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%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 case and character ranges.
%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
Incompatibilities with Lex and Posix. This option also results in the name
YY_FLEX_LEX_COMPAT being #define’d in the generated scanner.
%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.
%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
(see Performance Considerations). 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’
%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.
%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.
%option default’generate the default rule.
%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’instructs flex to generate a scanner which never considers its input
interactive. This is the opposite of always-interactive.
%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:
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.
%option stack’enables the use of start condition stacks (see Start Conditions).
%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.
%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.
%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).
Next: Code-Level And API Options, Previous: Options for Specifying Filenames, Up: Scanner Options [Contents][Index]