WriteRead Sample

The WriteRead.cpp creates a property set, writes a property, closes and reopens the property set, and reads back the property. This sample application creates the file "WriteRead.stg" in the current directory. It creates property sets in a structure storage file, but a one-line change causes it to create NTFS file system property sets.

//+===================================================================
//
// To build:
// cl /GX WriteRead.cpp
//
//+===================================================================


#define WIN32_LEAN_AND_MEAN
#define UNICODE
#define _UNICODE

#include <stdio.h>
#include <windows.h>
#include <ole2.h>

// Implicitly link ole32.dll
#pragma comment( lib, "ole32.lib" )


// From uuidgen.exe:
const FMTID fmtid = { /* d170df2e-1117-11d2-aa01-00805ffe11b8 */
 0xd170df2e,
 0x1117,
 0x11d2,
 {0xaa, 0x01, 0x00, 0x80, 0x5f, 0xfe, 0x11, 0xb8}
 };


EXTERN_C void wmain()
{
 HRESULT hr = S_OK;
 IPropertySetStorage *pPropSetStg = NULL;
 IPropertyStorage *pPropStg = NULL;
 WCHAR *pwszError = L"";
 PROPSPEC propspec; 
 PROPVARIANT propvarWrite; 
 PROPVARIANT propvarRead;

 try
 {

 // Create a file and a property set within it.

 hr = StgCreateStorageEx( L"WriteRead.stg",
 STGM_CREATE|STGM_SHARE_EXCLUSIVE|STGM_READWRITE,
 STGFMT_STORAGE,
 // STGFMT_STORAGE => Structured Storage 
 // property sets
 // STGFMT_FILE => NTFS file system 
 // property sets
 0, NULL, NULL,
 IID_IPropertySetStorage,
 reinterpret_cast<void**>(&pPropSetStg) );
 if( FAILED(hr) ) throw L"Failed StgCreateStorageEx";

 hr = pPropSetStg->Create( fmtid, NULL, PROPSETFLAG_DEFAULT, 
 STGM_CREATE|STGM_READWRITE|STGM_SHARE_EXCLUSIVE,
 &pPropStg );
 if( FAILED(hr) ) throw L"Failed IPropertySetStorage::Create";

 // Write a Unicode string property to the property set

 propspec.ulKind = PRSPEC_LPWSTR;
 propspec.lpwstr = L"Property Name";

 propvarWrite.vt = VT_LPWSTR;
 propvarWrite.pwszVal = L"Property Value";

 hr = pPropStg->WriteMultiple( 1, &propspec, &propvarWrite, 
 PID_FIRST_USABLE );
 if( FAILED(hr) ) 
 throw L"Failed IPropertyStorage::WriteMultiple";

 // Not required, but give the property set a friendly 
 // name.

 PROPID propidDictionary = PID_DICTIONARY;
 WCHAR *pwszFriendlyName = 
 L"Write/Read Properties Sample Property Set";
 hr = pPropStg->WritePropertyNames( 1, &propidDictionary, 
 &pwszFriendlyName );
 if( FAILED(hr) ) 
 throw L"Failed IPropertyStorage::WritePropertyNames";

 // Commit changes to the property set.

 hr = pPropStg->Commit(STGC_DEFAULT);
 if( FAILED(hr) ) 
 throw L"Failed IPropertyStorage::Commit";

 // Close and reopen everything.
 // By using the STGFMT_ANY flag in the StgOpenStorageEx call,
 // it does not matter if this is a Structured Storage 
 // property set or an NTFS file system property set 
 // (for more information see the StgCreateStorageEx 
 // call above).

 pPropStg->Release(); pPropStg = NULL;
 pPropSetStg->Release(); pPropSetStg = NULL;

 hr = StgOpenStorageEx( L"WriteRead.stg",
 STGM_READ|STGM_SHARE_DENY_WRITE,
 STGFMT_ANY,
 0, NULL, NULL, 
 IID_IPropertySetStorage,
 reinterpret_cast<void**>(&pPropSetStg) );
 if( FAILED(hr) ) 
 throw L"Failed StgOpenStorageEx";

 hr = pPropSetStg->Open( fmtid, STGM_READ|STGM_SHARE_EXCLUSIVE,
 &pPropStg );
 if( FAILED(hr) ) 
 throw L"Failed IPropertySetStorage::Open";

 // Read the property back and validate it

 hr = pPropStg->ReadMultiple( 1, &propspec, &propvarRead );
 if( FAILED(hr) ) 
 throw L"Failed IPropertyStorage::ReadMultiple";

 if( S_FALSE == hr )
 throw L"Property didn't exist after reopening the 
 property set";
 else if( propvarWrite.vt != propvarRead.vt )
 throw L"Property types didn't match after reopening the 
 property set";
 else if( 0 != wcscmp( propvarWrite.pwszVal, 
 propvarRead.pwszVal ))
 throw L"Property values didn't match after reopening the 
 property set";
 else
 wprintf( L"Success\n" );

 }
 catch( const WCHAR *pwszError )
 {
 wprintf( L"Error: %s (hr=%08x)\n", pwszError, hr );
 }

 PropVariantClear( &propvarRead );
 if( pPropStg ) pPropStg->Release();
 if( pPropSetStg ) pPropSetStg->Release();

}