pstream.h

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//------------------------------------------------------------------------------
// File: PStream.h
//
// Desc: DirectShow base classes - defines a class for persistent properties
//       of filters.
//
// Copyright (c) 1992-2001 Microsoft Corporation.  All rights reserved.
//------------------------------------------------------------------------------


#ifndef __PSTREAM__
#define __PSTREAM__

// Base class for persistent properties of filters
// (i.e. filter properties in saved graphs)

// The simplest way to use this is:
// 1. Arrange for your filter to inherit this class
// 2. Implement in your class WriteToStream and ReadFromStream
//    These will override the "do nothing" functions here.
// 3. Change your NonDelegatingQueryInterface to handle IPersistStream
// 4. Implement SizeMax to return the number of bytes of data you save.
//    If you save UNICODE data, don't forget a char is 2 bytes.
// 5. Whenever your data changes, call SetDirty()
//
// At some point you may decide to alter, or extend the format of your data.
// At that point you will wish that you had a version number in all the old
// saved graphs, so that you can tell, when you read them, whether they
// represent the old or new form.  To assist you in this, this class
// writes and reads a version number.
// When it writes, it calls GetSoftwareVersion()  to enquire what version
// of the software we have at the moment.  (In effect this is a version number
// of the data layout in the file).  It writes this as the first thing in the data.
// If you want to change the version, implement (override) GetSoftwareVersion().
// It reads this from the file into mPS_dwFileVersion before calling ReadFromStream,
// so in ReadFromStream you can check mPS_dwFileVersion to see if you are reading
// an old version file.
// Normally you should accept files whose version is no newer than the software
// version that's reading them.


// CPersistStream
//
// Implements IPersistStream.
// See 'OLE Programmers Reference (Vol 1):Structured Storage Overview' for
// more implementation information.
class CPersistStream : public IPersistStream {
    private:

        // Internal state:

    protected:
        DWORD     mPS_dwFileVersion;         // version number of file (being read)
        BOOL      mPS_fDirty;

    public:

        // IPersistStream methods

        STDMETHODIMP IsDirty()
            {return (mPS_fDirty ? S_OK : S_FALSE);}  // note FALSE means clean
        STDMETHODIMP Load(LPSTREAM pStm);
        STDMETHODIMP Save(LPSTREAM pStm, BOOL fClearDirty);
        STDMETHODIMP GetSizeMax(__out ULARGE_INTEGER * pcbSize)
                         // Allow 24 bytes for version.
                         { pcbSize->QuadPart = 12*sizeof(WCHAR)+SizeMax(); return NOERROR; }

        // implementation

        CPersistStream(IUnknown *punk, __inout HRESULT *phr);
        ~CPersistStream();

        HRESULT SetDirty(BOOL fDirty)
            { mPS_fDirty = fDirty; return NOERROR;}


        // override to reveal IPersist & IPersistStream
        // STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void **ppv);

        // --- IPersist ---

        // You must override this to provide your own class id
        STDMETHODIMP GetClassID(__out CLSID *pClsid) PURE;

        // overrideable if you want
        // file version number.  Override it if you ever change format
        virtual DWORD GetSoftwareVersion(void) { return 0; }


        //=========================================================================
        // OVERRIDE THESE to read and write your data
        // OVERRIDE THESE to read and write your data
        // OVERRIDE THESE to read and write your data

        virtual int SizeMax() {return 0;}
        virtual HRESULT WriteToStream(IStream *pStream);
        virtual HRESULT ReadFromStream(IStream *pStream);
        //=========================================================================

    private:

};


// --- Useful helpers ---


// Writes an int to an IStream as UNICODE.
STDAPI WriteInt(IStream *pIStream, int n);

// inverse of WriteInt
STDAPI_(int) ReadInt(IStream *pIStream, __out HRESULT &hr);

#endif // __PSTREAM__