[Overview][Constants][Types][Procedures and functions][Index] Reference for unit 'BaseUnix' (#rtl)


Duplicate a file handle


Source position: bunxh.inc line 38

function FpDup(

  fildes: cint


function FpDup(

  var oldfile: text;

  var newfile: text


function FpDup(

  var oldfile: file;

  var newfile: file



FpDup returns a file descriptor that is a duplicate of the file descriptor fildes.

The second and third forms make NewFile an exact copy of OldFile, after having flushed the buffer of OldFile in case it is a Text file or untyped file. Due to the buffering mechanism of Pascal, these calls do not have the same functionality as the dup call in C. The internal Pascal buffers are not the same after this call, but when the buffers are flushed (e.g. after output), the output is sent to the same file. Doing an lseek will, however, work as in C, i.e. doing a lseek will change the fileposition in both files.

The function returns a negative value in case of an error, a positive value is a file handle, and indicates succes.


A negative value can be one of the following error codes:

OldFile hasn't been assigned.
Maximum number of open files for the process is reached.

See also



Duplicate one filehandle to another


program Example31;

{ Program to demonstrate the Dup function. }

uses baseunix;

var f : text;

  if  fpdup (output,f)=-1 then
    Writeln ('Dup Failed !');
  writeln ('This is written to stdout.');
  writeln (f,'This is written to the dup file, and flushed');flush(f);

Documentation generated on: Mar 17 2017