c++ - 成员函数指针作为构造函数参数

Question

我有一个属性类，用于在类中设置 getter 和 setter 属性。它有效，但要使用它，我必须使用公共(public)变量设置属性，并在构造函数中调用 3 个方法，1 个函数用于设置类实例，1 个用于设置 setter，一个用于设置 getter。

class PropTest
{
private:
    int m_nCount;

    int getCount()
    {
        return m_nCount;
    }
    void setCount(int nCount)
    {
        m_nCount = nCount;
    }

public:
    PropTest()
    {
        Count.setObject(this);
        Count.setSetter(&PropTest::setCount);
        Count.setGetter(&PropTest::getCount);
    }

    Property<PropTest, int> Count = Property<PropTest, int>(PropertyPermission::READ | PropertyPermission::WRITE);
};

这很好用，但我正在尝试将其全部缩减为一行...

Property<PropTest, int> Count = Property<PropTest, int>(this, &PropTest::getCount, &PropTest::setCount, PropertyPermission::READ | PropertyPermission::WRITE);

但是当我将新的构造函数添加到类中并尝试编译时，我得到: error C2276: '&' : 对绑定(bind)成员函数表达式的非法操作

新的构造函数是:

template <class Class, typename Return> !!This template is for the whole class not the function. Just figured you needed to see it.

Property(Class* pObject, Return(Class::*pGetter)(), void (Class::*pSetter)(Return pValue), const int pPropertyPermission = PropertyPermission::READ | PropertyPermission::WRITE)

添加实例立即生效，但导致错误的是 getter 和 setter 参数。但是在 setGetter 和 setSetter 方法中使用相同的设置时编译和工作正常。

谢谢...

编辑

Property<PropTest, int> Count{ this, &PropTest::getCount, &PropTest::setCount, PropertyPermission::READ | PropertyPermission::WRITE };

是否是导致错误的行...

属性类-

static const enum PropertyPermission
{
    READ = (1 << 0),
    WRITE = (1 << 1)
};

template <class Class, typename Return>
class Property
{
private:
    Class* _object;
    Return(Class::*_getter)();
    void (Class::*_setter)(Return value);

public:
    Property(const int pPropertyPermission = PropertyPermission::READ | PropertyPermission::WRITE)
    {
        _getter = nullptr;
        _object = nullptr;
        _setter = nullptr;
        permission = pPropertyPermission;
    }
    Property(Class* pObject, const int pPropertyPermission = PropertyPermission::READ | PropertyPermission::WRITE)
    {
        _getter = nullptr;
        _object = pObject;
        _setter = nullptr;
        permission = pPropertyPermission;
    }
    Property(Class* pObject, Return(Class::*pGetter)(), void (Class::*pSetter)(Return pValue), const int pPropertyPermission = PropertyPermission::READ | PropertyPermission::WRITE)
    {
        _getter = nullptr;
        _object = pObject;
        _setter = nullptr;
        permission = pPropertyPermission;
    }

    operator Return()
    {
        //test for object and getter != null
        if (!(permission & PropertyPermission::READ))
    {
        //throw write only
    }
    return (_object->*_getter)();
    }

    Return operator =(const Return& pValue)
    {
        //test for object and setter != null
        if (!(permission & PropertyPermission::WRITE))
        {
            //throw read only
        }
        (_object->*_setter)(pValue);
        return pValue;
    }

    void setGetter(Return(Class::*pGetter)())
    {
        //test for object != null
        _getter = pGetter;
    }
    void setObject(Class* pObject)
    {
        _object = pObject;
    }
    void setSetter(void (Class::*pSetter)(Return pValue))
    {
        //test for object != null
        _setter = pSetter;
    }

    int permission;
};

测试-

int main(int pArgumentLength, char* pArguments[])
{
    int i = 5;
    int j = 0;
    PropTest* test = new PropTest();
    test->Count = i;
    j = test->Count;
    std::cout << test->Count << std::endl;
    std::cout << j << std::endl;
    delete test;
}

编辑

我使用 Visual Studio ... 当我打开 -Treat warnings as errors- 它编译但有一个异常:

Unhandled exception at 0x7445C9F5 in TestBed.exe: 0xC0000005: Access violation executing location 0x00000000.

有 2 个警告:

Warning 2   warning C4100: 'pSetter' : unreferenced formal parameter ...\testbed\program.cpp    58  1   TestBed

Warning 3   warning C4100: 'pGetter' : unreferenced formal parameter    ...\testbed\program.cpp 58  1   TestBed

第 58 行是构造函数:

Property(Class* pObject, Return(Class::*pGetter)(), void (Class::*pSetter)(Return pValue), const int pPropertyPermission = PropertyPermission::READ | PropertyPermission::WRITE)

解决方案

所以这一行导致了错误:

Property<PropTest, int> Count = Property<PropTest, int>(this, &PropTest::getCount, &PropTest::setCount, PropertyPermission::READ | PropertyPermission::WRITE);

使用它代替编译并运行良好:(Kerrek SB)

Property<PropTest, int> Count{ this, &PropTest::getCount, &PropTest::setCount, PropertyPermission::READ | PropertyPermission::WRITE };

但我不知道为什么...

感谢大家的回复。

Answer 1

在您的 Property 类实现中，您永远不会设置您的指针成员值:

Property(Class* pObject, Return(Class::*pGetter)(), void (Class::*pSetter)(Return pValue), const int pPropertyPermission = PropertyPermission::READ | PropertyPermission::WRITE)
{
    _getter = nullptr;
    _object = pObject;
    _setter = nullptr;
    permission = pPropertyPermission;
}

应该改为:

Property(Class* pObject, Return(Class::*pGetter)(), void (Class::*pSetter)(Return pValue), const int pPropertyPermission = PropertyPermission::READ | PropertyPermission::WRITE)
{
    _getter = pGetter;
    _object = pObject;
    _setter = pSetter;
    permission = pPropertyPermission;
}