[英]“pure virtual function call” error on Debug ONLY
以下“事件”代码段显示“纯虚拟函数调用”错误。 但是,如标题中所述,仅在DEBUG上部署时才会发生。 让我感到奇怪的是,为什么它在RELEASE上可以完美运行,为什么甚至崩溃(在DEBUG上)。 或者,您可以在此处查看代码段。
#include <list>
#include <iostream>
#include <algorithm>
// use base class to resolve the problem of how to put into collection objects of different types
template <typename TPropertyType>
struct PropertyChangedDelegateBase
{
virtual ~PropertyChangedDelegateBase(){};
virtual void operator()(const TPropertyType& t) = 0;
};
template <typename THandlerOwner, typename TPropertyType>
struct PropertyChangedDelegate : public PropertyChangedDelegateBase<TPropertyType>
{
THandlerOwner* pHandlerOwner_;
typedef void (THandlerOwner::*TPropertyChangeHandler)(const TPropertyType&);
TPropertyChangeHandler handler_;
public:
PropertyChangedDelegate(THandlerOwner* pHandlerOwner, TPropertyChangeHandler handler) :
pHandlerOwner_(pHandlerOwner), handler_(handler){}
void operator()(const TPropertyType& t)
{
(pHandlerOwner_->*handler_)(t);
}
};
template<typename TPropertyType>
class PropertyChangedEvent
{
public:
virtual ~PropertyChangedEvent(){};
void add(PropertyChangedDelegateBase<TPropertyType>* const d)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = std::find(observers_.begin(), observers_.end(), d);
if(it != observers_.end())
throw std::runtime_error("Observer already registered");
observers_.push_back(d);
}
void remove(PropertyChangedDelegateBase<TPropertyType>* const d)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = std::find(observers_.begin(), observers_.end(), d);
if(it != observers_.end())
observers_.remove(d);
}
// notify
void operator()(const TPropertyType& newValue)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = observers_.begin();
for(; it != observers_.end(); ++it)
{
(*it)->operator()(newValue);
}
}
protected:
std::list<PropertyChangedDelegateBase<TPropertyType>* const> observers_;
};
class PropertyOwner
{
int property1_;
float property2_;
public:
PropertyChangedEvent<int> property1ChangedEvent;
PropertyChangedEvent<float> property2ChangedEvent;
PropertyOwner() :
property1_(0),
property2_(0.0f)
{}
int property1() const {return property1_;}
void property1(int n)
{
if(property1_ != n)
{
property1_ = n;
property1ChangedEvent(n);
}
}
float property2() const {return property2_;}
void property2(float n)
{
if(property2_ != n)
{
property2_ = n;
property2ChangedEvent(n);
}
}
};
struct PropertyObserver
{
void OnPropertyChanged(const int& newValue)
{
std::cout << "PropertyObserver::OnPropertyChanged() -> new value is: " << newValue << std::endl;
}
};
int _tmain(int argc, _TCHAR* argv[])
{
PropertyOwner propertyOwner;
PropertyObserver propertyObserver;
// register observers
PropertyChangedDelegate<PropertyObserver, int> delegate(&propertyObserver, &PropertyObserver::OnPropertyChanged);
propertyOwner.property1ChangedEvent.add(&delegate); // Ok!
