如何在 C++ 中调用析构函数

Question

我试图在这里找到答案，但我没有找到任何工作。我这里有一个二十一点游戏。我的下一步是开始在游戏中添加资金余额并下注，但在此之前，我正在研究我的“再玩”选项。就目前而言，当玩家再次玩时，他们的手牌与上一轮相同。我相信我需要调用析构函数来删除当前的手牌和套牌，然后重新开始。不幸的是，我无法弄清楚如何清除手并从新的甲板开始。我试图在名为 play 的函数中调用这个析构函数。在这里，如果玩家说他们想再玩一次，我会删除手牌和套牌，然后在主界面中重建它们。但是我已经尝试过“deck.Deck::~Deck()”和“deck.~Deck()”，但都没有奏效。我会上传我所有的代码。如果有人有任何想法，请帮助我。我知道析构函数应该在超出范围时由编译器调用，但是如何在游戏仍在运行且主要仍在运行的情况下从新的手牌和套牌开始？感谢您的帮助。

这是我的头文件：

//blackjack.h A class to represent a deck of cards
#include <iostream>
#include <string>


class Card { 
  friend class Deck;
  private:
    int card_index; //card number 0 to 51
    Card(int index) { card_index = index; } //made this private so user can't say card at index 100..can use it because of friend class
  public:
    Card() { card_index = 52; }
    char suit() const;
    char value() const;
    std::string str() const;
    int getValue(std::string c);
};

class Deck {
  private:
    Card cards[52];
    int pos;
  public:
    Deck();
    ~Deck();
    Card deal() { return cards[pos++]; };
    void shuffle();
    int size() const { return 52 - pos; };
};

class Hand {
  friend class Deck;
  friend class Card;
  private:
    int handSize;
    int ctotal;
    Card myCards[52];

  public:   
    Hand() { handSize = 1; };
    ~Hand();
    Hand(int n) { handSize = n; };
    void dealFrom(Deck& d);
    void reveal();   
    int total();
    void hit(Deck& d);
};

std::ostream& operator<< (std::ostream& out, const Card& c);

这是我的实现文件：

//blackjack.cpp - Implementations of the Deck and Card classes
#include "blackjack.h"
#include <cstdlib>



char Card::suit() const {
  static char suits[] = { 'H', 'S', 'D', 'C' };
  //return card_index < 52 ? suits[card_index % 4] : 'X';
  return suits[card_index % 4];
}

char Card::value() const {
  static char values[] = 
    { '2', '3', '4', '5', '6', '7', '8', '9', 'T', 'J', 'Q', 'K', 'A' };
    //return card_index < 52 ? values[card_index / 4] : 'X';
    return values[card_index / 4];
}

std::string Card::str() const {
  std::string s;
  s += value();
  s += suit();
  return s;
}

Deck::Deck() {
  for (int i = 0; i < 52; i ++) {
    cards[i] = Card(i);
  }
  pos = 0;
}

void Deck::shuffle() {
  for (int i = 0; i < 52; i++) {
    int j = rand() % 52;
    Card tmp = cards[i];
    cards[i] = cards[j];
    cards[j] = tmp;
  }
  pos = 0;
}

std::ostream& operator<< (std::ostream& out, const Card& c) {
  out << c.str();
  return out;
}

int Card::getValue(std::string c) {
  char v = c[0];
  int val = v - '0';
  if (val > 9) {
    switch(v){
      case 'T':
      case 'J':
      case 'Q':
      case 'K':
        val = 10;
        break;
      case 'A':
         val = 11;
    }
  }
  return val;

}
void Hand::dealFrom(Deck& d) {
  for(int i = 0; i < handSize; i++)
      myCards[i] = d.deal();
}

void Hand::reveal(){ 
  for (int i = 0; i < handSize; i++) 
    std::cout << myCards[i] << " " << std::endl;
}

void Hand::hit(Deck& d) {
  int index = handSize;
  handSize++;
  myCards[index] = d.deal();

}

int Hand::total() {

  ctotal = 0; //reset card total

  for (int i = 0; i < handSize; i ++) {
    ctotal += myCards[i].getValue(myCards[i].str());
  }

  for (int i = 0; i < handSize; i ++) { //make ace 1 if over 21
    if ( (myCards[i].getValue(myCards[i].str()) == 11) && ctotal > 21 )
      ctotal = ctotal - 10;
  }

  return ctotal;

}

这是我的主要程序：

#include "blackjack.h"
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

void play(bool& quitGame, bool& quit, Deck& deck, Hand& d,Hand & p) { //function to play again?
  char ans;
  cout << "\nPlay Again? y or n" << endl;
  cin >> ans;
  if (ans == 'y' || ans == 'Y') {
    quitGame = false;
    quit = false;
    deck.Deck::~Deck(); //trying to delete the deck and hand objects before next game
    d.Hand::~Hand();
    p.Hand::~Hand();
    //deck.~Deck();
    //d.~Hand();
    //p.~Hand();

  } else if (ans == 'n' || ans == 'N')
    quitGame = true;
  else {
    cout << "Incorrect response." << endl;
    play(quitGame, quit, deck, d, p);
  }

}

void reveal(Hand& d, Hand& p) { //function to reveal the hand
  cout << "Your hand is: " << endl;
      p.reveal();
      cout << "Your total is: " << endl;
      cout << p.total() << endl;
      cout << endl;
      cout << "Dealer's hand is: " << endl;
      d.reveal();
      cout << "Dealer's total is: " << endl;
      cout << d.total() << endl;
}
void autoComplete(Hand& d, Hand& p, bool& quit, bool& quitGame, Deck& deck) { //function to check for blackjack and over 21
  if (p.total() == 21 && d.total() == 21) {
    cout << "You and dealer both hit blackjack. You tied." << endl;
    quit = true;
    play(quitGame, quit, deck, d, p);
  } else if(p.total() == 21) {
    cout << "Congratulations, you hit blackjack. You win!" << endl;
    quit = true;
    play(quitGame, quit, deck, d, p);
  } else if(d.total() == 21) {
    cout << "Sorry. Dealer hit blackjack. You lose." << endl;
    quit = true;
    play(quitGame, quit, deck, d, p);    
  } else if (p.total() > 21 && d.total() > 21) {
    cout << "You and dealer both passed 21. Game is a tie." << endl;
    quit = true;
    play(quitGame, quit, deck, d, p);
  } else if (p.total() > 21 && d.total() < 21) {
    cout << "You passed 21. You lose.";
    quit = true;
    play(quitGame, quit, deck, d, p);
  } else if (d.total() > 21 && p.total() < 21) {
    cout << "Dealer passed 21. You win.";
    quit = true;
    play(quitGame, quit, deck, d, p);
  }
}

int main() {
  srand(time(0));

  char response; // variable to hit or stand
  bool quit = false; //variable to end the current round
  bool quitGame = false; //variable to play game again

  while (quitGame == false) { //while the player wants to continue playing

    Deck deck; //create deck
    Hand p(2); //player's hand
    Hand d(2); //dealer's hand
    deck.shuffle(); //shuffle deck
    p.dealFrom(deck); //deal from deck
    d.dealFrom(deck);

    while (quit == false) { //while the round isn't over
      reveal(d, p); //reveal the cards
      autoComplete(d, p, quit, quitGame, deck); //check for blackjack and over 21


      if(p.total() < 21 && quit == false) { //if games not over and player is under 21
        cout << "Press 'h' to hit or 's' to stand." << endl;
        cin >> response; 
      }

      if (response == 'h') {
        cout << " " << endl;
        p.hit(deck);
        if (d.total() < 17) //if the dealer hasn't hit 17, dealer hits deck
          d.hit(deck);
      }
      if (response == 's') {
        cout << " " << endl;
        while (d.total() < 17){ //if the dealer hasn't hit 17, keep hitting deck
          d.hit(deck);
        }
        if (d.total() < 21 && p.total() < 21) {
          if (d.total() > p.total() && quit == false) { //if dealers total is higher than players total
            reveal(d, p);
            cout << "\nDealer wins!" << endl;
            quit = true;
            play(quitGame, quit, deck, d, p);
          } else if (p.total() > d.total() && quit == false) { //if players total is higher than dealers total
            reveal(d, p);
            cout << "\nYou win!" << endl;
            quit = true;
            play(quitGame, quit, deck, d, p);
          } else if (p.total() == d.total() && quit == false) { //if dealers total equals players total
            reveal(d, p);
            cout << "\nYou tied." << endl;
            quit = true;
            play(quitGame, quit, deck, d, p);
          }
        }
      } 
    }
  }    

  return 0;

}

Answer 1

语法：

Class obj;
obj.~Class();

将调用该对象的析构函数。然而，你应该不这样做。举个例子：

#include <cstdio>

class Foo {
public:
    Foo() {}
    ~Foo() {
        printf("Destroya\n");
        if (foo_m) delete foo_m;
    }
private:
    int* foo_m = new int(42);
};

int main() {
    Foo foo;
    foo.~Foo();
}

代码链接

从输出中可以看出，析构函数被调用了两次。第一次当我们手动“销毁”一个对象时，当它真正离开堆栈时又一次。

几乎从不手动调用析构函数。该对象不会消失，您只会破坏其状态并获得未定义的行为。您真正想要的可能是类似于clear()或reset()函数的东西来重新初始化状态。或者按照评论中的建议，您可以将分配一个默认对象移动到您已经存在的对象中以重置状态，而无需编写额外的功能。