rank {
    TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN, JACK, QUEEN, KING, ACE
};

class Card {
    public:
        Card();
        Card(Rank, Suit);
        ~Card();
        Rank GetRank();
        Suit GetSuit();
        string ToString();
    private:
        Rank rank;
        Suit suit;
};
#endif

Card::Card() {
}

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

Card::~Card() {}

Rank Card::GetRank() {
    return rank;
}

Suit Card::GetSuit() {
    return suit;
}

string Card::ToString() {
    string cardName = "";
    switch (rank) {
        case TWO   : cardName += "2"; break;
        case THREE : cardName += "3"; break;
        case FOUR  : cardName += "4"; break;
        case FIVE  : cardName += "5"; break;
        case SIX   : cardName += "6"; break;
        case SEVEN : cardName += "7"; break;
        case EIGHT : cardName += "8"; break;
        case NINE  : cardName += "9"; break;
        case TEN   : cardName += "T"; break;
        case JACK  : cardName += "J"; break;
        case QUEEN : cardName += "Q"; break;
        case KING  : cardName += "K"; break;
        case ACE   : cardName += "A"; break;
    }
    switch (suit) {
        case CLUBS    : cardName += "C"; break;
        case DIAMONDS : cardName += "D"; break;
        case HEARTS   : cardName += "H"; break;
        case SPADES   : cardName += "S"; break;
    }
    return cardName;
}

#ifndef _cardcomparer_h
#define _cardcomparer_h

class CardComparer {  
    public:
        bool operator() (Card*, Card*);
    private:
        Card* firstCard;
        Card* secondCard;
};
#endif

bool CardComparer::operator() (Card* firstCard, Card* secondCard) {
    this->firstCard = firstCard;
    this->secondCard = secondCard;
    cout << "in Cardcompare! " << endl;
    if (firstCard->GetRank() == secondCard->GetRank()) {
        return firstCard->GetSuit() > secondCard->GetSuit();
    }
    else {
        return firstCard->GetRank() > secondCard->GetRank();
    }
}

#ifndef _hand_h
#define _hand_h
const int CARDS_IN_HAND = 5;
class Hand {
    public:
        Hand(int);
        ~Hand();
        void AddCard(Card*);
        string ToString();

    private:
        int cardCount;
        int playerID;
        vector<Card*> cards;

};
#endif

Hand::Hand(int playerID) {
    this->playerID = playerID;
    cards.reserve(CARDS_IN_HAND);
    cardCount = 0;
}

Hand::~Hand() {
    cards.clear();
}

void Hand::AddCard(Card* newCard) {
    cards[cardCount] = newCard;
    cardCount++;
    sort(cards.begin(), cards.end(),CardComparer());
}

string Hand::ToString() {
    stringstream playerCards;
    playerCards << "Player " << this->playerID << " -";
    for (int i = 0; i < cardCount; i++ ){
        playerCards << " " << cards[i]->ToString();
    }
    return playerCards.str();
}

int main() {
    vector<Hand*> hands;
    hands.reserve(1);
    hands[0] = new Hand(0);
    hands[0]->AddCard(new Card((Rank)4, (Suit)1));
    hands[0]->AddCard(new Card((Rank)8, (Suit)2));
    hands[0]->AddCard(new Card((Rank)5, (Suit)1));
    hands[0]->AddCard(new Card((Rank)2, (Suit)0));
    hands[0]->AddCard(new Card((Rank)7, (Suit)3));
    cout << hands[0]->ToString() << endl;
    return 0;
}

问题是第 133 行(sort(cards.begin(), cards.end(),CardComparer());)没有执行。无论我将其注释掉还是在结果中都没有改变，我什至在 93(cout << "in Cardcompare! " << endl;)上添加了额外的一行，如果它使用 bool，它会打印出一些东西。然而事实并非如此。我找不到问题出在哪里。这里有什么问题，我该如何解决？

Answer 1

问题是 vector 不知道您尝试在 AddCard 中添加卡片，或者更准确地说，您没有真的添加这些卡片，因为您确实不调用 push_back 而是简单地将指针放在内存中的某个位置。是的，由于调用 reserve，vector 拥有该内存，但它认为它是空的。因此 begin() 和 end() 给出了相同的迭代器并且 sort 正好对 0 个元素进行排序。

在您选择的教科书中查找有关 vector 和其他容器的章节。您不需要跟踪卡片的数量 (cardCount)，因为如果使用得当， vector 会为您完美地完成这项工作。