From bug-octave-request at bevo dot che dot wisc dot edu  Fri Nov 14 02:05:56 1997
Subject: Interpretation of '\' in strings
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Maximilian Pitschi <Maximilian dot Pitschi at ofw dot pr dot siemens dot de>
Cc: bug-octave at bevo dot che dot wisc dot edu
Date: Fri, 14 Nov 1997 02:03:04 -0600

On 23-Sep-1997, Maximilian Pitschi <Maximilian dot Pitschi at ofw dot pr dot siemens dot de> wrote:

| Bug report for Octave 2.0.9 configured for hppa1.1-hp-hpux10.20
| 
| Description:
| -----------
| 
| Octave with --traditional interprets '\' as an escape character.
| In matlab, in normal strings, i.e., no format strings, '\' has no
| special meaning.
| 
| Repeat-By:
| ---------
| 
| Octave, version 2.0.9 (hppa1.1-hp-hpux10.20).
| Copyright (C) 1996, 1997 John W. Eaton.
| This is free software with ABSOLUTELY NO WARRANTY.
| For details, type `warranty'.
| 
| octave:1> '\[' 
| warning: unrecognized escape sequence `\[' -- converting to `['
| ans = [
| 
| or even worse:
| 
| octave:1> '\'
| error: unterminated string constant
| parse error:
| 
| >>> '\'
| 			 ^
| 
| The examples should return '\[' and '\', respectively.

Here is a patch to try.  It should turn off all special interpretation
of backslash characters in strings, as well as turning off their use
as a continuation line marker if you set the new variable
`backslash_escapes' to 0.  The default value is 1 unless you use the
--traditional or --brain-dead options.  Unless someone points out a
major flaw with this, it should be in 2.0.10.

Thanks,

jwe


Fri Nov 14 01:53:13 1997  John W. Eaton  <jwe at bevo dot che dot wisc dot edu>

	* lex.l (Vbackslash_escapes): New static variable.
	(backslash_escapes): New function.
	(do_string_escapes): Return immediately if ! Vbackslash_escapes.
	(eat_whitespace, eat_continuation): Only call have_continuation if
	Vbackslash_escapes.
	(handle_string): Backslash is only special if Vbackslash_escapes.
	(symbols_of_lex): Add DEFVAR for backslash_escapes.
	* octave.cc (maximum_braindamage): Set backslash_escapes to 0.


*** src/lex.l~	Mon May 19 20:10:10 1997
--- src/lex.l	Fri Nov 14 01:46:42 1997
***************
*** 162,167 ****
--- 162,170 ----
  
  static int Vwhitespace_in_literal_matrix;
  
+ // Should Octave treat backslashes in strings as escapes that
+ // introduce special characters like newline (\n), tab (\t), etc.?
+ static bool Vbackslash_escapes;
  
  // Forward declarations for functions defined at the bottom of this
  // file.
***************
*** 705,710 ****
--- 708,716 ----
  static void
  do_string_escapes (char *s)
  {
+   if (! Vbackslash_escapes)
+     return;
+ 
    char *p1 = s;
    char *p2 = s;
    while (*p2 != '\0')
***************
*** 1344,1350 ****
  	    break;
  	  else
  	    {
! 	      if (have_continuation ())
  		break;
  	      else
  		goto done;
--- 1350,1356 ----
  	    break;
  	  else
  	    {
! 	      if (Vbackslash_escapes && have_continuation ())
  		break;
  	      else
  		goto done;
***************
*** 1498,1504 ****
    int retval = ATE_NOTHING;
    int c = yyinput ();
    if ((c == '.' && have_ellipsis_continuation ())
!       || (c == '\\' && have_continuation ()))
      retval = eat_whitespace ();
    else
      yyunput (c, yytext);
--- 1504,1510 ----
    int retval = ATE_NOTHING;
    int c = yyinput ();
    if ((c == '.' && have_ellipsis_continuation ())
!       || (c == '\\' && Vbackslash_escapes && have_continuation ()))
      retval = eat_whitespace ();
    else
      yyunput (c, yytext);
***************
*** 1518,1524 ****
      {
        current_input_column++;
  
!       if (c == '\\')
  	{
  	  if (escape_pending)
  	    {
--- 1524,1530 ----
      {
        current_input_column++;
  
!       if (c == '\\' && Vbackslash_escapes)
  	{
  	  if (escape_pending)
  	    {
***************
*** 1937,1942 ****
--- 1943,1956 ----
  }
  
  int
+ backslash_escapes (void)
+ {
+   Vbackslash_escapes = check_preference ("backslash_escapes");
+ 
+   return 0;
+ }
+ 
+ int
  whitespace_in_literal_matrix (void)
  {
    int pref = 0;
***************
*** 1955,1960 ****
--- 1969,1978 ----
  void
  symbols_of_lex (void)
  {
+   DEFVAR (backslash_escapes, 1.0, 0, backslash_escapes,
+     "if nonzero, Octave recognizes backslashes in strings as escapes that\n\
+ introduce special characters like newline (\\n), tab (\\t), etc.");
+ 
    DEFVAR (whitespace_in_literal_matrix, "", 0, whitespace_in_literal_matrix,
      "control auto-insertion of commas and semicolons in literal matrices");
  }
*** src/octave.cc~	Mon May 19 20:33:05 1997
--- src/octave.cc	Fri Nov 14 01:44:09 1997
***************
*** 374,379 ****
--- 374,380 ----
  {
    bind_builtin_variable ("PS1", ">> ");
    bind_builtin_variable ("PS2", "");
+   bind_builtin_variable ("backslash_escapes", 0.0);
    bind_builtin_variable ("beep_on_error", 1.0);
    bind_builtin_variable ("default_eval_print_flag", 0.0);
    bind_builtin_variable ("default_save_format", "mat-binary");