c++ - 如何在 C++ 中将 char* 缓冲区包装在 WinRT IBuffer 中

Question

我想实现一个包装 char* 缓冲区的 C++ WinRT IBuffer，因此我可以将它与接受 IBuffer^ 参数的 WinRT WriteAsync/ReadAsync 操作一起使用。

编辑1（澄清）

我想避免数据复制。

Answer 1

主要从http://jeremiahmorrill.wordpress.com/2012/05/11/http-winrt-client-for-c/复制，但适用于直接包装我自己的字节[]：

NativeBuffer.h：

#pragma once

#include <wrl.h>
#include <wrl/implements.h>
#include <windows.storage.streams.h>
#include <robuffer.h>
#include <vector>

// todo: namespace

class NativeBuffer : 
    public Microsoft::WRL::RuntimeClass<Microsoft::WRL::RuntimeClassFlags<Microsoft::WRL::RuntimeClassType::WinRtClassicComMix>,
    ABI::Windows::Storage::Streams::IBuffer,
    Windows::Storage::Streams::IBufferByteAccess>
{
public:
    virtual ~NativeBuffer()
    {
    }

    STDMETHODIMP RuntimeClassInitialize(byte *buffer, UINT totalSize)
    {
        m_length = totalSize;
        m_buffer = buffer;

        return S_OK;
    }

    STDMETHODIMP Buffer(byte **value)
    {
        *value = m_buffer;

        return S_OK;
    }

    STDMETHODIMP get_Capacity(UINT32 *value)
    {
        *value = m_length;

        return S_OK;
    }

    STDMETHODIMP get_Length(UINT32 *value)
    {
        *value = m_length;

        return S_OK;
    }

    STDMETHODIMP put_Length(UINT32 value)
    {
        m_length = value;

        return S_OK;
    }

private:
    UINT32 m_length;
    byte *m_buffer;
};

创建 IBuffer：

Streams::IBuffer ^CreateNativeBuffer(LPVOID lpBuffer, DWORD nNumberOfBytes)
{
    Microsoft::WRL::ComPtr<NativeBuffer> nativeBuffer;
    Microsoft::WRL::Details::MakeAndInitialize<NativeBuffer>(&nativeBuffer, (byte *)lpBuffer, nNumberOfBytes);
    auto iinspectable = (IInspectable *)reinterpret_cast<IInspectable *>(nativeBuffer.Get());
    Streams::IBuffer ^buffer = reinterpret_cast<Streams::IBuffer ^>(iinspectable);

    return buffer;
}

以及读取数据的调用（lpBuffer 是 byte[]）：

Streams::IBuffer ^buffer = CreateNativeBuffer(lpBuffer, nNumberOfbytes);
create_task(randomAccessStream->ReadAsync(buffer, (unsigned int)nNumberOfBytesToRead, Streams::InputStreamOptions::None)).wait();

我不太确定 ComPtr 是否需要一些清理，因此欢迎提出有关内存管理的任何建议。

Answer 2

这应该有效：

// Windows::Storage::Streams::DataWriter
// Windows::Storage::Streams::IBuffer
// BYTE = unsigned char (could be char too)
BYTE input[1024] {};

DataWriter ^writer = ref new DataWriter();
writer->WriteBytes(Platform::ArrayReference<BYTE>(input, sizeof(input));
IBuffer ^buffer = writer->DetachBuffer();