Pointer to a C++ array of 'hat' handles

Question

Hi,

I'm trying to store a series of WriteOnlyArray objects:

WriteOnlyArray<unsigned char,1U>^* pMessages=new WriteOnlyArray<unsigned char,1U>^[10];

The compiler throws a "array of handles is not allowed" error.

I've also been trying to store these on a std:queue using ->push with no success... I think these two problems are related.

Why isn't an array of handles allowed, and how to store an array of WriteOnlyArray s?

Answer 1

Why don't you create an Array of WriteOnlyArray?

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http://blog.voidnish.com

Answer 2

I bet it is due to ^ pointers needing reference counting support and plain C++ arrays not being ref counting friendly.

Answer 3

Hi Todd2010,

From the MSDN documentation, we find these statement: “C++/CX supports authoring function parameters whose type is a read/write array (Platform::Array) or a write-only array (Platform::WriteOnlyArray). You can't define a WriteOnlyArray array, but you can declare a function parameter type as WriteOnlyArray so that the Windows Runtime can efficiently pass an Array by reference.”  For more information about defining and declaring WriteOnlyArray in C++/CX, please refer to this page: http://msdn.microsoft.com/en-us/library/hh700105(v=vs.110).aspx.

The following code fragment declares a function whose first parameter is a WriteOnlyArray<T>. The function is called by using an Array<T> object even though the function parameter type is WriteOnlyArray<T>:

using namespace Platform;

void MyFunc2(WriteOnlyArray<int>^ a, int* actual) {

    *actual = 0;

    if (ai->Length > 2) {

        a[0] = 0;

        a[1] = 1;

        *actual = 2;

    }

};

int main() {

    int used = 0;

    auto ai = ref new Array<int>(5);

    MyFunc2(ai, &used); // Array<T>^ has an implicit conversion to WriteOnlyArray<T>^

    return used;

}

Best regards,

Jesse

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Jesse Jiang [MSFT]
MSDN Community Support | Feedback to us

Answer 4

Hi Jesse,

Thanks for the reply, but this is not related to my question.  However, you are right that you can't explicitly declare a WriteOnlyArray.

I receive the same error if I try to declare an array of "Array".

Likewise, the std::queue->push method refuses to take either an Array or WriteOnlyArray as a type... my question is 'why'?

Thanks.

Answer 5

Hi Todd2010,

I have tried the following lines. These codes can be compiled successfully:

	Array<unsigned char>^ chararray;
	chararray=ref new Array<unsigned char>(10);
	queue<unsigned char>* q= new queue<unsigned char>;
	q->push(chararray[0]);

While the complication may be fail if the type of the queue element is Array or WriteOnlyArray. Please refer to the following codes:

	Array<unsigned char>^ chararray=ref new Array<unsigned char>(3);
	queue<Array<unsigned char>^>* qa= new queue<Array<unsigned char>^>;
	qa->push(chararray);//error C2664

	queue<WriteOnlyArray<int>^>* qw=new queue<WriteOnlyArray<int>^>;
	auto ai = ref new Array<int>(10);
	qw->push(ai);//error C2664

I hope this reply is helpful to you.
Best regards,

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Helen Zhao [MSFT]
MSDN Community Support | Feedback to us