RE2C(1)RE2C(1)
NAME
re2c - convert regular expressions to C/C++ code
SYNOPSIS
re2c [OPTIONS] INPUT_FILE [-o OUTPUT_FILE]
DESCRIPTION
Re2c is a lexer generator for C/C++. It finds regular expression speci-
fications inside of C/C++ comments and compiles them to a deterministic
finite state machine. The user should write some interface code in or-
der to bind the generated lexer to the program environment. Sections
EOF handling and buffer refilling explain how the generated lexer
checks for the end of input and (if necessary) asks for more input.
Various re2c features are described in sections include files, header
files, submatch extraction, storable state, reusable blocks, encoding
support, start conditions, skeleton programs and visualization and de-
bug. Re2c provides a lot of options, configurations and directives
that allow one to customize the generated code.
OPTIONS
-? -h --help
Show help message.
-1 --single-pass
Deprecated. Does nothing (single pass is the default now).
-8 --utf-8
Generate a lexer that reads input in UTF-8 encoding. re2c as-
sumes that character range is 0 -- 0x10FFFF and character size
is 1 byte.
-b --bit-vectors
Optimize conditional jumps using bit masks. Implies -s.
-c --conditions --start-conditions
Enable support of Flex-like "conditions": multiple interrelated
lexers within one block. Option --start-conditions is a legacy
alias; use --conditions instead.
--case-insensitive
Treat single-quoted and double-quoted strings as case-insensi-
tive.
--case-inverted
Invert the meaning of single-quoted and double-quoted strings:
treat single-quoted strings as case-sensitive and double-quoted
strings as case-insensitive.
-D --emit-dot
Instead of normal output generate lexer graph in .dot format.
The output can be converted to an image with the help of
Graphviz (e.g. something like dot -Tpng -odfa.png dfa.dot).
-d --debug-output
Emit YYDEBUG in the generated code. YYDEBUG should be defined
by the user in the form of a void function with two parameters:
state (lexer state or -1) and symbol (current input symbol of
type YYCTYPE).
--dfa-minimization <moore | table>
The internal algorithm used by re2c to minimize the DFA: moore
(the default) is Moore algorithm, and table is the "table fill-
ing" algorithm. Both algorithms should produce the same DFA up
to states relabeling; table filling is simpler and much slower
and serves as a reference implementation.
--dump-adfa
Debug option: output DFA after tunneling (in .dot format).
--dump-cfg
Debug option: output control flow graph of tag variables (in
.dot format).
--dump-closure-stats
Debug option: output statistics on the number of states in clo-
sure.
--dump-dfa-det
Debug option: output DFA immediately after determinization (in
.dot format).
--dump-dfa-min
Debug option: output DFA after minimization (in .dot format).
--dump-dfa-tagopt
Debug option: output DFA after tag optimizations (in .dot for-
mat).
--dump-dfa-raw
Debug option: output DFA under construction with expanded
state-sets (in .dot format).
--dump-interf
Debug option: output interference table produced by liveness
analysis of tag variables.
--dump-nfa
Debug option: output NFA (in .dot format).
-e --ecb
Generate a lexer that reads input in EBCDIC encoding. re2c as-
sumes that character range is 0 -- 0xFF an character size is 1
byte.
--eager-skip
Make the generated lexer advance the input position "eagerly":
immediately after reading input symbol. By default this happens
after transition to the next state. Implied by --no-lookahead.
--empty-class <match-empty | match-none | error>
Define the way re2c treats empty character classes. With
match-empty (the default) empty class matches empty input (which
is illogical, but backwards-compatible). With``match-none``
empty class always fails to match. With error empty class
raises a compilation error.
--encoding-policy <fail | substitute | ignore>
Define the way re2c treats Unicode surrogates. With fail re2c
aborts with an error when a surrogate is encountered. With sub-
stitute re2c silently replaces surrogates with the error code
point 0xFFFD. With ignore (the default) re2c treats surrogates
as normal code points. The Unicode standard says that standalone
surrogates are invalid, but real-world libraries and programs
behave in different ways.
-f --storable-state
Generate a lexer which can store its inner state. This is use-
ful in push-model lexers which are stopped by an outer program
when there is not enough input, and then resumed when more input
becomes available. In this mode users should additionally define
YYGETSTATE() and YYSETSTATE(state) macros and variables yych,
yyaccept and state as part of the lexer state.
-F --flex-syntax
Partial support for Flex syntax: in this mode named definitions
don't need the equal sign and the terminating semicolon, and
when used they must be surrounded by curly braces. Names without
curly braces are treated as double-quoted strings.
-g --computed-gotos
Optimize conditional jumps using non-standard "computed goto"
extension (which must be supported by the C/C++ compiler). re2c
generates jump tables only in complex cases with a lot of condi-
tional branches. Complexity threshold can be configured with
cgoto:threshold configuration. This option implies -b.
-I PATH
Add PATH to the list of locations which are used when searching
for include files. This option is useful in combination with
/*!include:re2c ... */ directive. Re2c looks for FILE in the di-
rectory of including file and in the list of include paths spec-
ified by -I option.
-i --no-debug-info
Do not output #line information. This is useful when the gener-
ated code is tracked by some version control system or IDE.
--input <default | custom>
Specify re2c input API. Option default is the default API com-
posed of pointer-like primitives YYCURSOR, YYMARKER, YYLIMIT
etc. Option custom is the generic API composed of function-like
primitives YYPEEK(), YYSKIP(), YYBACKUP(), YYRESTORE() etc.
--input-encoding <ascii | utf8>
Specify the way re2c parses regular expressions. With ascii
(the default) re2c handles input as ASCII-encoded: any sequence
of code units is a sequence of standalone 1-byte characters.
With utf8 re2c handles input as UTF8-encoded and recognizes
multibyte characters.
--location-format <gnu | msvc>
Specify location format in messages. With gnu locations are
printed as 'filename:line:column: ...'. With msvc locations are
printed as 'filename(line,column) ...'. Default is gnu.
--no-generation-date
Suppress date output in the generated file.
--no-lookahead
Use TDFA(0) instead of TDFA(1). This option has effect only
with --tags or --posix-captures options.
--no-optimize-tags
Suppress optimization of tag variables (useful for debugging).
--no-version
Suppress version output in the generated file.
-o OUTPUT --output=OUTPUT
Specify the OUTPUT file.
-P --posix-captures
Enable submatch extraction with POSIX-style capturing groups.
--posix-closure <gor1 | gtop>
Specify shortest-path algorithm used for construction of ep-
silon-closure with POSIX disambiguation semantics: gor1 (the de-
fault) stands for Goldberg-Radzik algorithm, and gtop stands for
"global topological order" algorithm.
-r --reusable
Allows reuse of re2c rules with /*!rules:re2c */ and /*!use:re2c
*/ blocks. Exactly one rules-block must be present. The rules
are saved and used by every use-block that follows, which may
add its own rules and configurations.
-S --skeleton
Ignore user-defined interface code and generate a self-contained
"skeleton" program. Additionally, generate input files with
strings derived from the regular grammar and compressed match
results that are used to verify "skeleton" behavior on all in-
puts. This option is useful for finding bugs in optimizations
and code generation.
-s --nested-ifs
Use nested if statements instead of switch statements in condi-
tional jumps. This usually results in more efficient code with
non-optimizing C/C++ compilers.
--stadfa
Use staDFA algorithm for submatch extraction. The main differ-
ence with TDFA is that tag operations in staDFA are placed in
states, not on transitions.
-T --tags
Enable submatch extraction with tags.
-t HEADER --type-header=HEADER
Generate a HEADER file that contains enum with condition names.
Requires -c option.
-u --unicode
Generate a lexer that reads UTF32-encoded input. Re2c assumes
that character range is 0 -- 0x10FFFF and character size is 4
bytes. This option implies -s.
-V --vernum
Show version information in MMmmpp format (major, minor, patch).
--verbose
Output a short message in case of success.
-v --version
Show version information.
-w --wide-chars
Generate a lexer that reads UCS2-encoded input. Re2c assumes
that character range is 0 -- 0xFFFF and character size is 2
bytes. This option implies -s.
-x --utf-16
Generate a lexer that reads UTF16-encoded input. Re2c assumes
that character range is 0 -- 0x10FFFF and character size is 2
bytes. This option implies -s.
WARNINGS
-W Turn on all warnings.
-Werror
Turn warnings into errors. Note that this option alone doesn't
turn on any warnings; it only affects those warnings that have
been turned on so far or will be turned on later.
-W<warning>
Turn on warning.
-Wno-<warning>
Turn off warning.
-Werror-<warning>
Turn on warning and treat it as an error (this implies -W<warn-
ing>).
-Wno-error-<warning>
Don't treat this particular warning as an error. This doesn't
turn off the warning itself.
-Wcondition-order
Warn if the generated program makes implicit assumptions about
condition numbering. One should use either the -t, --type-header
option or the /*!types:re2c*/ directive to generate a mapping of
condition names to numbers and then use the autogenerated condi-
tion names.
-Wempty-character-class
Warn if a regular expression contains an empty character class.
