具有虚函数的类，当从QObject派生时，导致链接错误

问题描述

以下是工作正常的代码

  class HttpService {
 public： 
 virtual〜HttpService（）; // implements in .cpp 
 protected：
 HttpService（struct MHD_Connection * conn）{} 
}; 
 class HttpFileService：public HttpService 
 {
 public：
 virtual〜HttpFileService（）; // implements in .cpp 
 protected：
 HttpFileService（struct MHD_Connection * conn）：HttpService（conn）{} 
}; 
  

现在，当我使 HttpService 类 QObject ，如下所示：

  #include< QObject> // change＃1 
 class HttpService：public QObject {// change＃2 
 Q_OBJECT // change＃3 
 public：
 virtual〜HttpService（）; 
 protected：
 HttpService（struct MHD_Connection * conn）{} 
}; 
 
 class HttpFileService：public HttpService {
 Q_OBJECT // change＃4 
 public：
 virtual〜HttpFileService（）; 
 protected：
 HttpFileService（struct MHD_Connection * conn）：HttpService（conn）{} 
}; 
  

我遇到以下链接错误：

 架构x86_64的未定义符号：
vtable for HttpService，引用自：
 HttpService ::〜httpservice.o中的HttpService（）
  

更改 HttpService 的构造函数不会帮助

 显式HttpService（QObject * parent = 0）：QObject（parent）
  pre> 
 
解决方案
强制运行qmake，看看是否有效。
 
Following is the code that works fine
class HttpService {
public:
    virtual ~HttpService(); // implemented in .cpp
protected:
    HttpService(struct MHD_Connection *conn) {}
};
class HttpFileService : public HttpService
{
public:
    virtual ~HttpFileService() ; // implemented in .cpp
protected:
    HttpFileService(struct MHD_Connection *conn) : HttpService(conn) {}
};
Now, when I make HttpService a derived class of QObject, like below:
#include <QObject>                      // change #1
class HttpService  : public QObject {   // change #2
    Q_OBJECT                            // change #3
public:
    virtual ~HttpService();
protected:
    HttpService(struct MHD_Connection *conn) {}
};

class HttpFileService : public HttpService {
    Q_OBJECT                            // change #4
public:
    virtual ~HttpFileService() ;
protected:
    HttpFileService(struct MHD_Connection *conn) : HttpService(conn) {}
};
I encounter the following linking error:
Undefined symbols for architecture x86_64:
  "vtable for HttpService", referenced from:
      HttpService::~HttpService()in httpservice.o
Changing HttpService's constructor to the following doesn't help either
explicit HttpService(QObject *parent = 0) : QObject(parent)
 解决方案 
Force running qmake and see if it works.
                        
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