从另一个类模块引用在 main 中创建的类的实例

问题描述

我正在研究一种需要两副牌的扑克变体。出于统计原因，重要的是在洗牌两副牌时使用通用的随机数生成器。为了测试，我有一个小的 main，我在其中创建了一个随机数生成器的实例和两个甲板的实例。我用语句“extern classRNG Random”引用了 classDeck 中的实例“Random”。

一切编译正常，但我收到链接器错误“Deck.obj : error LNK2001: unresolved external symbol "class classRNG Random" (?Random@@3VclassRNG@@A)。”如果我在 classDeck 中创建实例 Random 而不是在 main 中，一切都可以编译和链接，但当然这将为每个甲板创建一个单独的随机数生成器。

显然我忽略了一些东西。

有很多代码要处理，但我认为错误是由 Deck.cpp 中的函数“Shuffle”造成的，靠近 Deck.cpp 的末尾。那就是我有语句“extern classRNG Random”。注释掉“RawDeck[i].SortParam = Random.RNGGet()”行消除了错误。

这是RNG.h的代码：

#ifndef RNG_H 
#define RNG_H 

class classRNG
{
private:
    static unsigned long long Seed;

public:   
    classRNG();   // Default constructor;
    classRNG(unsigned long long ullSeed); // Constructor with initial seed
    unsigned long long RNGGet();  //Get a random number
};
#endif

RNG.cpp：

#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <stdbool.h>
#include "RNG.h"

using namespace std;

const unsigned long long T1 = 60LL,T2 = 59LL;

classRNG::classRNG()   // Default constructor
{
int i;

Seed = 3;

for (i=0; i<7*T1; i++)      //Step thru some numbers to stabilize
{
    RNGGet();
}
};

classRNG::classRNG(unsigned long long ullSeed) // Constructor with initial seed
{
const unsigned long long Mask1 = powl(2LL,T1);
const unsigned long long Mask = Mask1 - 2LL;

int i;

Seed = ullSeed % Mask;
for (i=0; i<7*T1; i++)      //Step over trivial numbers
{
    RNGGet();
}
};

// This method is used to obtain a random number.  It returns an unsigned Long Long.
unsigned long long classRNG::RNGGet()
{
const long long Test1 = powl(2LL,T1-1LL);
const long long Test2 = powl(2LL,T2-1LL);
const unsigned long long Mask1 = powl(2LL,T1);
const unsigned long long Mask = Mask1 - 2LL;
const unsigned long long Taps = Test1 | Test2;
const unsigned long long Scram = 0x693474786E579bd % Mask;

unsigned long long Test;

Test = Seed & Taps;
Seed = (Seed << 1) & Mask;
if (Test == Test1 | Test == Test2){
    Seed = Seed | 1LL;
}
return Seed * Scram;
};

unsigned long long classRNG::Seed = 3;

甲板.h：

#ifndef DECK_H
#define DECK_H

#include "struct_defs.h"

class classDeck
{
private:
    static int NextCard;    // Pointer to next card in the deck 
    static bool Ready;  // Indicates that deck is not dirty
    static structSortCard RawDeck[53];  // Stores the raw card value (1-52) with a sort parameter

    bool SortDeck(int Plow,int Phi);   // Used in Shuffle
    void SwapCards(int P1,int P2);     // Used in SortDeck

public:
    classDeck();  //Constructor;
    bool InitializeDeck();
    bool Shuffle();
    structCardDef GetCard();
    bool DeckReady ();
};
#endif

Deck.cpp：

#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <stdbool.h>
#include "RNG.h"
#include "struct_defs.h"    // Data structures
#include "Deck.h"

using namespace std;

/* 
This type manages the card deck.  No data are directly exposed.  It provides the following methods:
- InitializeDeck.   Restores deck to unsorted state. (Probably never use this)
- Shuffle.          Returns True when complete.
- GetCard.          Returns the next card as Class classCardDef.
- DeckReady.        Returns True if the deck is shuffled and not dirty. 
*/

int classDeck::NextCard = 1;
bool classDeck::Ready = false;
structSortCard classDeck::RawDeck[] = {0};

classDeck::classDeck()  //Constructor
{
InitializeDeck();
};


bool classDeck::SortDeck(int Plow,int Phi)
{
int Pivot,P1,P2,P3,i;

Ready = false;

