使用dynamic_cast指向其他派生類對象

Question

我有以下情況。 有兩個基類：Base1，Base2和兩個派生類：派生sysCommandExecutor，它們派生如下：

#include <iostream>
using namespace std;

class Base1 { virtual void dummy() {} };
class Base2 { virtual void dumy() {} };
class Derived: virtual public Base1, public Base2
{ int a; };

class sysCommandExecutor : public Base2
{
public:
int b;
Base1 *ptr;
void func(void);
};

void sysCommandExecutor::func(void)
{
  Derived *d;
  d = dynamic_cast<Derived *>(ptr);
  if (d == NULL)
  std::cout << "This is NULL" << std::endl;
  else
  {
  // Call a function of Derived class
  }
}

int main () {
   try {
   sysCommandExecutor * sys =  new sysCommandExecutor;
   sys->func();
   return 0;
   }
}                                         

我想在func中調用“派生”類的此函數，但dynamic_cast失敗。 我無法在sysCommandExecutor類中創建該函數，因為那是其他人的代碼。 如何使sysCommandExecutor類中的ptr指針指向派生類對象？

提前致謝

Answer 1

您引用的是未初始化的指針ptr

如果我將main更改為：

int main () {
   sysCommandExecutor * sys =  new sysCommandExecutor;
   sys->ptr=new Derived;
   sys->func();
   delete dynamic_cast<Derived *>(sys->ptr);
   delete sys;
   return 0;

} 

有用

您也缺少虛擬dtor