delphi - 如何将 IStream 加载到 TMemoryStream

Question

如何使用 TComInterface<IStream> 对象并将其读入 TMemoryStream？我可以采用 TComInterface<IStream> 并将其用作 TStream* 以某种方式使用 TMemoryStream LoadFromStream 调用吗？

Answer 1

一种方法是Read()将IStream数据放入缓冲区，然后Write()将其放入TMemoryStream，例如：

TComInterface<IStream> pIStrm;
TMemoryStream *pMStrm;

...

STATSTG stat = {0};
OleCheck(pIStrm->Stat(&stat, STATFLAG_NONAME));

LARGE_INTEGER li;
li.QuadPart = 0;
ULARGE_INTEGER ul;
OleCheck(pIStrm->Seek(li, STREAM_SEEK_CUR, &ul));
unsigned __int64 ulPos = ul.QuadPart;

BYTE buffer[1024];
while (ulPos < stat.cbSize.QuadPart)
{
    ULONG ulRead;
    OleCheck(pIStrm->Read(buffer, min(stat.cbSize.QuadPart - ulPos, sizeof(buffer)), &ulRead));
    pMStrm->WriteBuffer(buffer, ulRead);
    ulPos += ulRead;
}

...

另一种选择是编写一个TStream访问内部的派生类IStream（类似于 RTL 的TStreamAdapter类如何包装 aTStream以便它可以作为 a 传递IStream），例如：

class TIStreamWrapper : public TStream
{
private:
    TComInterface<IStream> pIStrm;

protected:
    virtual __int64 __fastcall GetSize();
    virtual void __fastcall SetSize(const __int64 NewSize);

public:
    __fastcall TIStreamWrapper(IStream *Strm);
    virtual int __fastcall Read(void *Buffer, int Count);
    virtual int __fastcall Write(const void *Buffer, int Count);
    virtual __int64 __fastcall Seek(const __int64 Offset, TSeekOrigin Origin);
};

__fastcall TIStreamWrapper::TIStreamWrapper(IStream *Strm)
    : pIStrm(Strm, true)
{
}

__int64 __fastcall TIStreamWrapper::GetSize()
{
    STATSTG stat = {0};
    OleCheck(pIStrm->Stat(&stat, STATFLAG_NONAME));
    return stat.cbSize.QuadPart;
}

void __fastcall TIStreamWrapper::SetSize(const __int64 NewSize)
{
    ULARGE_INTEGER ul;
    ul.QuadPart = NewSize;
    OleCheck(pIStrm->SetSize(ul));
}

int __fastcall TIStreamWrapper::Read(void *Buffer, int Count)
{
    ULONG ulRead;
    OleCheck(pIStrm->Read(Buffer, Count, &ulRead));
    return ulRead;
}

int __fastcall TIStreamWrapper::Write(const void *Buffer, int Count)
{
    ULONG ulWritten;
    OleCheck(pIStrm->Write(Buffer, Count, &ulWritten));
    return ulWritten;
}

static const DWORD IStreamSeekOrigin[] = {STREAM_SEEK_SET, STREAM_SEEK_CUR, STREAM_SEEK_END};

__int64 __fastcall TIStreamWrapper::Seek(const __int64 Offset, TSeekOrigin Origin)
{
    LARGE_INTEGER li;
    li.QuadPart = Offset;
    ULARGE_INTEGER ul;
    OleCheck(pIStrm->Seek(li, IStreamSeekOrigin[Origin], &ul));
    return ul.QuadPart;
}

TComInterface<IStream> pIStrm;
TMemoryStream *pMStrm;
...
TIStreamWrapper *pWrapper = new TIStreamWrapper(pIStrm);
try
{
    pMStrm->LoadFromStream(pWrapper);
    // or: pMStrm->CopyFrom(pWrapper, 0);
}
__finally
{
    delete pWrapper;
}

...