Microsoft KB Archive/141921

= HOWTO: How to Support Two File Extensions per MFC Document Type =

Article ID: 141921

Article Last Modified on 12/7/2006

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APPLIES TO

 Microsoft Foundation Class Library 4.2, when used with:  Microsoft Visual C++ 1.0 Professional Edition

 Microsoft Visual C++ 1.5 Professional Edition

 Microsoft Visual C++ 1.51

 Microsoft Visual C++ 1.52 Professional Edition</li></ul>

 Microsoft Visual C++ 2.0 Professional Edition</li></ul>

 Microsoft Visual C++ 2.1</li></ul>

 Microsoft Visual C++ 2.2</li></ul>

 Microsoft Visual C++ 4.0 Standard Edition</li></ul> </li></ul>

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This article was previously published under Q141921

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SUMMARY
Applications built with the Microsoft Foundation Classes (MFC) document or view architecture have at most one file extension associated with each document type. This default file extension, if specified, is stored in the document template string stored in the string table.

It is often useful to associate two file extensions with a given document type. This article describes a technique you can use to allow two file extensions to be stored in the document template string. Through class derivation and function overrides, it is possible to associate both file extensions with the document template.

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Step-by-Step Procedure
Use the following steps to associate two file extensions with a single document type in either SDI or MDI applications.

<ol>  Modify the string table entry so that it contains two file extensions. The two extensions are entered into the filterExt field separated by a semicolon (for example, .aaa;.bbb). The document template string may look similar to this: <pre class="fixed_text">  \nExts\nExts\nFiles (*.aaa; *.bbb)\n.aaa;.bbb\nExts.Doc\nExts Doc. </li>  Derive a class from CMultiDocTemplate for MDI applications, or CSingleDocTemplate for SDI applications. Add this class to your project, and use it when creating the document templates in your InitInstance function. You will need to create a constructor that simply calls the base class constructor. CMyMultiDocTemplate::CMyMultiDocTemplate(     UINT nIDResource, CRuntimeClass* pDocClass,      CRuntimeClass* pFrameClass, CRuntimeClass* pViewClass ) : CMultiDocTemplate(nIDResource, pDocClass, pFrameClass, pViewClass) { };                   </li>  Override the GetDocString function in your class derived from CMultiDocTemplate or CSingleDocTemplate in step 2. BOOL CMyMultiDocTemplate::GetDocString(CString& rString,                           enum DocStringIndex i) const {       CString strTemp,strLeft,strRight; int nFindPos; AfxExtractSubString(strTemp, m_strDocStrings, (int)i);

if(i == CDocTemplate::filterExt) { nFindPos=strTemp.Find(';'); if(-1 != nFindPos) { //string contains two extensions strLeft=strTemp.Left(nFindPos+1); strRight=strTemp.Right(lstrlen((const           char*)strTemp)-nFindPos-1); strTemp=strLeft+strRight; }       }    rString = strTemp; return TRUE; }                   </li>  Override CMyMultiDocTemplate::MatchDocType so that both file extensions are recognized when a file is opened. CDocTemplate::Confidence CMyMultiDocTemplate::MatchDocType(const       char* pszPathName, CDocument*& rpDocMatch) {       ASSERT(pszPathName != NULL); rpDocMatch = NULL;

// go through all documents POSITION pos = GetFirstDocPosition; while (pos != NULL) {          CDocument* pDoc = GetNextDoc(pos); if (pDoc->GetPathName == pszPathName) { // already open rpDocMatch = pDoc; return yesAlreadyOpen; }       }  // end while

// see if it matches either suffix CString strFilterExt; if (GetDocString(strFilterExt, CDocTemplate::filterExt) &&         !strFilterExt.IsEmpty) {          // see if extension matches ASSERT(strFilterExt[0] == '.'); CString ext1,ext2; int nDot = CString(pszPathName).ReverseFind('.'); const char* pszDot = nDot < 0 ? NULL : pszPathName + nDot;

int nSemi = strFilterExt.Find(';'); if(-1 != nSemi)  { // string contains two extensions ext1=strFilterExt.Left(nSemi); ext2=strFilterExt.Mid(nSemi+2); // check for a match against either extension if (nDot >= 0 && (lstrcmpi(pszPathName+nDot, ext1) == 0 || lstrcmpi(pszPathName+nDot,ext2) ==0)) return yesAttemptNative; // extension matches }          else { // string contains a single extension if (nDot >= 0 && (lstrcmpi(pszPathName+nDot,                strFilterExt)==0)) return yesAttemptNative; // extension matches }       }        return yesAttemptForeign; //unknown document type }                   </li>  To make Save and Save As function correctly, override the DoSave function in your CDocument-derived class. Simply cut and paste the MFC implementation of CDocument::DoSave from Mfc\Src\Doccore.cpp into your derived class.

Replace these lines: // append the default suffix if there is one CString strExt; if (pTemplate->GetDocString(strExt, CDocTemplate::filterExt) &&           !strExt.IsEmpty) {          ASSERT(strExt[0] == '.'); newName += strExt; } with these lines: // append the default suffix if there is one CString strExt; if (pTemplate->GetDocString(strExt, CDocTemplate::filterExt) &&           !strExt.IsEmpty) {         ASSERT(strExt[0] == '.');

int nSemi;                      //added if(nSemi = strExt.Find(';'));   //added strExt = strExt.Left(nSemi);    //added

newName += strExt; } The three added lines of code return the first extension by default when Save As is processed for a document type that has two extensions specified in its document string. The user must type over this extension if a file is to be saved with the second extension specified in the document string.

You will also need to replace the following lines of code: CATCH_ALL(e) {     TRACE0("Warning: failed to delete file after failed SaveAs.\n"); DELETE_EXCEPTION(e); } with: CATCH_ALL(e) {     TRACE0("Warning: failed to delete file after failed SaveAs.\n"); e->Delete;    //modified } This is necessary because the DELETE_EXCEPTION macro is undefined in this context. </li> (16-bit Editions Only) Use Class Wizard to provide OnFileSave and OnFileSaveAs command handlers in your derived document class. This is necessary because in the 16-bit versions of Visual C++, the DoSave function is not virtual. Simply cut and paste the contents of the base class versions of both functions from Mfc\Src\Doccore.cpp into your command handlers. The resulting functions call the local copy of DoSave rather than the base class version. It may be necessary to add #include "io.h" to your project to provide a definition for the _access function.</li></ol>

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