SysUtils.FileRead Function

Reads a specified number of bytes from a file.

Pascal

function FileRead(Handle: Integer; var Buffer; Count: LongWord): Integer;

C++

int FileRead(int Handle,  Buffer, LongWord Count);

File

SysUtils

Description

FileRead reads Count bytes from the file specified by Handle into the buffer. The Count parameter indicates the size, in bytes, of the buffer. The function result is the actual number of bytes read, which may be less than Count. The Handle that is passed to FileRead must be opened with FileOpen or FileCreate.

Note: :In Delphi, do not mix routines that take or return file handles with those that use Delphi language file variables (typically seen as var F). To read from a file specified by a Delphi file variable, use the BlockRead procedure or the Read 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;