Question

我正在尝试用c ++编写一个基本的gui库，我遇到了看似基本的继承问题。我在Component.h中有一个基类Component：

class Component
{
public:
    virtual void add(Component &c);
    virtual void remove(Component &c);
    virtual void setBounds(int x, int y, int width, int height);
    virtual void setLocation(int x, int y);
    virtual void setSize(int width, int height);
    virtual void setVisible(bool b);
};

我还在这里显示的相同标题中声明了一个子类框架

class Frame : public Component
{
private:
    char* ftitle;
    HWND* hwnd;

public:
    Frame();
    Frame(char* title);
    void add(Component &c);
    void remove(Component &c);
    void setBounds(int x, int y, int width, int height);
    void setLocation(int x, int y);
    void setSize(int width, int height);
    void setVisible(bool b);
    void setTitle(char* title);
};

我在另一个名为Frame.cpp的文件中实现了这个类函数

#include "Component.h"

Frame::Frame()
{
    Frame("");
}

Frame::Frame(char* title)
{
    ftitle = title;
    *hwnd = CreateWindow("static", title, WS_OVERLAPPEDWINDOW, 0, 0, 100, 100, NULL, NULL, GetModuleHandle(NULL), NULL);
}

void Frame::setVisible(bool visible)
{
    if(visible)
    {
        ShowWindow(*hwnd, SW_SHOW);
    }
    else
    {
        ShowWindow(*hwnd, SW_HIDE);
    }
}

void Frame::add(Component &c){}
void Frame::remove(Component &c){}
void Frame::setBounds(int x, int y, int width, int height){}
void Frame::setLocation(int x, int y){}
void Frame::setSize(int width, int height){}
void Frame::setTitle(char* title){}

然而，当我尝试编译和构建项目时，我得到了几个错误，如下所示

1>------ Build started: Project: GUI, Configuration: Debug Win32 ------
1>  Frame.cpp
1>  Generating Code...
1>  Compiling...
1>  Main.cpp
1>  Generating Code...
1>Frame.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Component::add(class Component &)" (?add@Component@@UAEXAAV1@@Z)
1>Frame.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Component::remove(class Component &)" (?remove@Component@@UAEXAAV1@@Z)
1>Frame.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Component::setBounds(int,int,int,int)" (?setBounds@Component@@UAEXHHHH@Z)
1>Frame.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Component::setLocation(int,int)" (?setLocation@Component@@UAEXHH@Z)
1>Frame.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Component::setSize(int,int)" (?setSize@Component@@UAEXHH@Z)
1>Frame.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Component::setVisible(bool)" (?setVisible@Component@@UAEX_N@Z)
1>C:\Users\Owner\Documents\Visual Studio 2012\Projects\GUI\Debug\GUI.exe : fatal error LNK1120: 6 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

链接器抱怨缺少Component类方法的实现，因为它们不是纯虚方法。您可以通过将它们变为纯虚拟来解决此问题：

virtual void add(Component &c) = 0;

等等。

或者，提供实施。

请注意，您还应该为Component提供虚拟析构函数。

在子类之外实现函数会导致未知错误

1 个答案: