c++ - 运行时检查失败 #0 - ESP 的值未在函数调用中正确保存

Question

我创建了一个简单的程序来演示我在使用多重继承的 Qt 应用程序中遇到的运行时错误。继承树如下所示:

QGraphicsItem (abstract)
      \
     QGraphicsLineItem      MyInterface (abstract)
                 \          /
                  \        /
                  MySubclass

代码如下:

/* main.cpp */
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsLineItem>

//simple interface with one pure virtual method
class MyInterface
{
public:
  virtual void myVirtualMethod() = 0;
};

//Multiple inheritance subclass, simply overrides the interface method
class MySubclass: public QGraphicsLineItem, public MyInterface
{
public:
  virtual void myVirtualMethod() { }
};

int main(int argc, char** argv)
{
  QApplication app(argc, argv); //init QApplication
  QGraphicsScene *scene = new QGraphicsScene(); //create scene

  scene->addItem(new MySubclass()); // add my subclass to the scene

  Q_FOREACH(QGraphicsItem *item, scene->items()) // should only have one item
  {
    MyInterface *mInterface = (MyInterface*)item; // cast as MyInterface
    mInterface->myVirtualMethod(); // <-- this causes the error
  }
  return 0;
}

调用我的接口(interface)方法时，在 visual studio 中调试会导致运行时错误:

    Run-Time Check Failure #0 - The value of ESP was not properly 
    saved across a function call.  This is usually a result of 
    calling a function declared with one calling convention with 
    a function pointer declared with a different calling convention.

知道问题出在哪里吗？

Answer 1

因为您使用的是多重继承，所以 vftable 指向预期为 MyInterface* 的指针实际上是指向 QGraphicsLineItem vftable.

dynamic_cast 会解决这个问题，因为它会返回正确的 vftable

MyInterface* mInterface = dynamic_cast<MyInterface*>(item);

一个简单的例子:

class A
{
public:
    virtual void foo() = 0;
};

class B
{
public:
    virtual void goo() {};
};

class C : public B, public A
{
public:
    virtual void foo() {}; 
};

//....

B* c = new C;                  // c  is at 0x00a97c78 
A* a = (A*)c;                  // a  is at 0x00a97c78 (vftable pointer of B) 
A* a1 = dynamic_cast<A*>(c);   // a1 is at 0x00a97c7c (vftable pointer of A)