From bug-octave-request at che dot utexas dot edu  Wed Aug 17 09:55:15 1994
Subject: Octave "break" bug ?
From: "R.D. Auchterlounie" <rda at eng dot cam dot ac dot uk>
To: bug-octave at che dot utexas dot edu
Date: Wed, 17 Aug 1994 15:55:04 BST

1;    % -*- Octave script file -*-
%
% Octave bug report.
% ------------------
%
% Summary: "break" sometimes breaks out of more than one level of 
%          nested for loops.
%
% Reproducing the bug:    Save this message to a script file and execute it. 
% 	 
% Info:    Octave version:  1.0
%          Machine:         AMD486DX40 PC
%          OS:              Linux v1.0
%	   Configuration:   Binary distribution - with no modifications 
%                             to octave source according to accompanying
%                             information file.
%          From:            rda at eng dot cam dot ac dot uk
%
% Detail:  
% 
% This problem occurred in a program of mine which has several nested
% for loops.  The limits on the loop range for the inner loop are
% variable, in some cases the inner loop may only be a single
% iteration. If a certain condition occurred I wished to terminate the
% innermost loop - which should be achievable with a "break"
% statement. Unfortunately using "break" lead to errors which I have
% traced to the break statement breaking out of TWO levels of loop.
%
% The following function is a simple demonstration of the bug, it
% contains 3 levels of "for" loops. The outer loop is two iterations,
% the middle loop is 3 (1:3). The inner loop should terminate after 1
% iteration (only) when the middle loop variable is 2. The range
% limits for the inner loop are passed as the two function arguments.
%
% The use of fprintf "'" and "end" allow the function to be run unchanged
% by Matlab4. 
%
function loop(a,b);
  fprintf(1,'\n*** loop called with %d,%d\n',a,b)
  for l=1:2
    fprintf(1,'---------------------------- outer loop %d\n',l)
    for m=1:3
      fprintf(1,'------------- middle loop %d\n',m)
      for n=a:b
	fprintf(1,'inner loop %d\n',n);
	if (m==2)
	  % as far as I can see this should terminate (only) the inner
	  % for loop after the first iteration, on the second iteration
	  % of the outer loop.
	  fprintf(1,'break inner\n');
	  break; 
	end ; % if
      end ; % inner for
    end ; % middle for
  end ; % outer for
end ; % function
%
%
% When the function is called with unequal arguments, eg:
%
loop(1,2)
%
% we get the expected results - twice round the outer loop, three
% times round the middle loop and a variable number of times round the
% inner loop. This also works for zero inner loop iterations, eg:
%
loop(2,1)
%
% But when I want one inner loop iteration, eg:
%
loop(1,1)
%
% The _middle_ loop is broken after the break is executed in the inner
% loop. When the same function is tested in Matlab the middle loop is
% not broken.
%
% Thanks for any help.
% ray