SysUtils.FileSeek Function

Repositions read/write point.

Pascal

function FileSeek(Handle: Integer; Offset: Integer; Origin: Integer): Integer; overload;
function FileSeek(Handle: Integer; const Offset: Int64; Origin: Integer): Int64; overload;

C++

int FileSeek(int Handle, int Offset, int Origin);
Int64 FileSeek(int Handle, const Int64 Offset, int Origin);

File

SysUtils

Description

Use FileSeek to reposition the read/write point in a file that was opened with FileOpen or FileCreate. Handle is the file handle that was returned by FileOpen or FileCreate.

Offset specifies the number of bytes from Origin where the file pointer should be positioned. Origin is a code with three possible values, denoting the beginning of the file, the end of the file, and the current position of the file pointer.

Origin	Action
0	The file pointer is positioned Offset bytes from the beginning of the file.
1	The file pointer is positioned Offset bytes from its current position.
2	The file pointer is positioned Offset bytes from the end of the file.

If FileSeek is successful, it returns the new position of the file pointer; otherwise, it returns -1.

Note: :Do not mix routines that take or return file handles with those that use Delphi language file variables (typically seen as var F). To move the file pointer in a file specified by a Delphi file variable, use the Seek procedure 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 = PChar(AllocMem(iFileLength+1));
//    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

{
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;