Programmatically-Check-If-File-is-In-Use-Delphi-Code


            Title: Programmatically Check If File is In Use - Delphi Code
Tip submitted by Peter Barnard
The IsFileInUse Delphi function will return true if the file is locked for exclusive access. False is returned if the file does not exist.
Code "flow":
Two things need to be checked here: A) Is the file a READ-ONLY file? and B) Is the file in use?
The main point of the excercise is to check the files attributes for the READ-ONLY flag before doing the check for "in-use". If the file is READ-ONLY then offer the user the option to remove the READ-ONLY attribute so that processing can continue.
If the user wishes to remove the READ-ONLY attribute, the files attributes are cleared (set to NORMAL which is an exclusive attribute), and then whatever other attributes are restored.
 uses StrUtils;
 
 function IsFileInUse(fName : string) : boolean;
 var
 HFileRes : HFILE;
 Res: string[6];
 
 function CheckAttributes(FileNam: string; CheckAttr: string): Boolean;
 var
 fa: Integer;
 begin
 fa := GetFileAttributes(PChar(FileNam)) ;
 Res := '';
 
 if (fa and FILE_ATTRIBUTE_NORMAL) 0 then
 begin
 Result := False;
 Exit;
 end;
 
 if (fa and FILE_ATTRIBUTE_ARCHIVE) 0 then
 Res := Res + 'A';
 if (fa and FILE_ATTRIBUTE_COMPRESSED) 0 then
 Res := Res + 'C';
 if (fa and FILE_ATTRIBUTE_DIRECTORY) 0 then
 Res := Res + 'D';
 if (fa and FILE_ATTRIBUTE_HIDDEN) 0 then
 Res := Res + 'H';
 if (fa and FILE_ATTRIBUTE_READONLY) 0 then
 Res := Res + 'R';
 if (fa and FILE_ATTRIBUTE_SYSTEM) 0 then
 Res := Res + 'S';
 
 Result := AnsiContainsText(Res, CheckAttr) ;
 end; (*CheckAttributes*)
 
 procedure SetAttr(fName: string) ;
 var
 Attr: Integer;
 begin
 Attr := 0;
 if AnsiContainsText(Res, 'A') then
 Attr := Attr + FILE_ATTRIBUTE_ARCHIVE;
 if AnsiContainsText(Res, 'C') then
 Attr := Attr + FILE_ATTRIBUTE_COMPRESSED;
 if AnsiContainsText(Res, 'D') then
 Attr := Attr + FILE_ATTRIBUTE_DIRECTORY;
 if AnsiContainsText(Res, 'H') then
 Attr := Attr + FILE_ATTRIBUTE_HIDDEN;
 if AnsiContainsText(Res, 'S') then
 Attr := Attr + FILE_ATTRIBUTE_SYSTEM;
 
 SetFileAttributes(PChar(fName), Attr) ;
 end; (*SetAttr*)
 begin //IsFileInUse
 if CheckAttributes(fName, 'R') then
 begin
 Result := False;
 
 if not FileExists(fName) then exit;
 
 if MessageDlg(ExtractFileName(fName) + ' is a READ-ONLY file.' + #13#10 + 'Do you wish to clear the READ-ONLY flag???', mtConfirmation, [mbYes, mbNo], 0) = mrNo then
 beginb
 Result := True;
 Exit;
 end;
 end;
 
 SetFileAttributes(PChar(fName), FILE_ATTRIBUTE_NORMAL) ;
 
 SetAttr(fName) ;
 
 HFileRes := CreateFile(pchar(fName), GENERIC_READ or GENERIC_WRITE, 0, nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0) ;
 Result := (HFileRes = INVALID_HANDLE_VALUE) ;
 if not Result then CloseHandle(HFileRes) ;
 end; //IsFileInUse
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