SysUtils.FileOpen Function

Opens a specified file using a specified access mode.

Pascal

function FileOpen(const FileName: string; Mode: LongWord): Integer;

C++

int FileOpen(const AnsiString FileName, LongWord Mode);

File

SysUtils

Description

Use FileOpen to open a file and obtain a file handle. The access mode value is constructed by or-ing one of the fmOpen constants with one of the fmShare constants defined in File open mode constants. If the return value is 0 or greater, the function was successful and the value is the file handle of the opened file. A return value of -1 indicates that an error occurred.

Note: Use of the non-native Delphi language file handlers such as FileOpen is not encouraged. These routines map to system routines and return OS file handles, not normal Delphi file variables. These are low-level file access routines. For normal file operations use AssignFile, Rewrite, and Reset instead.

C++ Examples:

Copy Code

/*
The following example uses a button, a string grid, and an
Open dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the specified file is opened, read into a buffer, and closed.
Then the buffer is displayed in two columns of the string
grid. The first column contains the character values in the
buffer. The second column contains the numeric values of the
characters in the buffer.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  int iFileHandle;
  int iFileLength;
  int iBytesRead;
  char *pszBuffer;
  if (OpenDialog1->Execute())
  {
    try
    {
      iFileHandle = FileOpen(OpenDialog1->FileName, fmOpenRead);
      iFileLength = FileSeek(iFileHandle,0,2);
      FileSeek(iFileHandle,0,0);
      pszBuffer = new char[iFileLength+1];
      iBytesRead = FileRead(iFileHandle, pszBuffer, iFileLength);
      FileClose(iFileHandle);
      for (int i=0;i<iBytesRead;i++)
      {
        StringGrid1->RowCount += 1;
        StringGrid1->Cells[1][i+1] = pszBuffer[i];
        StringGrid1->Cells[2][i+1] = IntToStr((int)pszBuffer[i]);
      }
      delete [] pszBuffer;
    }
    catch(...)
    {
      Application->MessageBox("Can't perform one of the following file operations: Open, Seek, Read, Close.", "File Error", IDOK);
    }
  }
}

Delphi Examples:

Copy Code

{
This example uses a file listbox and a regular listbox on a
form. The following routine scans through the files listed
in the file listbox and lists the sizes of any selected
files to the regular list box.  To exercise the error
condition create a file in the Debug directory, start this
application and then delete the file.  Now try to list the
size of the deleted file.  Set the MultiSelect and
ExtendedSelect properties on the FileListBox.
}
procedure TForm1.Button1Click(Sender: TObject);
var
  F: File;
  i, filehandle: Integer;
begin
  for i := 0 to (FileListBox1.Items.Count - 1) do begin
  try
    if FileListBox1.Selected[i] then 
    begin
      if not FileExists(FileListBox1.Items.Strings[i]) then
      begin
        MessageDlg('File: ' + FileListBox1.Items.Strings[i] +
                   ' not found', mtError, [mbOk], 0);
        Continue;
      end;
      filehandle:=  FileOpen(FileListBox1.Items.Strings[i], 1);
      if (filehandle = -1) then
      begin
        MessageDlg('File: ' + FileListBox1.Items.Strings[i] +
                   ' cannot be opened with access mode 1.', mtError, [mbOk], 0);
        Continue;
      end
      else
        FileClose(filehandle);

      AssignFile(F, FileListBox1.Items.Strings[i]);
      Reset(F, 1);
      ListBox1.Items.Add(
        FileListBox1.Items.Strings[i] + ': ' + IntToStr(FileSize(F)));
      CloseFile(F);
    end;
   finally
   { do something here }
   end;
  end;
end;

Copy Code

{
This example requires a TEdit, a button and a string grid.
Enter the file name in the TEdit and click the button to open
that file.  Notice that the file cannot be read.  Remove the
fmOpenWrite and the fmShareDenyNone access and the string
grid loads fine.
}
procedure OpenForShare(const FileName: String);
var
  FileHandle : Integer;
  iFileLength: Integer;
  iBytesRead: Integer;
  Buffer: PChar;
  i: Integer;
begin
  FileHandle := SysUtils.FileOpen(FileName, fmOpenWrite or fmShareDenyNone or fmOpenRead);
  if FileHandle > 0 then
  begin
    try
      MessageDlg('Valid file handle.', mtInformation, [mbOk], 0);
      iFileLength := SysUtils.FileSeek(FileHandle,0,2);
      FileSeek(FileHandle, 0, 0);
      Buffer := PChar(System.AllocMem(iFileLength + 1));
      iBytesRead := SysUtils.FileRead(FileHandle, Buffer^, iFileLength);
      for i := 0 to iBytesRead-1 do
      begin
        Form1.StringGrid1.RowCount := Form1.StringGrid1.RowCount + 1;
        Form1.StringGrid1.Cells[1, i + 1] := Buffer[i];
        Form1.StringGrid1.Cells[2, i + 1] := IntToStr(Integer(Buffer[i]));
      end;
    finally
      FreeMem(Buffer);
    end;
  end
  else
    MessageDlg('Open error: FileHandle = negative DOS error code.', mtInformation, [mbOk], 0);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  OpenForShare(Edit1.Text);
end;

Copy Code

{
The following example uses a button, a string grid, and an
Open dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the specified file is opened, read into a buffer, and closed.
Then the buffer is displayed in two columns of the string
grid. The first column contains the character values in the
buffer. The second column contains the numeric values of the
characters in the buffer.
} 
procedure TForm1.Button1Click(Sender: TObject);
var
  iFileHandle: Integer;
  iFileLength: Integer;
  iBytesRead: Integer;
  Buffer: PChar;
  i: Integer;
begin
  if OpenDialog1.Execute then
  begin
    try
      iFileHandle := SysUtils.FileOpen(OpenDialog1.FileName, fmOpenRead);
      iFileLength := SysUtils.FileSeek(iFileHandle,0,2);
      FileSeek(iFileHandle,0,0);
      Buffer := PChar(System.AllocMem(iFileLength + 1));
      iBytesRead := SysUtils.FileRead(iFileHandle, Buffer^, iFileLength);
      FileClose(iFileHandle);
      for i := 0 to iBytesRead-1 do
      begin
        StringGrid1.RowCount := StringGrid1.RowCount + 1;
        StringGrid1.Cells[1,i+1] := Buffer[i];
        StringGrid1.Cells[2,i+1] := IntToStr(Integer(Buffer[i]));
      end;
    finally
      FreeMem(Buffer);
    end;
  end;
end;