(flex.info)Options Affecting Scanner Behavior

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16.2 Options Affecting Scanner Behavior
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'-i, --case-insensitive, '%option case-insensitive''
     instructs 'flex' to generate a "case-insensitive" scanner.  The
     case of letters given in the 'flex' input patterns will be ignored,
     and tokens in the input will be matched regardless of case.  The
     matched text given in 'yytext' will have the preserved case (i.e.,
     it will not be folded).  For tricky behavior, see Note: case and
     character ranges.

'-l, --lex-compat, '%option lex-compat''
     turns on maximum compatibility with the original AT&T 'lex'
     implementation.  Note that this does not mean _full_ compatibility.
     Use of this option costs a considerable amount of performance, and
     it cannot be used with the '--c++', '--full', '--fast', '-Cf', or
     '-CF' options.  For details on the compatibilities it provides, see
     Note: Lex and Posix.  This option also results in the name
     'YY_FLEX_LEX_COMPAT' being '#define''d in the generated scanner.

'-B, --batch, '%option batch''
     instructs 'flex' to generate a "batch" scanner, the opposite of
     _interactive_ scanners generated by '--interactive' (see below).
     In general, you use '-B' when you are _certain_ that your scanner
     will never be used interactively, and you want to squeeze a
     _little_ more performance out of it.  If your goal is instead to
     squeeze out a _lot_ more performance, you should be using the '-Cf'
     or '-CF' options, which turn on '--batch' automatically anyway.

'-I, --interactive, '%option interactive''
     instructs 'flex' to generate an interactive scanner.  An
     interactive scanner is one that only looks ahead to decide what
     token has been matched if it absolutely must.  It turns out that
     always looking one extra character ahead, even if the scanner has
     already seen enough text to disambiguate the current token, is a
     bit faster than only looking ahead when necessary.  But scanners
     that always look ahead give dreadful interactive performance; for
     example, when a user types a newline, it is not recognized as a
     newline token until they enter _another_ token, which often means
     typing in another whole line.

     'flex' scanners default to 'interactive' unless you use the '-Cf'
     or '-CF' table-compression options (Note: Performance).  That's
     because if you're looking for high-performance you should be using
     one of these options, so if you didn't, 'flex' assumes you'd rather
     trade off a bit of run-time performance for intuitive interactive
     behavior.  Note also that you _cannot_ use '--interactive' in
     conjunction with '-Cf' or '-CF'.  Thus, this option is not really
     needed; it is on by default for all those cases in which it is
     allowed.

     You can force a scanner to _not_ be interactive by using '--batch'

'-7, --7bit, '%option 7bit''
     instructs 'flex' to generate a 7-bit scanner, i.e., one which can
     only recognize 7-bit characters in its input.  The advantage of
     using '--7bit' is that the scanner's tables can be up to half the
     size of those generated using the '--8bit'.  The disadvantage is
     that such scanners often hang or crash if their input contains an
     8-bit character.

     Note, however, that unless you generate your scanner using the
     '-Cf' or '-CF' table compression options, use of '--7bit' will save
     only a small amount of table space, and make your scanner
     considerably less portable.  'Flex''s default behavior is to
     generate an 8-bit scanner unless you use the '-Cf' or '-CF', in
     which case 'flex' defaults to generating 7-bit scanners unless your
     site was always configured to generate 8-bit scanners (as will
     often be the case with non-USA sites).  You can tell whether flex
     generated a 7-bit or an 8-bit scanner by inspecting the flag
     summary in the '--verbose' output as described above.

     Note that if you use '-Cfe' or '-CFe' 'flex' still defaults to
     generating an 8-bit scanner, since usually with these compression
     options full 8-bit tables are not much more expensive than 7-bit
     tables.

'-8, --8bit, '%option 8bit''
     instructs 'flex' to generate an 8-bit scanner, i.e., one which can
     recognize 8-bit characters.  This flag is only needed for scanners
     generated using '-Cf' or '-CF', as otherwise flex defaults to
     generating an 8-bit scanner anyway.

     See the discussion of '--7bit' above for 'flex''s default behavior
     and the tradeoffs between 7-bit and 8-bit scanners.

'--default, '%option default''
     generate the default rule.

'--always-interactive, '%option always-interactive''
     instructs flex to generate a scanner which always considers its
     input _interactive_.  Normally, on each new input file the scanner
     calls 'isatty()' in an attempt to determine whether the scanner's
     input source is interactive and thus should be read a character at
     a time.  When this option is used, however, then no such call is
     made.

'--never-interactive, '--never-interactive''
     instructs flex to generate a scanner which never considers its
     input interactive.  This is the opposite of 'always-interactive'.

'-X, --posix, '%option posix''
     turns on maximum compatibility with the POSIX 1003.2-1992
     definition of 'lex'.  Since 'flex' was originally designed to
     implement the POSIX definition of 'lex' this generally involves
     very few changes in behavior.  At the current writing the known
     differences between 'flex' and the POSIX standard are:

        * In POSIX and AT&T 'lex', the repeat operator, '{}', has lower
          precedence than concatenation (thus 'ab{3}' yields 'ababab').
          Most POSIX utilities use an Extended Regular Expression (ERE)
          precedence that has the precedence of the repeat operator
          higher than concatenation (which causes 'ab{3}' to yield
          'abbb').  By default, 'flex' places the precedence of the
          repeat operator higher than concatenation which matches the
          ERE processing of other POSIX utilities.  When either
          '--posix' or '-l' are specified, 'flex' will use the
          traditional AT&T and POSIX-compliant precedence for the repeat
          operator where concatenation has higher precedence than the
          repeat operator.

'--stack, '%option stack''
     enables the use of start condition stacks (Note: Start
     Conditions).

'--stdinit, '%option stdinit''
     if set (i.e., %option stdinit) initializes 'yyin' and 'yyout' to
     'stdin' and 'stdout', instead of the default of 'NULL'.  Some
     existing 'lex' programs depend on this behavior, even though it is
     not compliant with ANSI C, which does not require 'stdin' and
     'stdout' to be compile-time constant.  In a reentrant scanner,
     however, this is not a problem since initialization is performed in
     'yylex_init' at runtime.

'--yylineno, '%option yylineno''
     directs 'flex' to generate a scanner that maintains the number of
     the current line read from its input in the global variable
     'yylineno'.  This option is implied by '%option lex-compat'.  In a
     reentrant C scanner, the macro 'yylineno' is accessible regardless
     of the value of '%option yylineno', however, its value is not
     modified by 'flex' unless '%option yylineno' is enabled.

'--yywrap, '%option yywrap''
     if unset (i.e., '--noyywrap)', makes the scanner not call
     'yywrap()' upon an end-of-file, but simply assume that there are no
     more files to scan (until the user points 'yyin' at a new file and
     calls 'yylex()' again).