SetTextBuf

Declaration:

Procedure SetTextBuf (Var f : Text; Var Buf[; Size : Word]) ;

Description:

SetTextBuf assigns an I/O buffer to a text file. The new buffer is located at Buf and is Size bytes long. If Size is omitted, then SizeOf(Buf) is assumed.

The standard buffer of any text file is 128 bytes long. For heavy I/0 operations this may prove too slow. The SetTextBuf procedure allows you to set a bigger buffer for your application, thus reducing the number of system calls, and thus reducing the load on the system resources.

The maximum size of the newly assigned buffer is 65355 bytes.

Remark 1: Never assign a new buffer to an opened file. You can assign a new buffer immediately after a call to Rewrite, Reset or Append, but not after you read from/wrote to the file. This may cause loss of data. If you still want to assign a new buffer after read/write operations have been performed, flush the file first. This will ensure that the current buffer is emptied.

Remark 2: Take care that the buffer you assign is always valid. If you assign a local variable as a buffer, then after your program exits the local program block, the buffer will no longer be valid, and stack problems may occur.

Errors:

No checking on Size is done.

See also:

Assign, Reset, Rewrite, Append

Example

Program Example61;

{ Program to demonstrate the SetTextBuf function. }

Var
  Fin,Fout : Text;
  Ch : Char;
  Bufin,Bufout : Array[1..10000] of byte;
  
begin
  Assign (Fin,paramstr(1));
  Reset (Fin);
  Assign (Fout,paramstr(2));
  Rewrite (Fout);
  { This is harmless before IO has begun }
  { Try this program again on a big file,
    after commenting out the following 2 
    lines and recompiling it. }
  SetTextBuf (Fin,Bufin);
  SetTextBuf (Fout,Bufout);
  While not eof(Fin) do
    begin
    Read (Fin,ch);
    write (Fout,ch);
    end;
  Close (Fin);
  Close (Fout);
end.