propertyOwner.property1ChangedEvent.add(&PropertyChangedDelegate<PropertyObserver, int>(&propertyObserver, &PropertyObserver::OnPropertyChanged)); // Error: Virtual pure function call (Debug only)
propertyOwner.property1(1);
return getchar();
}
我会认为该错误使用不当,并且该问题更有可能与第二个代表所处的范围有关。 加上在外面声明它更容易阅读。
传递通过堆栈而不是通过引用创建的对象通常是一个坏主意。 项目声明超出范围后,通常会忘记该对象。
普遍的问题是,您绑定到一个临时文件,该临时文件将被销毁,因此具有空的vtable
并且当对属性的更改进行调用时,它当然会生成纯虚拟调用。 如果为基类添加一个dtor,则很容易观察到:
#include <list>
#include <iostream>
#include <algorithm>
// use base class to resolve the problem of how to put into collection objects of different types
template <typename TPropertyType>
struct PropertyChangedDelegateBase
{
virtual ~PropertyChangedDelegateBase(){};
virtual void operator()(const TPropertyType& t) = 0;
};
template <typename THandlerOwner, typename TPropertyType>
struct PropertyChangedDelegate : public PropertyChangedDelegateBase<TPropertyType>
{
THandlerOwner* pHandlerOwner_;
typedef void (THandlerOwner::*TPropertyChangeHandler)(const TPropertyType&);
TPropertyChangeHandler handler_;
public:
PropertyChangedDelegate(THandlerOwner* pHandlerOwner, TPropertyChangeHandler handler) :
pHandlerOwner_(pHandlerOwner), handler_(handler)
{
std::cout << "0x" << std::hex << this << " created!" << std::endl;
}
void operator()(const TPropertyType& t)
{
(pHandlerOwner_->*handler_)(t);
}
~PropertyChangedDelegate()
{
std::cout << "0x" << std::hex << this << " destroyed!" << std::endl;
}
};
template<typename TPropertyType>
class PropertyChangedEvent
{
public:
virtual ~PropertyChangedEvent(){};
void add(PropertyChangedDelegateBase<TPropertyType>* const d)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = std::find(observers_.begin(), observers_.end(), d);
if (it != observers_.end())
throw std::runtime_error("Observer already registered");
observers_.push_back(d);
}
void remove(PropertyChangedDelegateBase<TPropertyType>* const d)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = std::find(observers_.begin(), observers_.end(), d);
if (it != observers_.end())
observers_.remove(d);
}
// notify
void operator()(const TPropertyType& newValue)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = observers_.begin();
for (; it != observers_.end(); ++it)
{
std::cout << "Invoking 0x" << std::hex << *it << std::endl;
(*it)->operator()(newValue);
}
}
protected:
std::list<PropertyChangedDelegateBase<TPropertyType>* const> observers_;
};
class PropertyOwner
{
int property1_;
float property2_;
public:
PropertyChangedEvent<int> property1ChangedEvent;
PropertyChangedEvent<float> property2ChangedEvent;
PropertyOwner() :
property1_(0),
property2_(0.0f)
{}
int property1() const { return property1_; }
void property1(int n)
{
if (property1_ != n)
{
property1_ = n;
property1ChangedEvent(n);
}
}
float property2() const { return property2_; }
void property2(float n)
{
if (property2_ != n)
{
property2_ = n;
property2ChangedEvent(n);
}
}
};
struct PropertyObserver
{
void OnPropertyChanged(const int& newValue)
{
std::cout << "PropertyObserver::OnPropertyChanged() -> new value is: " << newValue << std::endl;
}
};
int main(int argc, char* argv[])
{
PropertyOwner propertyOwner;
PropertyObserver propertyObserver;
// register observers
PropertyChangedDelegate<PropertyObserver, int> delegate(&propertyObserver, &PropertyObserver::OnPropertyChanged);
propertyOwner.property1ChangedEvent.add(&delegate); // Ok!
propertyOwner.property1ChangedEvent.add(&PropertyChangedDelegate<PropertyObserver, int>(&propertyObserver, &PropertyObserver::OnPropertyChanged)); // Error: Virtual pure function call (Debug only)
propertyOwner.property1(1);
return getchar();
}
基本上,您只是遇到未定义的行为-两种情况下对象都被破坏,但是在Release中, vtable
没有被破坏,所以您可以通过。
这个:
propertyOwner.property1ChangedEvent.add(
&PropertyChangedDelegate<PropertyObserver, int>(
&propertyObserver,
&PropertyObserver::OnPropertyChanged)
);
您正在捕获一个指向临时对象PropertyChangedDelegate<PropertyObserver, int>
的指针。 一旦函数调用结束并且指向临时对象的指针就指向该对象的指针无效。 取消引用此指针是未定义的行为。
在您的程序中,内存所有权关系至关重要,您应该仔细考虑它们。 您需要手动确保所有指针都超出依赖它们的对象:
PropertyChangedDelegate<PropertyObserver, int> delegate2 = {
&propertyObserver,
&PropertyObserver::OnPropertyChanged
};
propertyOwner.property1ChangedEvent.add(&delegate2);
或使用智能指针( std::unique_ptr<>
, std::shared_ptr<>
)。
另一个错误:
符合C ++ 11的编译器不应允许您这样做:
std::list<PropertyChangedDelegateBase<TPropertyType>* const> observers_;
我在Visual Studio 2015中遇到的错误是:
C ++标准禁止容器const元素,因为分配器的格式不正确。
请参阅: C ++ 11是否允许vector<const T>
?
奖金:
您的C ++样式看起来已经过时了。 您可能要尝试自动类型推断:
for(auto it = observers_.begin(); it != observers_.end(); ++it)
{
(*it)->operator()(newValue);
}
或者更好的是,范围为循环:
for(auto observer : observers)
{
observer(newValue);
}
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