未解析的外部符号如何解决？抽象类-解网

问：

这是我的抽象类 Storestate.h：

#ifndef STORESTATE_H_
#define STORESTATE_H_

class Store;
class StoreState
{
public:
    virtual void Close(Store&);
    virtual void Open(Store&);
    virtual void Sell(Store&);
};

#endif

派生类头文件 ConcreteStateOpened.h：

#ifndef CONCRETESTATEOPENED_H_
#define CONCRETESTATEOPENED_H_
#include "StoreState.h"
#include "Store.h"

class ConcreteStateOpened : public StoreState
{
public:
    ConcreteStateOpened() {}
    void Open(Store&) override;
    void Close(Store&) override;
    void Sell(Store&) override;
};

#endif

Dervied 类 cpp 文件 ConcreteStateOpened.cpp：

#include "ConcreteStateOpened.h"
#include <iostream>

using namespace std;

void ConcreteStateOpened::Open(Store &store)
{
    cout << store.Name << " is already opened!" << endl;
}
void ConcreteStateOpened::Close(Store &store)
{
    store.State = ConcreteStateOpened();
}
void ConcreteStateOpened::Sell(Store &store)
{
    std::cout << "Sell Opened";
}

我不知道如何解决这个问题。我尝试删除覆盖关键字以及虚拟关键字。甚至删除定义等。我只是需要专业人士的帮助：，）

以下是未解决的外部符号错误：

1>ConcreteStateOpened.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Close(class Store &)" (?Close@StoreState@@UAEXAAVStore@@@Z)
1>Data.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Close(class Store &)" (?Close@StoreState@@UAEXAAVStore@@@Z)
1>StateStore.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Close(class Store &)" (?Close@StoreState@@UAEXAAVStore@@@Z)
1>ConcreteStateOpened.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Open(class Store &)" (?Open@StoreState@@UAEXAAVStore@@@Z)
1>Data.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Open(class Store &)" (?Open@StoreState@@UAEXAAVStore@@@Z)
1>StateStore.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Open(class Store &)" (?Open@StoreState@@UAEXAAVStore@@@Z)
1>ConcreteStateOpened.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Sell(class Store &)" (?Sell@StoreState@@UAEXAAVStore@@@Z)
1>Data.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Sell(class Store &)" (?Sell@StoreState@@UAEXAAVStore@@@Z)
1>StateStore.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall StoreState::Sell(class Store &)" (?Sell@StoreState@@UAEXAAVStore@@@Z)
1>D:\Local-Git-Repos\DesignPatterns\StateC++\StateStore\Debug\StateStore.exe : fatal error LNK1120: 3 unresolved externals

C++ 继承多态性抽象类未解析 - 外部

#ifndef CONCRETESTATEOPENED_H_
#define CONCRETESTATEOPENED_H_
#include "StoreState.h"
#include "Store.h"

class ConcreteStateOpened : public StoreState
{
public:
    ConcreteStateOpened() {}
    virtual void Open(Store&) override;
    virtual void Close(Store&) override;
    virtual void Sell(Store&) override;
};

#endif

#ifndef STORESTATE_H_
#define STORESTATE_H_

class Store;
class StoreState
{
public:
    virtual ~StoreState() = default;
    StoreState(const StoreState&) = delete;
    StoreState(StoreState&&) = delete;
    StoreState& operator=(const StoreState&) = delete;

    virtual void Close(Store&) = 0;
    virtual void Open(Store&) = 0;
    virtual void Sell(Store&) = 0;
protected:
    StoreState() = default; // prevent accidental creation
};

#endif

0赞 Vlad from Moscow 8/23/2021 #3

对于初学者来说，您提供的代码中没有抽象类，因为该类不包含纯虚函数。StoreState

来自 C++ 20 标准（11.7.3 抽象类）

2 虚函数被指定为纯虚函数，使用类中函数声明中的纯说明符（11.4）定义。[注意：这样的功能可能是继承的：见下文。尾注] 如果一个类至少有一个纯类，则该类是抽象类虚拟功能。[注意：抽象类只能用作其他类的基类;抽象类的任何对象都不能创建，但作为派生自它的类的子对象（6.2、11.4）除外。— 尾注] 纯虚函数只有在调用时才需要定义，或者好像使用（11.4.6），qualified-id 语法

您需要提供类中声明的虚函数的定义，或者使它们成为纯虚函数，例如StoreState

class StoreState
{
public:
    virtual void Close(Store&) = 0;
    virtual void Open(Store&) = 0;
    virtual void Sell(Store&) = 0;
};

即使一个函数被声明为纯虚函数，但如果需要，你可以提供它的定义（在它被声明为纯虚函数的类定义之外）。

请注意，当你有多态类时，你应该将析构函数也声明为虚拟的。例如

class StoreState
{
public:
    virtual ~StoreState() = default;

    virtual void Close(Store&) = 0;
    virtual void Open(Store&) = 0;
    virtual void Sell(Store&) = 0;
};

0赞 aschepler 8/23/2021 #4

你实际上不是抽象的。您已将、声明为具有定义的实际虚函数。要声明该类中没有定义的虚函数，请使用 “pure virtual” 语法。StoreStateCloseOpenSell= 0

此外，多态类类型的最佳做法是具有虚拟析构函数。根据五法则，当您声明析构函数时，请务必考虑复制/移动构造函数和复制/移动赋值。对于接口类，通常最好将其设置为不可复制和不可分配。

class StoreState
{
public:
    StoreState() = default;
    StoreState(const StoreState&) = delete;
    StoreState& operator=(const StoreState&) = delete;
    virtual ~StoreState() = default;

    virtual void Close(Store&) = 0;
    virtual void Open(Store&) = 0;
    virtual void Sell(Store&) = 0;
};

上一个：错误：C++ 中未解析的外部符号错误

下一个：c中用于用户定义函数的未解析外部符号

未解析的外部符号如何解决？抽象类

Unresolved External Symbol how to fix it? abstract class

评论

评论