Microsoft KB Archive/135682

= PRB: Drag and Drop with TYMED_FILE Runs Out of File Handles =

Article ID: 135682

Article Last Modified on 12/8/2003

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APPLIES TO


 * Microsoft Visual C++ 1.5 Professional Edition
 * Microsoft Visual C++ 1.51
 * Microsoft Visual C++ 1.52 Professional Edition
 * Microsoft Visual C++ 1.52 Professional Edition
 * Microsoft Visual C++ 2.0 Professional Edition
 * Microsoft Visual C++ 2.1
 * Microsoft Visual C++ 2.2
 * Microsoft Visual C++ 4.0 Standard Edition

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This article was previously published under Q135682



SYMPTOMS
Calling Open on the CFile pointer returned from COleDataObject::GetFileData may return EMFILE. Usually, this will happen after repeated drag and drop operations and subsequent calls to GetFileData. It is also possible to see memory leaks upon termination of the application, specifically, of memory blocks the size of a CFile object.



CAUSE
The documentation for COleDataObject::GetFileData does not mention that the returned CFile pointer is owned by the caller. Therefore, it is the responsibility of the caller to call Close on or simply delete that pointer. The reason for the EMFILE return code is that the files opened in the drag and drop operation are never closed and therefore the system handles are exhausted. Memory leaks are caused by not deleting the CFile objects that were dynamically allocated by GetFileData.

The documentation for COleDataObject::GetFileData provided with Visual C++ 4.0 has been improved. It mentions the fact that it is the responsibility of the caller to delete the returned CFile object, thereby closing the file.



RESOLUTION
Remember to delete the CFile pointer returned from GetFileData after using it.

Sample Code
The following OnDrop function definition illustrates the correct cleanup after using the CFile pointer returned from GetFileData. BOOL CMyView::OnDrop(COleDataObject* pDataObject, DROPEFFECT de,                       CPoint point) {      CFile * pFile = pDataObject->GetFileData(CF_HGLOBAL); char lpBuf[100];

if (NULL != pFile) pFile->Read(lpBuf, 100); .      .       .       // Make sure to delete the CFile * delete pFile; return TRUE; }

Additional query words: cfile delete stgm_hfile tymed_file

Keywords: kbdragdrop kbprb KB135682

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