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From: "P E Schoen" <paul@pstech-inc.com>
Newsgroups: comp.lang.pascal.delphi.misc
Subject: Strings and PChar (D4 Pro)
Date: Sat, 27 Aug 2016 05:39:10 -0400
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Xref: csiph.com comp.lang.pascal.delphi.misc:732

This is probably a very basic question, but I may have been improperly 
casting a string to PChar in some cases. For instance, I got the following 
code to work as shown:

====================================================
procedure TfmOrtDatabase.btBackupClick(Sender: TObject);
var       udfn: OrtData.TUserDataFile;
          S, dbFileName, saveFileName, dirName: String;
//          currDir: String;
          currDir: array[0..50] of Char;
begin
  if Application.MessageBox( 'Backup Database Files?',
         'Backup', MB_YESNO ) = ID_YES then begin //1
//    currDir := '01234567890123456789012345678901234567890123456789';
//    SetLength(currDir,50);
    GetCurrentDirectory(sizeof(currDir)+1, @currDir);
    dirName := GetSystemFolder(CSIDL_PERSONAL);
    dirName := dirName + '\Ortmaster';
    SelectDirectory(dirName, [sdAllowCreate,sdPerformCreate], 0);
//    SelectDirectory('Select Directory', dirName, dirName);
    S := FormatDateTime('yyyymmdd', Now);
    fmDBSaveDialog.InitialDir := dirName;
    for udfn := udfCust to udfTypes do begin //2
      dbFileName := ProgramDataFolder + '\' + 
OrtData.UserFileName[udfn]+'.dbf';
      fmDBSaveDialog.FileName := OrtData.UserFileName[udfn]+'.dbf';
      if not (fmDBSaveDialog.Execute) then exit;
      if (FileExists(dbFileName)) then begin //3
         saveFileName := fmDBSaveDialog.FileName + '-' + S;
         if not( CopyFile( pChar(dbFileName), PChar(saveFileName), FALSE ) ) 
then
            MessageDlg('File Copy Error', mtInformation, [mbOK], 0);;
      end; //-3
    end; //-2

    fmDBSaveDialog.InitialDir := dirName;
    dbFileName := 'Ortmaster' + '.rcf';
    fmDBSaveDialog.FileName := dbFileName;
    dbFileName := ProgramDataFolder + '\Ortmaster' + '.rcf';
    if not (fmDBSaveDialog.Execute) then exit;
    if (FileExists(dbFileName)) then begin //2
       saveFileName := fmDBSaveDialog.FileName + '-' + S;
       if not( CopyFile( pChar(dbFileName), pChar(saveFileName), FALSE ) ) 
then
          MessageDlg('File Copy Error', mtInformation, [mbOK], 0);;
    end; //-2
  SetCurrentDirectory(currDir);
  end; //-1
end;

=========================================================

If I used an uninitialized string, the GetCurrentDirectory() function 
failed, even when I initialized the string to a constant as shown. It's 
rather late, and maybe my brain is fogged, but it seems like there should be 
a better way to do this. It would be nice if there were a function like 
GetSystemFolder() that returns a string.

BTW, the SelectDirectory() function seems to be what I was searching for in 
a post from 7/20/15.

Also, I'm not sure why the current directory got changed by the function.

Thanks,

Paul