我如何初始化一个CARRAY＆LT的默认值; CClass *＆GT;用空CARRAY函数参数？ [英] How can I initialize the default value of a CArray<CClass*> function parameter with an empty CArray?

问题描述

我知道我可以用的std ::矢量更好地做到这一点，但我搞乱的应用，已经有一堆 CARRAY <的对很多相关的功能/ code>参数......而此刻我不会改变他们！

I know I could do this better with std::vector, but the application I am messing with, has already a bunch of CArray parameters on a lot of related functions ... and I will not change them all at the moment!

我只是想定义一个空的 CARRAY＆LT; CClass *＆GT; - 阵列的指针以 CClass ，所以问题的不能在 CClass 构造函数 - 作为函数参数的默认值

I simply want to define an empty CArray<CClass*> — array of pointers to CClass, so the problem can not be on the CClass constructor — as the default value of a function parameter.

方法1

如果我尝试的赋值运算符的做出来，的默认的构造函数的：

If I try to do it with assignment operator and default constructor:

void Function(CArray<CClass*> parameter = CArray<CClass*>());

我得到的错误：

1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\atlmfc\include\afxTempl.h(262): error C2248: 'CObject::CObject' : cannot access private member declared in class 'CObject'
1>          C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\atlmfc\include\afx.h(535) : see declaration of 'CObject::CObject'
1>          C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\atlmfc\include\afx.h(510) : see declaration of 'CObject'
1>          This diagnostic occurred in the compiler generated function 'CArray<TYPE>::CArray(const CArray<TYPE> &)'
1>          with
1>          [
1>              TYPE=CClass *
1>          ]

方法2

我也试过用的拷贝构造函数的：

void Function(CArray<Class*> parameter(CArray<CClass*>()));

我得到了错误：

 >File.cpp(line X): error C2664: 'FunctionClass::Function' : cannot convert parameter 1 from 'CArray<TYPE>' to 'CArray<TYPE> (__cdecl *)(CArray<TYPE> (__cdecl *)(void))'
1>          with
1>          [
1>              TYPE=CClass*
1>          ]
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

• 行X：包含一个呼叫提供的参数功能，如下所示： pFunctionClass-＆GT;功能（参数）;


• line X: contains a call supplying the parameter to Function, as shown: pFunctionClass->Function(parameter);

1> CFunctionClass.cpp（行Y）：错误C2511：无效CFunctionClass ::功能（CARRAY）'：重载成员函数不是在'CShoePlaceDoc发现
1>
1> [
1> TYPE = CClass *
1>]
1> FunctionClass.h（A线）：见CFunctionClass

1>CFunctionClass.cpp(line Y): error C2511: 'void CFunctionClass::Function(CArray)' : overloaded member function not found in 'CShoePlaceDoc' 1> with 1> [ 1> TYPE=CClass* 1> ] 1> FunctionClass.h(line A) : see declaration of 'CFunctionClass'



• 线Y包含功能实施的头，如图所示：`无效CFunctionClass ::功能（CARRAY参数）


• line Y contains the Function implementation header, as shown: `void CFunctionClass::Function(CArray parameter)

1> File.cpp（线Z）：错误C2660：'CClassFunction ::功能'：函数不接受0参数

1>File.cpp(line Z): error C2660: 'CClassFunction::Function' : function does not take 0 arguments



• 行Z：包含功能呼叫而不提供它的参数，如下所示： pClassFunction-＆GT;功能（）;


• line Z: contains a call to Functionwithout supplying it parameters, as shown: pClassFunction->Function();

该方法没有工作，但它朝着的结论得到了它的方式：这是不可能的使用拷贝构造为函数参数指定一个默认值

The approach didn't work, but it got its way towards a conclusion: It is not possible to use a copy-constructor for assigning a default value for a function parameter.

方法3

如果我试图用的的λ的：

void Function(CArray<CClass*> parameter = [] () -> CArray<CClass*>{ return CArray<CClass*> (); } );

，那么我会得到这两个错误的多个输出：

, then I will get multiple outputs of these two errors:

1>FunctionClass.h(line A): error C2440: 'default argument' : cannot convert from '`anonymous-namespace'::<lambda2>' to 'CArray<TYPE>'
1>          with
1>          [
1>              TYPE=CClass*
1>          ]
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>FunctionClass.h(line B): fatal error C1903: unable to recover from previous error(s); stopping compilation



• A线：方法声明


• B线：收} 的 FunctionClass 包含类功能法


• line A: method declaration
• line B: closing } of FunctionClass class that contains Function method

问题的原产地

问题的根源似乎是一个事实，即 CARRAY 是的CObject 直接派生的类，该声明赋值运算符为​​私有

The root cause of the problem seems to be the fact that CArray is a class directly derived from CObject, which declares the assignment operator as private:

class AFX_NOVTABLE CObject
{
//...
private:
    CObject(const CObject& objectSrc);              // no implementation
    void operator=(const CObject& objectSrc);       // no implementation
//...
}

那么，如何可以提供一个空数组作为参数的默认值？

So, how can I supply an empty array as default value for the parameter?

推荐答案

通过这个声明

void Function(CArray<CClass*> parameter /*...*/);

您不能。调用此函数将调用的CObject 的私人拷贝构造函数，你已经注意到了。

You can't. Calling this function will invoke the private copy constructor of CObject as you have noticed.

你可以做什么，是添加静态CARRAY℃的对象; CClass *＆GT; 在你的类和对它的引用初始化函数。这样，这将是空的（只要你不填充...）的，你可以执行的 .IsEmpty（） 检查就可以了。

What you could do, is to add a object of static CArray<CClass*> in your class and initialize the function with a reference to it. This way it will be empty (as long as you do not populate it...) and you can perform a .IsEmpty() check on it.

private:
    static CArray<CClass*> myObj;
//...
void Function(CArray<CClass*> &parameter = myObj);

或者，它初始化为0，这样，您只需通过如果（参数）或如果（NULL ==参数）。

void Function(CArray<CClass*> *parameter = NULL);

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