Trying to match an empty character class makes no sense: it
should always fail. However, for backwards compatibility rea-
sons re2c allows empty character classes and treats them as
empty strings. Use the --empty-class option to change the de-
fault behavior.
-Wmatch-empty-string
Warn if a rule is nullable (matches an empty string). If the
lexer runs in a loop and the empty match is unintentional, the
lexer may unexpectedly hang in an infinite loop.
-Wswapped-range
Warn if the lower bound of a range is greater than its upper
bound. The default behavior is to silently swap the range
bounds.
-Wundefined-control-flow
Warn if some input strings cause undefined control flow in the
lexer (the faulty patterns are reported). This is the most dan-
gerous and most common mistake. It can be easily fixed by adding
the default rule * which has the lowest priority, matches any
code unit, and consumes exactly one code unit.
-Wunreachable-rules
Warn about rules that are shadowed by other rules and will never
match.
-Wuseless-escape
Warn if a symbol is escaped when it shouldn't be. By default,
re2c silently ignores such escapes, but this may as well indi-
cate a typo or an error in the escape sequence.
-Wnondeterministic-tags
Warn if a tag has n-th degree of nondeterminism, where n is
greater than 1.
-Wsentinel-in-midrule
Warn if the sentinel symbol occurs in the middle of a rule ---
this may cause reads past the end of buffer, crashes or memory
corruption in the generated lexer. This warning is only applica-
ble if the sentinel method of checking for the end of input is
used. It is set to an error if re2c:sentinel configuration is
used.
SYNTAX
A re2c program consists of a number of re2c blocks and directives in-
termixed with normal C/C++ code. Each re2c block consists of a sequence
of named definitions, configurations and rules that contain regular ex-
pressions. The generated lexer communicates with the outer world by the
means of user interface. Rules consist of a regular expression fol-
lowed by a user-defined action (semantic action): a block of C/C++ code
that is executed in case of successful match. Semantic action can be
either an arbitrary block of code enclosed in curly braces { and }, or
a block of code without curly braces preceded with := and ended with a
newline that is not followed by a whitespace. If multiple rules match,
longest match takes precedence. If multiple rules match the same
string, the earlier rule takes priority. If -c --conditions option is
used, then rules have more complex form described in the section about
conditions. There are two special kinds of rules:
o Default rule * which has the lowest priority reagrdless of its place
in the source code, matches any code unit and consumes exactly one
code unit. This rule should always be defined.
o EOF rule $ which matches the end of input. This rule should be de-
fined if the simplified EOF handling method is used.
Named definitions are of the form name = regexp ; where name is an
identifier that consists of letters, digits and underscores, and regexp
is a regular expression. With -F --flex-syntax option named definitions
are also of the form name regexp. Each name should be defined before it
is used.
REGULAR EXPRESSIONS
re2c uses the following syntax for regular expressions:
o "foo" case-sensitive string literal
o 'foo' case-insensitive string literal
o [a-xyz], [^a-xyz] character class (possibly negated)
o . any character except newline
o R \ S difference of character classes R and S
o R* zero or more occurrences of R
o R+ one or more occurrences of R
o R? optional R
o R{n} repetition of R exactly n times
o R{n,} repetition of R at least n times
o R{n,m} repetition of R from n to m times
o (R) just R; parentheses are used to override precedence or for
POSIX-style submatch
o R S concatenation: R followed by S
o R | S alternative: R or S
o R / S lookahead: R followed by S, but S is not consumed
o name the regular expression defined as name (or literal string "name"
in Flex compatibility mode)
o {name} the regular expression defined as name in Flex compatibility
mode
o @stag an s-tag: saves the last input position at which @stag matches
in a variable named stag
o #mtag an m-tag: saves all input positions at which #mtag matches in a
variable named mtag
Character classes and string literals may contain the following escape
sequences: \a, \b, \f, \n, \r, \t, \v, \\, octal escapes \ooo and hexa-
decimal escapes \xhh, \uhhhh and \Uhhhhhhhh.
INTERFACE CODE
Below is the list of all symbols which may be used by the lexer in or-
der to interact with the outer world. These symbols should be defined
by the user, either in the form of inplace configurations, or as C/C++
variables, functions, macros and other language constructs. Which
primitives are necessary depends on the particular use case.
yyaccept
L-value of unsigned integral type that is used to hold the num-
ber of the last matched rule. Explicit definition by the user
is necessary only with -f --storable-state option.
YYBACKUP ()
Backup current input position (used only with --input custom op-
tion).
YYBACKUPCTX ()
Backup current input position for trailing context (used only
with --input custom option).
yych L-value of type YYCTYPE that is used to hold current input char-
acter. Explicit definition by the user is necessary only with
-f --storable-state option.