// Check for trivial cases
if ((Phi - Plow) < 2)   // Nothing to sort
{
    return true;
}
if (((Phi - Plow) == 2) && RawDeck[Plow].SortParam > RawDeck[Phi].SortParam)    // Only two - easy peasy
{
    SwapCards(Phi,Plow);
    return true;
}

// Set Pivot to last element
Pivot = Phi;
P3 = 0;

// Search for an element larger than the pivot,and set P1 to that
for (P1 = Plow; P1 < Pivot; P1++)
{
    if(RawDeck[P1].SortParam > RawDeck[Pivot].SortParam)    // Found a large number
    {
        // Search from P1+1 to Pivot-1 to find an element smaller than the pivot and set P2 to that
    for (P2 = P1+1; P2 < Pivot; P2++)
        {
            if(RawDeck[P2].SortParam < RawDeck[Pivot].SortParam)    // Found a small number
            {
                // Swap elements at P1 & P2
                SwapCards(P1,P2);
                P3 = P1;    // Remember leftmost large card
                break;
            }
        }
        if (P2 >= Pivot)   // Reached the pivot without finding another small card
        {
            break;
        }
    }
}

// Move Pivot to P3
if (P3 > 0) // There's at least one large card
{
    SwapCards(P3,Pivot);  // The Pivot is now at P3
}

// Split into two parts,and iterate any part with more than one element
Ready = SortDeck(Plow,P3 - 1) && SortDeck(P3 + 1,Phi);
return Ready;
};


void classDeck::SwapCards(int P1,int P2)
{
structSortCard Temp;

Temp.Value  = RawDeck[P1].Value;
Temp.SortParam = RawDeck[P1].SortParam;

RawDeck[P1].Value = RawDeck[P2].Value;
RawDeck[P1].SortParam = RawDeck[P2].SortParam;

RawDeck[P2].Value = Temp.Value;
RawDeck[P2].SortParam = Temp.SortParam;
};



bool classDeck::InitializeDeck()
{
int i;

Ready = false;
for (i = 1; i <= 52; i++)
{
    RawDeck[i].Value = i;
}
Ready = Shuffle();
return Ready;
};


bool classDeck::Shuffle()
{
int i;
extern classRNG Random;

Ready = false;
for (i = 1; i <= 52;i++)
{
    RawDeck[i].SortParam = Random.RNGGet();
}

// Sort the deck
Ready = SortDeck(1,52);
return Ready;
};


structCardDef classDeck::GetCard()
{
structCardDef NewCard;
int Card;

Ready = false;
Card = RawDeck[NextCard++].Value;
NewCard.Card = Card % 13 + 1;
NewCard.Suit = Card / 13 + 1;
return NewCard;
};


bool classDeck::DeckReady ()
{
return Ready;
};

最后，main.cpp

#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <stdbool.h>
#include "RNG.h"
#include "struct_defs.h"
#include "Deck.h"

using namespace std;

int main()
{
unsigned long long X;
classRNG Random;    // Create an instance of classRNG
X = Random.RNGGet();

// Create two decks
classDeck Deck[2];

结构体“structSortCard”在“struct_defs.h”中定义为：

struct structSortCard
{
public:
    int Value;
    unsigned long long SortParam;
};

我尝试了很多方法都无济于事。

解决方法

classRNG Random 是 main 的局部变量 - 它不是全局变量，因此在 extern 中的 classDeck::Shuffle 调用中不可见。使用 extern 共享变量有点奇怪 - 为什么不让 Shuffle 接受 classRNG* 参数，以便您可以将相同的 classRNG 传递给每个实例（或者您如果您愿意，可以在构造函数中传递它）。或者，您也可以使 RNG 成为 classDeck 的静态成员，这样套牌将负责构建一个在所有实例之间共享的 classRNG。

本声明

extern classRNG Random;

在全局命名空间中声明（但未定义）变量 Random。

这个声明同时在main中定义了变量Random

int main()
{
unsigned long long X;
classRNG Random;    // Create an instance of classRNG
//...

声明一个局部变量，在 main 的块作用域之外不可见。

因此在全局命名空间中声明的变量 Random 仍然未定义。

您可以将局部变量 Random 的声明（不带存储说明符 extern）移到函数 main 之前。在这种情况下，此声明将是在全局命名空间中声明的变量 Random 的定义。

另一种方法是在类 classRNG 中创建类型为 classDeck 的（静态）数据成员。

c++extern linker-errors

从另一个类模块引用在 main 中创建的类的实例

问题描述

解决方法

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