1002 lines
25 KiB
Groff
1002 lines
25 KiB
Groff
.TH FLEX 1 "November 1993" "Version 2.4"
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.SH NAME
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flex \- fast lexical analyzer generator
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.SH SYNOPSIS
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.B flex
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.B [\-bcdfhilnpstvwBFILTV78+ \-C[aefFmr] \-Pprefix \-Sskeleton]
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.I [filename ...]
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.SH DESCRIPTION
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.I flex
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is a tool for generating
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.I scanners:
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programs which recognized lexical patterns in text.
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.I flex
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reads
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the given input files, or its standard input if no file names are given,
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for a description of a scanner to generate. The description is in
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the form of pairs
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of regular expressions and C code, called
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.I rules. flex
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generates as output a C source file,
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.B lex.yy.c,
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which defines a routine
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.B yylex().
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This file is compiled and linked with the
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.B \-lfl
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library to produce an executable. When the executable is run,
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it analyzes its input for occurrences
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of the regular expressions. Whenever it finds one, it executes
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the corresponding C code.
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.PP
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For full documentation, see
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.B flexdoc(1).
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This manual entry is intended for use as a quick reference.
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.SH OPTIONS
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.I flex
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has the following options:
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.TP
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.B \-b
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generate backing-up information to
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.I lex.backup.
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This is a list of scanner states which require backing up and the input
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characters on which they do so. By adding rules one can remove
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backing-up states. If all backing-up states are eliminated and
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.B \-Cf
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or
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.B \-CF
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is used, the generated scanner will run faster.
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.TP
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.B \-c
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is a do-nothing, deprecated option included for POSIX compliance.
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.IP
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.B NOTE:
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in previous releases of
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.I flex
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.B \-c
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specified table-compression options. This functionality is
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now given by the
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.B \-C
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flag. To ease the the impact of this change, when
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.I flex
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encounters
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.B \-c,
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it currently issues a warning message and assumes that
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.B \-C
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was desired instead. In the future this "promotion" of
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.B \-c
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to
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.B \-C
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will go away in the name of full POSIX compliance (unless
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the POSIX meaning is removed first).
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.TP
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.B \-d
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makes the generated scanner run in
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.I debug
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mode. Whenever a pattern is recognized and the global
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.B yy_flex_debug
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is non-zero (which is the default), the scanner will
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write to
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.I stderr
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a line of the form:
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.nf
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--accepting rule at line 53 ("the matched text")
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.fi
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The line number refers to the location of the rule in the file
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defining the scanner (i.e., the file that was fed to flex). Messages
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are also generated when the scanner backs up, accepts the
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default rule, reaches the end of its input buffer (or encounters
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a NUL; the two look the same as far as the scanner's concerned),
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or reaches an end-of-file.
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.TP
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.B \-f
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specifies
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.I fast scanner.
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No table compression is done and stdio is bypassed.
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The result is large but fast. This option is equivalent to
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.B \-Cfr
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(see below).
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.TP
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.B \-h
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generates a "help" summary of
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.I flex's
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options to
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.I stderr
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and then exits.
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.TP
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.B \-i
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instructs
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.I flex
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to generate a
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.I case-insensitive
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scanner. The case of letters given in the
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.I flex
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input patterns will
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be ignored, and tokens in the input will be matched regardless of case. The
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matched text given in
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.I yytext
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will have the preserved case (i.e., it will not be folded).
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.TP
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.B \-l
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turns on maximum compatibility with the original AT&T lex implementation,
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at a considerable performance cost. This option is incompatible with
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.B \-+, \-f, \-F, \-Cf,
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or
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.B \-CF.
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See
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.I flexdoc(1)
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for details.
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.TP
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.B \-n
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is another do-nothing, deprecated option included only for
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POSIX compliance.
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.TP
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.B \-p
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generates a performance report to stderr. The report
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consists of comments regarding features of the
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.I flex
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input file which will cause a loss of performance in the resulting scanner.
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If you give the flag twice, you will also get comments regarding
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features that lead to minor performance losses.
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.TP
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.B \-s
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causes the
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.I default rule
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(that unmatched scanner input is echoed to
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.I stdout)
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to be suppressed. If the scanner encounters input that does not
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match any of its rules, it aborts with an error.
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.TP
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.B \-t
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instructs
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.I flex
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to write the scanner it generates to standard output instead
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of
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.B lex.yy.c.
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.TP
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.B \-v
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specifies that
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.I flex
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should write to
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.I stderr
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a summary of statistics regarding the scanner it generates.
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.TP
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.B \-w
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suppresses warning messages.
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.TP
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.B \-B
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instructs
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.I flex
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to generate a
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.I batch
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scanner instead of an
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.I interactive
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scanner (see
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.B \-I
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below). See
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.I flexdoc(1)
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for details. Scanners using
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.B \-Cf
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or
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.B \-CF
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compression options automatically specify this option, too.
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.TP
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.B \-F
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specifies that the
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.ul
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fast
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scanner table representation should be used (and stdio bypassed).
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This representation is about as fast as the full table representation
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.B (-f),
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and for some sets of patterns will be considerably smaller (and for
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others, larger). It cannot be used with the
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.B \-+
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option. See
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.B flexdoc(1)
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for more details.
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.IP
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This option is equivalent to
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.B \-CFr
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(see below).
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.TP
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.B \-I
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instructs
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.I flex
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to generate an
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.I interactive
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scanner, that is, a scanner which stops immediately rather than
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looking ahead if it knows
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that the currently scanned text cannot be part of a longer rule's match.
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This is the opposite of
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.I batch
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scanners (see
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.B \-B
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above). See
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.B flexdoc(1)
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for details.
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.IP
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Note,
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.B \-I
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cannot be used in conjunction with
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.I full
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or
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.I fast tables,
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i.e., the
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.B \-f, \-F, \-Cf,
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or
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.B \-CF
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flags. For other table compression options,
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.B \-I
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is the default.
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.TP
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.B \-L
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instructs
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.I flex
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not to generate
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.B #line
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directives in
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.B lex.yy.c.
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The default is to generate such directives so error
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messages in the actions will be correctly
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located with respect to the original
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.I flex
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input file, and not to
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the fairly meaningless line numbers of
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.B lex.yy.c.
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.TP
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.B \-T
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makes
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.I flex
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run in
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.I trace
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mode. It will generate a lot of messages to
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.I stderr
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concerning
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the form of the input and the resultant non-deterministic and deterministic
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finite automata. This option is mostly for use in maintaining
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.I flex.
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.TP
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.B \-V
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prints the version number to
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.I stderr
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and exits.
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.TP
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.B \-7
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instructs
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.I flex
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to generate a 7-bit scanner, which can save considerable table space,
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especially when using
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.B \-Cf
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or
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.B \-CF
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(and, at most sites,
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.B \-7
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is on by default for these options. To see if this is the case, use the
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.B -v
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verbose flag and check the flag summary it reports).
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.TP
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.B \-8
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instructs
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.I flex
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to generate an 8-bit scanner. This is the default except for the
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.B \-Cf
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and
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.B \-CF
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compression options, for which the default is site-dependent, and
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can be checked by inspecting the flag summary generated by the
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.B \-v
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option.
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.TP
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.B \-+
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specifies that you want flex to generate a C++
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scanner class. See the section on Generating C++ Scanners in
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.I flexdoc(1)
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for details.
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.TP
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.B \-C[aefFmr]
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controls the degree of table compression and scanner optimization.
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.IP
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.B \-Ca
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trade off larger tables in the generated scanner for faster performance
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because the elements of the tables are better aligned for memory access
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and computation. This option can double the size of the tables used by
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your scanner.
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.IP
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.B \-Ce
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directs
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.I flex
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to construct
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.I equivalence classes,
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i.e., sets of characters
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which have identical lexical properties.
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Equivalence classes usually give
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dramatic reductions in the final table/object file sizes (typically
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a factor of 2-5) and are pretty cheap performance-wise (one array
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look-up per character scanned).
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.IP
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.B \-Cf
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specifies that the
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.I full
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scanner tables should be generated -
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.I flex
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should not compress the
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tables by taking advantages of similar transition functions for
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different states.
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.IP
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.B \-CF
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specifies that the alternate fast scanner representation (described in
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.B flexdoc(1))
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should be used. This option cannot be used with
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.B \-+.
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.IP
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.B \-Cm
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directs
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.I flex
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to construct
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.I meta-equivalence classes,
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which are sets of equivalence classes (or characters, if equivalence
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classes are not being used) that are commonly used together. Meta-equivalence
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classes are often a big win when using compressed tables, but they
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have a moderate performance impact (one or two "if" tests and one
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array look-up per character scanned).
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.IP
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.B \-Cr
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causes the generated scanner to
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.I bypass
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using stdio for input. In general this option results in a minor
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performance gain only worthwhile if used in conjunction with
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.B \-Cf
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or
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.B \-CF.
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It can cause surprising behavior if you use stdio yourself to
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read from
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.I yyin
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prior to calling the scanner.
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.IP
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A lone
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.B \-C
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specifies that the scanner tables should be compressed but neither
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equivalence classes nor meta-equivalence classes should be used.
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.IP
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The options
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.B \-Cf
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or
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.B \-CF
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and
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.B \-Cm
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do not make sense together - there is no opportunity for meta-equivalence
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classes if the table is not being compressed. Otherwise the options
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may be freely mixed.
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.IP
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The default setting is
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.B \-Cem,
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which specifies that
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.I flex
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should generate equivalence classes
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and meta-equivalence classes. This setting provides the highest
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degree of table compression. You can trade off
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faster-executing scanners at the cost of larger tables with
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the following generally being true:
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.nf
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slowest & smallest
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-Cem
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-Cm
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-Ce
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-C
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-C{f,F}e
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-C{f,F}
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-C{f,F}a
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fastest & largest
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.fi
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.IP
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.B \-C
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options are cumulative.
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.TP
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.B \-Pprefix
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changes the default
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.I "yy"
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prefix used by
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.I flex
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to be
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.I prefix
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instead. See
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.I flexdoc(1)
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for a description of all the global variables and file names that
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this affects.
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.TP
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.B \-Sskeleton_file
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overrides the default skeleton file from which
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.I flex
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constructs its scanners. You'll never need this option unless you are doing
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.I flex
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maintenance or development.
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.SH SUMMARY OF FLEX REGULAR EXPRESSIONS
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The patterns in the input are written using an extended set of regular
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expressions. These are:
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.nf
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x match the character 'x'
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. any character except newline
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[xyz] a "character class"; in this case, the pattern
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matches either an 'x', a 'y', or a 'z'
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[abj-oZ] a "character class" with a range in it; matches
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an 'a', a 'b', any letter from 'j' through 'o',
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or a 'Z'
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[^A-Z] a "negated character class", i.e., any character
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but those in the class. In this case, any
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character EXCEPT an uppercase letter.
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[^A-Z\\n] any character EXCEPT an uppercase letter or
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a newline
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r* zero or more r's, where r is any regular expression
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r+ one or more r's
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r? zero or one r's (that is, "an optional r")
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r{2,5} anywhere from two to five r's
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r{2,} two or more r's
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r{4} exactly 4 r's
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{name} the expansion of the "name" definition
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(see above)
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"[xyz]\\"foo"
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the literal string: [xyz]"foo
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\\X if X is an 'a', 'b', 'f', 'n', 'r', 't', or 'v',
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then the ANSI-C interpretation of \\x.
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Otherwise, a literal 'X' (used to escape
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operators such as '*')
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\\123 the character with octal value 123
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\\x2a the character with hexadecimal value 2a
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(r) match an r; parentheses are used to override
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precedence (see below)
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rs the regular expression r followed by the
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regular expression s; called "concatenation"
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r|s either an r or an s
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r/s an r but only if it is followed by an s. The
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s is not part of the matched text. This type
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of pattern is called as "trailing context".
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^r an r, but only at the beginning of a line
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r$ an r, but only at the end of a line. Equivalent
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to "r/\\n".
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<s>r an r, but only in start condition s (see
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below for discussion of start conditions)
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<s1,s2,s3>r
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same, but in any of start conditions s1,
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s2, or s3
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<*>r an r in any start condition, even an exclusive one.
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<<EOF>> an end-of-file
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<s1,s2><<EOF>>
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an end-of-file when in start condition s1 or s2
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.fi
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The regular expressions listed above are grouped according to
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precedence, from highest precedence at the top to lowest at the bottom.
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Those grouped together have equal precedence.
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.PP
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Some notes on patterns:
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.IP -
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Negated character classes
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.I match newlines
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unless "\\n" (or an equivalent escape sequence) is one of the
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characters explicitly present in the negated character class
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(e.g., "[^A-Z\\n]").
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.IP -
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A rule can have at most one instance of trailing context (the '/' operator
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or the '$' operator). The start condition, '^', and "<<EOF>>" patterns
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can only occur at the beginning of a pattern, and, as well as with '/' and '$',
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cannot be grouped inside parentheses. The following are all illegal:
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.nf
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foo/bar$
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foo|(bar$)
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foo|^bar
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<sc1>foo<sc2>bar
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.fi
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.SH SUMMARY OF SPECIAL ACTIONS
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In addition to arbitrary C code, the following can appear in actions:
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.IP -
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.B ECHO
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copies yytext to the scanner's output.
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.IP -
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.B BEGIN
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followed by the name of a start condition places the scanner in the
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corresponding start condition.
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.IP -
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.B REJECT
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directs the scanner to proceed on to the "second best" rule which matched the
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input (or a prefix of the input).
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.B yytext
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and
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.B yyleng
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are set up appropriately. Note that
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.B REJECT
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is a particularly expensive feature in terms scanner performance;
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if it is used in
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.I any
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of the scanner's actions it will slow down
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.I all
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of the scanner's matching. Furthermore,
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.B REJECT
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cannot be used with the
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.B \-f
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or
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.B \-F
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options.
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.IP
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Note also that unlike the other special actions,
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.B REJECT
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is a
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.I branch;
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code immediately following it in the action will
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.I not
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be executed.
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.IP -
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.B yymore()
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tells the scanner that the next time it matches a rule, the corresponding
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token should be
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.I appended
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onto the current value of
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.B yytext
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rather than replacing it.
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.IP -
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.B yyless(n)
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returns all but the first
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.I n
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characters of the current token back to the input stream, where they
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will be rescanned when the scanner looks for the next match.
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.B yytext
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and
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.B yyleng
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are adjusted appropriately (e.g.,
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.B yyleng
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will now be equal to
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.I n
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).
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.IP -
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.B unput(c)
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puts the character
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.I c
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back onto the input stream. It will be the next character scanned.
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.IP -
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.B input()
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reads the next character from the input stream (this routine is called
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.B yyinput()
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if the scanner is compiled using
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.B C++).
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.IP -
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.B yyterminate()
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can be used in lieu of a return statement in an action. It terminates
|
|
the scanner and returns a 0 to the scanner's caller, indicating "all done".
|
|
.IP
|
|
By default,
|
|
.B yyterminate()
|
|
is also called when an end-of-file is encountered. It is a macro and
|
|
may be redefined.
|
|
.IP -
|
|
.B YY_NEW_FILE
|
|
is an action available only in <<EOF>> rules. It means "Okay, I've
|
|
set up a new input file, continue scanning". It is no longer required;
|
|
you can just assign
|
|
.I yyin
|
|
to point to a new file in the <<EOF>> action.
|
|
.IP -
|
|
.B yy_create_buffer( file, size )
|
|
takes a
|
|
.I FILE
|
|
pointer and an integer
|
|
.I size.
|
|
It returns a YY_BUFFER_STATE
|
|
handle to a new input buffer large enough to accomodate
|
|
.I size
|
|
characters and associated with the given file. When in doubt, use
|
|
.B YY_BUF_SIZE
|
|
for the size.
|
|
.IP -
|
|
.B yy_switch_to_buffer( new_buffer )
|
|
switches the scanner's processing to scan for tokens from
|
|
the given buffer, which must be a YY_BUFFER_STATE.
|
|
.IP -
|
|
.B yy_delete_buffer( buffer )
|
|
deletes the given buffer.
|
|
.SH VALUES AVAILABLE TO THE USER
|
|
.IP -
|
|
.B char *yytext
|
|
holds the text of the current token. It may be modified but not lengthened
|
|
(you cannot append characters to the end). Modifying the last character
|
|
may affect the activity of rules anchored using '^' during the next scan;
|
|
see
|
|
.B flexdoc(1)
|
|
for details.
|
|
.IP
|
|
If the special directive
|
|
.B %array
|
|
appears in the first section of the scanner description, then
|
|
.B yytext
|
|
is instead declared
|
|
.B char yytext[YYLMAX],
|
|
where
|
|
.B YYLMAX
|
|
is a macro definition that you can redefine in the first section
|
|
if you don't like the default value (generally 8KB). Using
|
|
.B %array
|
|
results in somewhat slower scanners, but the value of
|
|
.B yytext
|
|
becomes immune to calls to
|
|
.I input()
|
|
and
|
|
.I unput(),
|
|
which potentially destroy its value when
|
|
.B yytext
|
|
is a character pointer. The opposite of
|
|
.B %array
|
|
is
|
|
.B %pointer,
|
|
which is the default.
|
|
.IP
|
|
You cannot use
|
|
.B %array
|
|
when generating C++ scanner classes
|
|
(the
|
|
.B \-+
|
|
flag).
|
|
.IP -
|
|
.B int yyleng
|
|
holds the length of the current token.
|
|
.IP -
|
|
.B FILE *yyin
|
|
is the file which by default
|
|
.I flex
|
|
reads from. It may be redefined but doing so only makes sense before
|
|
scanning begins or after an EOF has been encountered. Changing it in
|
|
the midst of scanning will have unexpected results since
|
|
.I flex
|
|
buffers its input; use
|
|
.B yyrestart()
|
|
instead.
|
|
Once scanning terminates because an end-of-file
|
|
has been seen,
|
|
.B
|
|
you can assign
|
|
.I yyin
|
|
at the new input file and then call the scanner again to continue scanning.
|
|
.IP -
|
|
.B void yyrestart( FILE *new_file )
|
|
may be called to point
|
|
.I yyin
|
|
at the new input file. The switch-over to the new file is immediate
|
|
(any previously buffered-up input is lost). Note that calling
|
|
.B yyrestart()
|
|
with
|
|
.I yyin
|
|
as an argument thus throws away the current input buffer and continues
|
|
scanning the same input file.
|
|
.IP -
|
|
.B FILE *yyout
|
|
is the file to which
|
|
.B ECHO
|
|
actions are done. It can be reassigned by the user.
|
|
.IP -
|
|
.B YY_CURRENT_BUFFER
|
|
returns a
|
|
.B YY_BUFFER_STATE
|
|
handle to the current buffer.
|
|
.IP -
|
|
.B YY_START
|
|
returns an integer value corresponding to the current start
|
|
condition. You can subsequently use this value with
|
|
.B BEGIN
|
|
to return to that start condition.
|
|
.SH MACROS AND FUNCTIONS YOU CAN REDEFINE
|
|
.IP -
|
|
.B YY_DECL
|
|
controls how the scanning routine is declared.
|
|
By default, it is "int yylex()", or, if prototypes are being
|
|
used, "int yylex(void)". This definition may be changed by redefining
|
|
the "YY_DECL" macro. Note that
|
|
if you give arguments to the scanning routine using a
|
|
K&R-style/non-prototyped function declaration, you must terminate
|
|
the definition with a semi-colon (;).
|
|
.IP -
|
|
The nature of how the scanner
|
|
gets its input can be controlled by redefining the
|
|
.B YY_INPUT
|
|
macro.
|
|
YY_INPUT's calling sequence is "YY_INPUT(buf,result,max_size)". Its
|
|
action is to place up to
|
|
.I max_size
|
|
characters in the character array
|
|
.I buf
|
|
and return in the integer variable
|
|
.I result
|
|
either the
|
|
number of characters read or the constant YY_NULL (0 on Unix systems)
|
|
to indicate EOF. The default YY_INPUT reads from the
|
|
global file-pointer "yyin".
|
|
A sample redefinition of YY_INPUT (in the definitions
|
|
section of the input file):
|
|
.nf
|
|
|
|
%{
|
|
#undef YY_INPUT
|
|
#define YY_INPUT(buf,result,max_size) \\
|
|
{ \\
|
|
int c = getchar(); \\
|
|
result = (c == EOF) ? YY_NULL : (buf[0] = c, 1); \\
|
|
}
|
|
%}
|
|
|
|
.fi
|
|
.IP -
|
|
When the scanner receives an end-of-file indication from YY_INPUT,
|
|
it then checks the function
|
|
.B yywrap()
|
|
function. If
|
|
.B yywrap()
|
|
returns false (zero), then it is assumed that the
|
|
function has gone ahead and set up
|
|
.I yyin
|
|
to point to another input file, and scanning continues. If it returns
|
|
true (non-zero), then the scanner terminates, returning 0 to its
|
|
caller.
|
|
.IP
|
|
The default
|
|
.B yywrap()
|
|
always returns 1.
|
|
.IP -
|
|
YY_USER_ACTION
|
|
can be redefined to provide an action
|
|
which is always executed prior to the matched rule's action.
|
|
.IP -
|
|
The macro
|
|
.B YY_USER_INIT
|
|
may be redefined to provide an action which is always executed before
|
|
the first scan.
|
|
.IP -
|
|
In the generated scanner, the actions are all gathered in one large
|
|
switch statement and separated using
|
|
.B YY_BREAK,
|
|
which may be redefined. By default, it is simply a "break", to separate
|
|
each rule's action from the following rule's.
|
|
.SH FILES
|
|
.TP
|
|
.B \-lfl
|
|
library with which to link scanners to obtain the default versions
|
|
of
|
|
.I yywrap()
|
|
and/or
|
|
.I main().
|
|
.TP
|
|
.I lex.yy.c
|
|
generated scanner (called
|
|
.I lexyy.c
|
|
on some systems).
|
|
.TP
|
|
.I lex.yy.cc
|
|
generated C++ scanner class, when using
|
|
.B -+.
|
|
.TP
|
|
.I <FlexLexer.h>
|
|
header file defining the C++ scanner base class,
|
|
.B FlexLexer,
|
|
and its derived class,
|
|
.B yyFlexLexer.
|
|
.TP
|
|
.I flex.skl
|
|
skeleton scanner. This file is only used when building flex, not when
|
|
flex executes.
|
|
.TP
|
|
.I lex.backup
|
|
backing-up information for
|
|
.B \-b
|
|
flag (called
|
|
.I lex.bck
|
|
on some systems).
|
|
.SH "SEE ALSO"
|
|
.PP
|
|
flexdoc(1), lex(1), yacc(1), sed(1), awk(1).
|
|
.PP
|
|
M. E. Lesk and E. Schmidt,
|
|
.I LEX \- Lexical Analyzer Generator
|
|
.SH DIAGNOSTICS
|
|
.PP
|
|
.I reject_used_but_not_detected undefined
|
|
or
|
|
.PP
|
|
.I yymore_used_but_not_detected undefined -
|
|
These errors can occur at compile time. They indicate that the
|
|
scanner uses
|
|
.B REJECT
|
|
or
|
|
.B yymore()
|
|
but that
|
|
.I flex
|
|
failed to notice the fact, meaning that
|
|
.I flex
|
|
scanned the first two sections looking for occurrences of these actions
|
|
and failed to find any, but somehow you snuck some in (via a #include
|
|
file, for example). Make an explicit reference to the action in your
|
|
.I flex
|
|
input file. (Note that previously
|
|
.I flex
|
|
supported a
|
|
.B %used/%unused
|
|
mechanism for dealing with this problem; this feature is still supported
|
|
but now deprecated, and will go away soon unless the author hears from
|
|
people who can argue compellingly that they need it.)
|
|
.PP
|
|
.I flex scanner jammed -
|
|
a scanner compiled with
|
|
.B \-s
|
|
has encountered an input string which wasn't matched by
|
|
any of its rules.
|
|
.PP
|
|
.I warning, rule cannot be matched
|
|
indicates that the given rule
|
|
cannot be matched because it follows other rules that will
|
|
always match the same text as it. See
|
|
.I flexdoc(1)
|
|
for an example.
|
|
.PP
|
|
.I warning,
|
|
.B \-s
|
|
.I
|
|
option given but default rule can be matched
|
|
means that it is possible (perhaps only in a particular start condition)
|
|
that the default rule (match any single character) is the only one
|
|
that will match a particular input. Since
|
|
.PP
|
|
.I scanner input buffer overflowed -
|
|
a scanner rule matched more text than the available dynamic memory.
|
|
.PP
|
|
.I token too large, exceeds YYLMAX -
|
|
your scanner uses
|
|
.B %array
|
|
and one of its rules matched a string longer than the
|
|
.B YYLMAX
|
|
constant (8K bytes by default). You can increase the value by
|
|
#define'ing
|
|
.B YYLMAX
|
|
in the definitions section of your
|
|
.I flex
|
|
input.
|
|
.PP
|
|
.I scanner requires \-8 flag to
|
|
.I use the character 'x' -
|
|
Your scanner specification includes recognizing the 8-bit character
|
|
.I 'x'
|
|
and you did not specify the \-8 flag, and your scanner defaulted to 7-bit
|
|
because you used the
|
|
.B \-Cf
|
|
or
|
|
.B \-CF
|
|
table compression options.
|
|
.PP
|
|
.I flex scanner push-back overflow -
|
|
you used
|
|
.B unput()
|
|
to push back so much text that the scanner's buffer could not hold
|
|
both the pushed-back text and the current token in
|
|
.B yytext.
|
|
Ideally the scanner should dynamically resize the buffer in this case, but at
|
|
present it does not.
|
|
.PP
|
|
.I
|
|
input buffer overflow, can't enlarge buffer because scanner uses REJECT -
|
|
the scanner was working on matching an extremely large token and needed
|
|
to expand the input buffer. This doesn't work with scanners that use
|
|
.B
|
|
REJECT.
|
|
.PP
|
|
.I
|
|
fatal flex scanner internal error--end of buffer missed -
|
|
This can occur in an scanner which is reentered after a long-jump
|
|
has jumped out (or over) the scanner's activation frame. Before
|
|
reentering the scanner, use:
|
|
.nf
|
|
|
|
yyrestart( yyin );
|
|
|
|
.fi
|
|
or use C++ scanner classes (the
|
|
.B \-+
|
|
option), which are fully reentrant.
|
|
.SH AUTHOR
|
|
Vern Paxson, with the help of many ideas and much inspiration from
|
|
Van Jacobson. Original version by Jef Poskanzer.
|
|
.PP
|
|
See flexdoc(1) for additional credits and the address to send comments to.
|
|
.SH DEFICIENCIES / BUGS
|
|
.PP
|
|
Some trailing context
|
|
patterns cannot be properly matched and generate
|
|
warning messages ("dangerous trailing context"). These are
|
|
patterns where the ending of the
|
|
first part of the rule matches the beginning of the second
|
|
part, such as "zx*/xy*", where the 'x*' matches the 'x' at
|
|
the beginning of the trailing context. (Note that the POSIX draft
|
|
states that the text matched by such patterns is undefined.)
|
|
.PP
|
|
For some trailing context rules, parts which are actually fixed-length are
|
|
not recognized as such, leading to the abovementioned performance loss.
|
|
In particular, parts using '|' or {n} (such as "foo{3}") are always
|
|
considered variable-length.
|
|
.PP
|
|
Combining trailing context with the special '|' action can result in
|
|
.I fixed
|
|
trailing context being turned into the more expensive
|
|
.I variable
|
|
trailing context. For example, in the following:
|
|
.nf
|
|
|
|
%%
|
|
abc |
|
|
xyz/def
|
|
|
|
.fi
|
|
.PP
|
|
Use of
|
|
.B unput()
|
|
or
|
|
.B input()
|
|
invalidates yytext and yyleng, unless the
|
|
.B %array
|
|
directive
|
|
or the
|
|
.B \-l
|
|
option has been used.
|
|
.PP
|
|
Use of unput() to push back more text than was matched can
|
|
result in the pushed-back text matching a beginning-of-line ('^')
|
|
rule even though it didn't come at the beginning of the line
|
|
(though this is rare!).
|
|
.PP
|
|
Pattern-matching of NUL's is substantially slower than matching other
|
|
characters.
|
|
.PP
|
|
Dynamic resizing of the input buffer is slow, as it entails rescanning
|
|
all the text matched so far by the current (generally huge) token.
|
|
.PP
|
|
.I flex
|
|
does not generate correct #line directives for code internal
|
|
to the scanner; thus, bugs in
|
|
.I flex.skl
|
|
yield bogus line numbers.
|
|
.PP
|
|
Due to both buffering of input and read-ahead, you cannot intermix
|
|
calls to <stdio.h> routines, such as, for example,
|
|
.B getchar(),
|
|
with
|
|
.I flex
|
|
rules and expect it to work. Call
|
|
.B input()
|
|
instead.
|
|
.PP
|
|
The total table entries listed by the
|
|
.B \-v
|
|
flag excludes the number of table entries needed to determine
|
|
what rule has been matched. The number of entries is equal
|
|
to the number of DFA states if the scanner does not use
|
|
.B REJECT,
|
|
and somewhat greater than the number of states if it does.
|
|
.PP
|
|
.B REJECT
|
|
cannot be used with the
|
|
.B \-f
|
|
or
|
|
.B \-F
|
|
options.
|
|
.PP
|
|
The
|
|
.I flex
|
|
internal algorithms need documentation.
|