[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

8.14.18 Trap runtime errors

The following listing contains the interface of the Trap unit.

This unit allows you to trap runtime errors, so a runtime error will not abort the program, but pass the control back to a point within the program. Use with care, and read the notes in the interface, please.

 
{ Trapping runtime errors

The Trap unit allows you to trap runtime errors, so a runtime error will not abort the program, but pass the control back to a point within the program.

The usage is simple. The TrapExec procedure can be called with a function (p) as an argument. p must take a Boolean argument. p will immediately be called with False given as its argument. When a runtime error would otherwise be caused while p is active, p will instead be called again with True as its argument. After p returns, runtime errors will not be trapped.

When the program terminates (e.g. by reaching its end or by a Halt statement) and a runtime error was trapped during the run, Trap will set the ExitCode and ErrorAddr variables to indicate the trapped error.

Notes:

- After trapping a runtime error, your program might not be in a stable state. If the runtime error was a "minor" one (such as a range checking or arithmetic error), it should not be a problem. But if you, e.g., write a larger application and use Trap to prevent a sudden abort caused by an unexpected runtime error, you should make the program terminate regularly as soon as possible after a trapped error (perhaps by telling the user to save the data, then terminate the program and report the bug to you).

- Since the trapping mechanism *jumps* back, it has all the negative effects that a (non-local!) `goto' can have! You should be aware of the consequences of all active procedures being terminated at an arbitrary point!

- Nested traps are supported, i.e. you can call TrapExec again within a routine called by another TrapExec instance. Runtime errors trapped within the inner TrapExec invocation will be trapped by the inner TrapExec, while runtime errors trapped after its termination will be trapped by the outer TrapExec again.

Copyright (C) 1996-2002 Free Software Foundation, Inc.

Author: Frank Heckenbach <frank@pascal.gnu.de>

This file is part of GNU Pascal.

GNU Pascal is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version.

GNU Pascal is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with GNU Pascal; see the file COPYING. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

As a special exception, if you link this file with files compiled with a GNU compiler to produce an executable, this does not cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. }

{$gnu-pascal,I-}

unit Trap;

interface

uses GPC;

var TrappedExitCode: Integer = 0; TrappedErrorAddr: Pointer = nil; TrappedErrorMessageString: TString = '';

{ Trap runtime errors. See the comment at the top. } procedure TrapExec (procedure p (Trapped: Boolean)); asmname '_p_trapexec';

{ Forget about saved errors from the innermost TrapExec instance. } procedure TrapReset; asmname '_p_trapreset';


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

This document was generated by Frank Heckenbach on May, 10 2002 using texi2html