Question

我试图在c ++上使用属性来代替太多的setter，而getter函数在数据类中有很多成员变量。

有两个属性类。第一个具有固定的setter和getter函数，默认设置为get。第二个支持使用其类的自定义setter和getter函数。下面是代码

template <class T>
class Property
{
    T data;
public:
    // access with function call syntax
    Property() : data() { }
    T operator()() const
    {
        return data;
    }
    T operator()( T const & value)
    {
        data = value;
        return data;
    }
    // access with get()/set() syntax
    T get() const
    {
        return data;
    }
    T set( T const & value )
    {
        data = value;
        return data;
    }

    // access with '=' sign
    operator T() const
    {
        return data;
    }
    T operator = ( T const & value )
    {
        data = value;
        return data;
    }

    typedef T value_type; // might be useful for template deductions
};



// a read-write property which invokes user-defined functions
template <class T, class Object, T(Object::*real_getter)(), T(Object::*real_setter)(T const &) >
class RWProperty
{
    Object * my_object;
public:
    // this function must be called by the containing class, normally in a
    // constructor, to initialize the RWProperty so it knows where its
    // real implementation code can be found
    void operator () ( Object * obj )
    {
        my_object = obj;
    }

    // function call syntax
    T operator()() const
    {
        return (my_object->*real_getter)();
    }
    T operator()( T const & value )
    {
        return (my_object->*real_setter)( value );
    }

    // get/set syntax
    T get() const
    {
        return (my_object->*real_getter)();
    }
    T set( T const & value )
    {
        return (my_object->*real_setter)( value );
    }

    // access with '=' sign
    operator T() const
    {
        return (my_object->*real_getter)();
    }
    T operator = ( T const & value )
    {
        return (my_object->*real_setter)( value );
    }

    typedef T value_type; // might be useful for template deductions
};

并且我在将OptionSet类放入项目代码之前测试这些属性

#include <QString>

class OptionSet
{
public:
    explicit OptionSet() {}

    Property<QString> m_MeshMode;

    RWProperty<uint, OptionSet, &getNumberOfVbo, &setNumberOfVbo> uNumberOfVbo; 
    // this causes problems

protected:

private:
    Property<uint> m_uNumberOfVbo;

    uint setNumberOfVbo(const uint& rVboCount)
    {
        // something to do here
        return m_uNumberOfVbo(rVboCount);
    }
    uint getNumberOfVbo() const
    {
        return m_uNumberOfVbo();
    }

};

但是在使用RWProperty时，即使我传递了模板的4个参数，比如成员类型，类类型有setter和getter函数，getter函数指针，setter函数指针按顺序，它说

＆＃34;模板参数数量错误（3，应为4）：   RWProperty＆lt; uint，OptionSet，＆amp; getNumberOfVbo，＆amp; setNumberOfVbo＆gt;   uNumberOfVbo＆＃34;

＆＃34;提供＆＃39;模板＆lt; class T，类Object，   T（Object :: * real_getter）（），T（Object :: * real_setter）（const T＆amp;）＆gt;类   RWProperty：类RWProperty＆＃34;

我想我在模板中传递参数时做错了。

有谁知道发生了什么事？

Answer 1

您的代码中有三个错误：

首先，要获取成员函数的地址，您需要包含类名：

public String executeScalarCommandString(String conString, OdbcCommand command)
        {
            //starting stopwatch here
            String result = "";
            // remember we have already a connection which already open
            // so we dont have to create new connection
/* we dont need this :: using (OdbcConnection connection = new OdbcConnection(conString))*/
            {
                try
                {
 // i'll assume the connection already on command object
                    //command.Connection = connection;
                    command.CommandType = CommandType.Text;
                    //connection.Open();
                    object obj = command.ExecuteScalar();
                    if (obj != null && DBNull.Value != obj)
                        result = obj.ToString();
                }
                catch (Exception ex)
                {
                    System.Windows.Forms.MessageBox.Show(ex.ToString());
                }
                //stop and restart stopwatch here. Avg elapsed time: 10 ms
            }
            //stop stopwatch here. Avg elapsed time: 76 ms
            return result;
        }

其次，要形成指向RWProperty<uint, OptionSet , &OptionSet::getNumberOfVbo // ~~~~~~~~~~~^ , &OptionSet::setNumberOfVbo> uNumberOfVbo; // ~~~~~~~~~~~^限定成员函数的指针，需要在该指针的声明中附加const关键字：

const

最后，T (Object::*real_getter)() const // ~~~~^ to match 'uint getNumberOfVbo() const'内的OptionSet本身是不完整的类型。除非首先声明该成员的声明，否则您不能引用其成员。这基本上意味着您需要在OptionSet内对声明进行重新排序，以便{/ 1}}和OptionSet来之前声明setNumberOfVbo数据成员：

getNumberOfVbo

错误的模板参数数量（3，应为4）

1 个答案: