add directory Minix
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779
Minix/CD-ROM-2.0/MINIX/MANUALS/MAN1/FLEX.1
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Minix/CD-ROM-2.0/MINIX/MANUALS/MAN1/FLEX.1
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.TH FLEX 1 "26 May 1990" "Version 2.3"
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.SH NAME
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flex, lex - fast lexical analyzer generator
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||||
.SH SYNOPSIS
|
||||
.B flex
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||||
.B [-bcdfinpstvFILT8 -C[efmF] -Sskeleton]
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||||
.I [filename ...]
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||||
.SH DESCRIPTION
|
||||
.I flex
|
||||
is a tool for generating
|
||||
.I scanners:
|
||||
programs which recognized lexical patterns in text.
|
||||
.I flex
|
||||
reads
|
||||
the given input files, or its standard input if no file names are given,
|
||||
for a description of a scanner to generate. The description is in
|
||||
the form of pairs
|
||||
of regular expressions and C code, called
|
||||
.I rules. flex
|
||||
generates as output a C source file,
|
||||
.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
|
||||
.B -lfl
|
||||
library to produce an executable. When the executable is run,
|
||||
it analyzes its input for occurrences
|
||||
of the regular expressions. Whenever it finds one, it executes
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||||
the corresponding C code.
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.LP
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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
|
||||
.I flex
|
||||
has the following options:
|
||||
.TP
|
||||
.B -b
|
||||
Generate backtracking information to
|
||||
.I lex.backtrack.
|
||||
This is a list of scanner states which require backtracking
|
||||
and the input characters on which they do so. By adding rules one
|
||||
can remove backtracking states. If all backtracking states
|
||||
are eliminated and
|
||||
.B -f
|
||||
or
|
||||
.B -F
|
||||
is used, the generated scanner will run faster.
|
||||
.TP
|
||||
.B -c
|
||||
is a do-nothing, deprecated option included for POSIX compliance.
|
||||
.IP
|
||||
.B NOTE:
|
||||
in previous releases of
|
||||
.I flex
|
||||
.B -c
|
||||
specified table-compression options. This functionality is
|
||||
now given by the
|
||||
.B -C
|
||||
flag. To ease the the impact of this change, when
|
||||
.I flex
|
||||
encounters
|
||||
.B -c,
|
||||
it currently issues a warning message and assumes that
|
||||
.B -C
|
||||
was desired instead. In the future this "promotion" of
|
||||
.B -c
|
||||
to
|
||||
.B -C
|
||||
will go away in the name of full POSIX compliance (unless
|
||||
the POSIX meaning is removed first).
|
||||
.TP
|
||||
.B -d
|
||||
makes the generated scanner run in
|
||||
.I debug
|
||||
mode. Whenever a pattern is recognized and the global
|
||||
.B yy_flex_debug
|
||||
is non-zero (which is the default), the scanner will
|
||||
write to
|
||||
.I stderr
|
||||
a line of the form:
|
||||
.nf
|
||||
|
||||
--accepting rule at line 53 ("the matched text")
|
||||
|
||||
.fi
|
||||
The line number refers to the location of the rule in the file
|
||||
defining the scanner (i.e., the file that was fed to flex). Messages
|
||||
are also generated when the scanner backtracks, accepts the
|
||||
default rule, reaches the end of its input buffer (or encounters
|
||||
a NUL; the two look the same as far as the scanner's concerned),
|
||||
or reaches an end-of-file.
|
||||
.TP
|
||||
.B -f
|
||||
specifies (take your pick)
|
||||
.I full table
|
||||
or
|
||||
.I fast scanner.
|
||||
No table compression is done. The result is large but fast.
|
||||
This option is equivalent to
|
||||
.B -Cf
|
||||
(see below).
|
||||
.TP
|
||||
.B -i
|
||||
instructs
|
||||
.I flex
|
||||
to generate a
|
||||
.I case-insensitive
|
||||
scanner. The case of letters given in the
|
||||
.I flex
|
||||
input patterns will
|
||||
be ignored, and tokens in the input will be matched regardless of case. The
|
||||
matched text given in
|
||||
.I yytext
|
||||
will have the preserved case (i.e., it will not be folded).
|
||||
.TP
|
||||
.B -n
|
||||
is another do-nothing, deprecated option included only for
|
||||
POSIX compliance.
|
||||
.TP
|
||||
.B -p
|
||||
generates a performance report to stderr. The report
|
||||
consists of comments regarding features of the
|
||||
.I flex
|
||||
input file which will cause a loss of performance in the resulting scanner.
|
||||
.TP
|
||||
.B -s
|
||||
causes the
|
||||
.I default rule
|
||||
(that unmatched scanner input is echoed to
|
||||
.I stdout)
|
||||
to be suppressed. If the scanner encounters input that does not
|
||||
match any of its rules, it aborts with an error.
|
||||
.TP
|
||||
.B -t
|
||||
instructs
|
||||
.I flex
|
||||
to write the scanner it generates to standard output instead
|
||||
of
|
||||
.B lex.yy.c.
|
||||
.TP
|
||||
.B -v
|
||||
specifies that
|
||||
.I flex
|
||||
should write to
|
||||
.I stderr
|
||||
a summary of statistics regarding the scanner it generates.
|
||||
.TP
|
||||
.B -F
|
||||
specifies that the
|
||||
.I fast
|
||||
scanner table representation should be used. This representation is
|
||||
about as fast as the full table representation
|
||||
.RB ( \-f ),
|
||||
and for some sets of patterns will be considerably smaller (and for
|
||||
others, larger). See
|
||||
.B flexdoc(1)
|
||||
for details.
|
||||
.IP
|
||||
This option is equivalent to
|
||||
.B -CF
|
||||
(see below).
|
||||
.TP
|
||||
.B -I
|
||||
instructs
|
||||
.I flex
|
||||
to generate an
|
||||
.I interactive
|
||||
scanner, that is, a scanner which stops immediately rather than
|
||||
looking ahead if it knows
|
||||
that the currently scanned text cannot be part of a longer rule's match.
|
||||
Again, see
|
||||
.B flexdoc(1)
|
||||
for details.
|
||||
.IP
|
||||
Note,
|
||||
.B -I
|
||||
cannot be used in conjunction with
|
||||
.I full
|
||||
or
|
||||
.I fast tables,
|
||||
i.e., the
|
||||
.B -f, -F, -Cf,
|
||||
or
|
||||
.B -CF
|
||||
flags.
|
||||
.TP
|
||||
.B -L
|
||||
instructs
|
||||
.I flex
|
||||
not to generate
|
||||
.B #line
|
||||
directives in
|
||||
.B lex.yy.c.
|
||||
The default is to generate such directives so error
|
||||
messages in the actions will be correctly
|
||||
located with respect to the original
|
||||
.I flex
|
||||
input file, and not to
|
||||
the fairly meaningless line numbers of
|
||||
.B lex.yy.c.
|
||||
.TP
|
||||
.B -T
|
||||
makes
|
||||
.I flex
|
||||
run in
|
||||
.I trace
|
||||
mode. It will generate a lot of messages to
|
||||
.I stdout
|
||||
concerning
|
||||
the form of the input and the resultant non-deterministic and deterministic
|
||||
finite automata. This option is mostly for use in maintaining
|
||||
.I flex.
|
||||
.TP
|
||||
.B -8
|
||||
instructs
|
||||
.I flex
|
||||
to generate an 8-bit scanner.
|
||||
On some sites, this is the default. On others, the default
|
||||
is 7-bit characters. To see which is the case, check the verbose
|
||||
.B (-v)
|
||||
output for "equivalence classes created". If the denominator of
|
||||
the number shown is 128, then by default
|
||||
.I flex
|
||||
is generating 7-bit characters. If it is 256, then the default is
|
||||
8-bit characters.
|
||||
.TP
|
||||
.B -C[efmF]
|
||||
controls the degree of table compression.
|
||||
.IP
|
||||
.B -Ce
|
||||
directs
|
||||
.I flex
|
||||
to construct
|
||||
.I equivalence classes,
|
||||
i.e., sets of characters
|
||||
which have identical lexical properties.
|
||||
Equivalence classes usually give
|
||||
dramatic reductions in the final table/object file sizes (typically
|
||||
a factor of 2-5) and are pretty cheap performance-wise (one array
|
||||
look-up per character scanned).
|
||||
.IP
|
||||
.B -Cf
|
||||
specifies that the
|
||||
.I full
|
||||
scanner tables should be generated -
|
||||
.I flex
|
||||
should not compress the
|
||||
tables by taking advantages of similar transition functions for
|
||||
different states.
|
||||
.IP
|
||||
.B -CF
|
||||
specifies that the alternate fast scanner representation (described in
|
||||
.B flexdoc(1))
|
||||
should be used.
|
||||
.IP
|
||||
.B -Cm
|
||||
directs
|
||||
.I flex
|
||||
to construct
|
||||
.I meta-equivalence classes,
|
||||
which are sets of equivalence classes (or characters, if equivalence
|
||||
classes are not being used) that are commonly used together. Meta-equivalence
|
||||
classes are often a big win when using compressed tables, but they
|
||||
have a moderate performance impact (one or two "if" tests and one
|
||||
array look-up per character scanned).
|
||||
.IP
|
||||
A lone
|
||||
.B -C
|
||||
specifies that the scanner tables should be compressed but neither
|
||||
equivalence classes nor meta-equivalence classes should be used.
|
||||
.IP
|
||||
The options
|
||||
.B -Cf
|
||||
or
|
||||
.B -CF
|
||||
and
|
||||
.B -Cm
|
||||
do not make sense together - there is no opportunity for meta-equivalence
|
||||
classes if the table is not being compressed. Otherwise the options
|
||||
may be freely mixed.
|
||||
.IP
|
||||
The default setting is
|
||||
.B -Cem,
|
||||
which specifies that
|
||||
.I flex
|
||||
should generate equivalence classes
|
||||
and meta-equivalence classes. This setting provides the highest
|
||||
degree of table compression. You can trade off
|
||||
faster-executing scanners at the cost of larger tables with
|
||||
the following generally being true:
|
||||
.nf
|
||||
|
||||
slowest & smallest
|
||||
-Cem
|
||||
-Cm
|
||||
-Ce
|
||||
-C
|
||||
-C{f,F}e
|
||||
-C{f,F}
|
||||
fastest & largest
|
||||
|
||||
.fi
|
||||
.IP
|
||||
.B -C
|
||||
options are not cumulative; whenever the flag is encountered, the
|
||||
previous -C settings are forgotten.
|
||||
.TP
|
||||
.B -Sskeleton_file
|
||||
overrides the default skeleton file from which
|
||||
.I flex
|
||||
constructs its scanners. You'll never need this option unless you are doing
|
||||
.I flex
|
||||
maintenance or development.
|
||||
.SH SUMMARY OF FLEX REGULAR EXPRESSIONS
|
||||
The patterns in the input are written using an extended set of regular
|
||||
expressions. These are:
|
||||
.nf
|
||||
|
||||
x match the character 'x'
|
||||
. any character except newline
|
||||
[xyz] a "character class"; in this case, the pattern
|
||||
matches either an 'x', a 'y', or a 'z'
|
||||
[abj-oZ] a "character class" with a range in it; matches
|
||||
an 'a', a 'b', any letter from 'j' through 'o',
|
||||
or a 'Z'
|
||||
[^A-Z] a "negated character class", i.e., any character
|
||||
but those in the class. In this case, any
|
||||
character EXCEPT an uppercase letter.
|
||||
[^A-Z\\n] any character EXCEPT an uppercase letter or
|
||||
a newline
|
||||
r* zero or more r's, where r is any regular expression
|
||||
r+ one or more r's
|
||||
r? zero or one r's (that is, "an optional r")
|
||||
r{2,5} anywhere from two to five r's
|
||||
r{2,} two or more r's
|
||||
r{4} exactly 4 r's
|
||||
{name} the expansion of the "name" definition
|
||||
(see above)
|
||||
"[xyz]\\"foo"
|
||||
the literal string: [xyz]"foo
|
||||
\\X if X is an 'a', 'b', 'f', 'n', 'r', 't', or 'v',
|
||||
then the ANSI-C interpretation of \\x.
|
||||
Otherwise, a literal 'X' (used to escape
|
||||
operators such as '*')
|
||||
\\123 the character with octal value 123
|
||||
\\x2a the character with hexadecimal value 2a
|
||||
(r) match an r; parentheses are used to override
|
||||
precedence (see below)
|
||||
|
||||
|
||||
rs the regular expression r followed by the
|
||||
regular expression s; called "concatenation"
|
||||
|
||||
|
||||
r|s either an r or an s
|
||||
|
||||
|
||||
r/s an r but only if it is followed by an s. The
|
||||
s is not part of the matched text. This type
|
||||
of pattern is called as "trailing context".
|
||||
^r an r, but only at the beginning of a line
|
||||
r$ an r, but only at the end of a line. Equivalent
|
||||
to "r/\\n".
|
||||
|
||||
|
||||
<s>r an r, but only in start condition s (see
|
||||
below for discussion of start conditions)
|
||||
<s1,s2,s3>r
|
||||
same, but in any of start conditions s1,
|
||||
s2, or s3
|
||||
|
||||
|
||||
<<EOF>> an end-of-file
|
||||
<s1,s2><<EOF>>
|
||||
an end-of-file when in start condition s1 or s2
|
||||
|
||||
.fi
|
||||
The regular expressions listed above are grouped according to
|
||||
precedence, from highest precedence at the top to lowest at the bottom.
|
||||
Those grouped together have equal precedence.
|
||||
.LP
|
||||
Some notes on patterns:
|
||||
.IP -
|
||||
Negated character classes
|
||||
.I match newlines
|
||||
unless "\\n" (or an equivalent escape sequence) is one of the
|
||||
characters explicitly present in the negated character class
|
||||
(e.g., "[^A-Z\\n]").
|
||||
.IP -
|
||||
A rule can have at most one instance of trailing context (the '/' operator
|
||||
or the '$' operator). The start condition, '^', and "<<EOF>>" patterns
|
||||
can only occur at the beginning of a pattern, and, as well as with '/' and '$',
|
||||
cannot be grouped inside parentheses. The following are all illegal:
|
||||
.nf
|
||||
|
||||
foo/bar$
|
||||
foo|(bar$)
|
||||
foo|^bar
|
||||
<sc1>foo<sc2>bar
|
||||
|
||||
.fi
|
||||
.SH SUMMARY OF SPECIAL ACTIONS
|
||||
In addition to arbitrary C code, the following can appear in actions:
|
||||
.IP -
|
||||
.B ECHO
|
||||
copies yytext to the scanner's output.
|
||||
.IP -
|
||||
.B BEGIN
|
||||
followed by the name of a start condition places the scanner in the
|
||||
corresponding start condition.
|
||||
.IP -
|
||||
.B REJECT
|
||||
directs the scanner to proceed on to the "second best" rule which matched the
|
||||
input (or a prefix of the input).
|
||||
.B yytext
|
||||
and
|
||||
.B yyleng
|
||||
are set up appropriately. Note that
|
||||
.B REJECT
|
||||
is a particularly expensive feature in terms scanner performance;
|
||||
if it is used in
|
||||
.I any
|
||||
of the scanner's actions it will slow down
|
||||
.I all
|
||||
of the scanner's matching. Furthermore,
|
||||
.B REJECT
|
||||
cannot be used with the
|
||||
.I -f
|
||||
or
|
||||
.I -F
|
||||
options.
|
||||
.IP
|
||||
Note also that unlike the other special actions,
|
||||
.B REJECT
|
||||
is a
|
||||
.I branch;
|
||||
code immediately following it in the action will
|
||||
.I not
|
||||
be executed.
|
||||
.IP -
|
||||
.B yymore()
|
||||
tells the scanner that the next time it matches a rule, the corresponding
|
||||
token should be
|
||||
.I appended
|
||||
onto the current value of
|
||||
.B yytext
|
||||
rather than replacing it.
|
||||
.IP -
|
||||
.B yyless(n)
|
||||
returns all but the first
|
||||
.I n
|
||||
characters of the current token back to the input stream, where they
|
||||
will be rescanned when the scanner looks for the next match.
|
||||
.B yytext
|
||||
and
|
||||
.B yyleng
|
||||
are adjusted appropriately (e.g.,
|
||||
.B yyleng
|
||||
will now be equal to
|
||||
.I n
|
||||
).
|
||||
.IP -
|
||||
.B unput(c)
|
||||
puts the character
|
||||
.I c
|
||||
back onto the input stream. It will be the next character scanned.
|
||||
.IP -
|
||||
.B input()
|
||||
reads the next character from the input stream (this routine is called
|
||||
.B yyinput()
|
||||
if the scanner is compiled using
|
||||
.B C++).
|
||||
.IP -
|
||||
.B yyterminate()
|
||||
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".
|
||||
.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 not be modified.
|
||||
.IP -
|
||||
.B int yyleng
|
||||
holds the length of the current token. It may not be modified.
|
||||
.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. Changing it in the middle of scanning will have
|
||||
unexpected results since
|
||||
.I flex
|
||||
buffers its input. Once scanning terminates because an end-of-file
|
||||
has been seen,
|
||||
.B
|
||||
void yyrestart( FILE *new_file )
|
||||
may be called to point
|
||||
.I yyin
|
||||
at the new 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.
|
||||
.SH MACROS THE USER 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
|
||||
.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. Presently, to redefine it you must first
|
||||
"#undef yywrap", as it is currently implemented as a macro. It is
|
||||
likely that
|
||||
.B yywrap()
|
||||
will soon be defined to be a function rather than a macro.
|
||||
.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
|
||||
.I flex.skel
|
||||
skeleton scanner.
|
||||
.TP
|
||||
.I lex.yy.c
|
||||
generated scanner (called
|
||||
.I lexyy.c
|
||||
on some systems).
|
||||
.TP
|
||||
.I lex.backtrack
|
||||
backtracking information for
|
||||
.B -b
|
||||
flag (called
|
||||
.I lex.bck
|
||||
on some systems).
|
||||
.TP
|
||||
.B -lfl
|
||||
library with which to link the scanners.
|
||||
.SH "SEE ALSO"
|
||||
.LP
|
||||
flexdoc(1), lex(1), yacc(1), sed(1), awk(1).
|
||||
.LP
|
||||
M. E. Lesk and E. Schmidt,
|
||||
.I LEX - Lexical Analyzer Generator
|
||||
.SH DIAGNOSTICS
|
||||
.I reject_used_but_not_detected undefined
|
||||
or
|
||||
.LP
|
||||
.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.)
|
||||
.LP
|
||||
.I flex scanner jammed -
|
||||
a scanner compiled with
|
||||
.B -s
|
||||
has encountered an input string which wasn't matched by
|
||||
any of its rules.
|
||||
.LP
|
||||
.I flex input buffer overflowed -
|
||||
a scanner rule matched a string long enough to overflow the
|
||||
scanner's internal input buffer (16K bytes - controlled by
|
||||
.B YY_BUF_MAX
|
||||
in "flex.skel").
|
||||
.LP
|
||||
.I scanner requires -8 flag -
|
||||
Your scanner specification includes recognizing 8-bit characters and
|
||||
you did not specify the -8 flag (and your site has not installed flex
|
||||
with -8 as the default).
|
||||
.LP
|
||||
.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
|
||||
.LP
|
||||
.I too many %t classes! -
|
||||
You managed to put every single character into its own %t class.
|
||||
.I flex
|
||||
requires that at least one of the classes share characters.
|
||||
.SH AUTHOR
|
||||
Vern Paxson, with the help of many ideas and much inspiration from
|
||||
Van Jacobson. Original version by Jef Poskanzer.
|
||||
.LP
|
||||
See flexdoc(1) for additional credits and the address to send comments to.
|
||||
.SH DEFICIENCIES / BUGS
|
||||
.LP
|
||||
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.)
|
||||
.LP
|
||||
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.
|
||||
.LP
|
||||
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, this happens in the following example:
|
||||
.nf
|
||||
|
||||
%%
|
||||
abc |
|
||||
xyz/def
|
||||
|
||||
.fi
|
||||
.LP
|
||||
Use of unput() invalidates yytext and yyleng.
|
||||
.LP
|
||||
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!).
|
||||
.LP
|
||||
Pattern-matching of NUL's is substantially slower than matching other
|
||||
characters.
|
||||
.LP
|
||||
.I flex
|
||||
does not generate correct #line directives for code internal
|
||||
to the scanner; thus, bugs in
|
||||
.I flex.skel
|
||||
yield bogus line numbers.
|
||||
.LP
|
||||
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.
|
||||
.LP
|
||||
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.
|
||||
.LP
|
||||
.B REJECT
|
||||
cannot be used with the
|
||||
.I -f
|
||||
or
|
||||
.I -F
|
||||
options.
|
||||
.LP
|
||||
Some of the macros, such as
|
||||
.B yywrap(),
|
||||
may in the future become functions which live in the
|
||||
.B -lfl
|
||||
library. This will doubtless break a lot of code, but may be
|
||||
required for POSIX-compliance.
|
||||
.LP
|
||||
The
|
||||
.I flex
|
||||
internal algorithms need documentation.
|
||||
Reference in New Issue
Block a user