YYCONDTYPE
The type of condition identifiers (used only with -c --condi-
tions option). Should be generated either with /*!types:re2c*/
directive, or with -t --type-header option.
YYCTXMARKER
L-value of type YYCTYPE * that is used to backup input position
of trailing context. It is needed only if regular expressions
use the lookahead operator /.
YYCTYPE
The type of the input characters (code units). Usually it
should be unsigned char for ASCII, EBCDIC and UTF-8 encodings,
unsigned short for UTF-16 or UCS-2 encodings, and unsigned int
for UTF-32 encoding.
YYCURSOR
L-value of type YYCTYPE * that is used as a pointer to the cur-
rent input symbol. Initially YYCURSOR points to the first char-
acter and is advanced by the lexer during matching. When a rule
matches, YYCURSOR points past the last character of the matched
string.
YYDEBUG (state, symbol)
A function-like primitive that is used to dump debug information
(only used with -d --debug-output option). YYDEBUG should re-
turn no value and accept two arguments: state (either lexer
state or -1) and symbol (current input symbol).
YYFILL (n)
A function-like primitive that is called by the lexer when there
is not enough input. YYFILL should return no value and supply
at least n additional characters. Maximal value of n equals YY-
MAXFILL, which can be obtained with the /*!max:re2c*/ directive.
YYGETCONDITION ()
R-value of type YYCONDTYPE that represents current condition
identifier (used only with -c --conditions option).
YYGETSTATE ()
R-value of signed integral type that represents current lexer
state (used only with -f --storable-state option). Initial
value of lexer state should be -1.
YYLESSTHAN (n)
R-value of boolean type that is true if and only if there is
less than n input characters left (used only with --input cus-
tom option).
YYLIMIT
R-value of type YYCTYPE * that marks the end of input
(YYLIMIT[-1] should be the last input character). Lexer com-
pares YYCURSOR and YYLIMIT in order to determine if there is
enough input characters left.
YYMARKER
L-value of type YYCTYPE * used to backup input position of suc-
cessful match. This might be necessary if there is an overlap-
ping longer rule that might also match.
YYMTAGP (t)
Append current input position to the history of m-tag t (used
only with -T --tags option).
YYMTAGPD (t)
Same as YYMTAGP, except that instead of the current position it
should save the one before it. This is used for staDFA "delayed
store" actions.
YYMTAGN (t)
Append default value to the history of m-tag t (used only with
-T --tags option).
YYMAXFILL
Integral constant that denotes maximal value of YYFILL argument
and is autogenerated by /*!max:re2c*/ directive.
YYMAXNMATCH
Integral constant that denotes maximal number of capturing
groups in a rule and is autogenerated by /*!maxnmatch:re2c*/ di-
rective (used only with --posix-captures option).
yynmatch
L-value of unsigned integral type that is used to hold the num-
ber of capturing groups in the matching rule. Used only with -P
--posix-captures option.
YYPEEK ()
R-value of type YYCTYPE that denotes current input character
(used only with --input custom option).
yypmatch
An array of l-values that are used to hold the values of s-tags
corresponding to the capturing parentheses in the matching rule.
The length of array must be at least yynmatch * 2 (ideally YY-
MAXNMATCH * 2). Used only with -P --posix-captures option.
YYRESTORE ()
Restore input position (used only with --input custom option).
YYRESTORECTX ()
Restore input position from the value of trailing context (used
only with --input custom option).
YYRESTORETAG (t)
Restore input position from the value of s-tag t (used only with
--input custom option).
YYSETCONDITION (condition)
Set current condition identifier to condition (used only with -c
--conditions option).
YYSETSTATE (state)
Set current lexer state to state (used only with -f
--storable-state option). Parameter state is of signed integral
type.
YYSKIP ()
Advance input position to the next character (used only with
generic API).
YYSTAGP (t)
Save current input position to s-tag t (used only with -T --tags
and --input custom option).
YYSTAGPD (t)
Same as YYSTAGP, except that instead of the current position it
should save the one before it. This is used for staDFA "delayed
store" actions.
YYSTAGN (t)
Save default value to s-tag t (used only with -T --tags and
--input custom options).
Default API
By default re2c operates on input using pointer-like primitives YYCUR-
SOR, YYMARKER, YYCTXMARKER, and YYLIMIT. Normally pointer-like primi-
tives are defined as variables of type YYCTYPE*, but it is possible to
use STL iterators or any other abstraction as long as it syntactically
fits into the following use cases:
o ++YYCURSOR;
o yych = *YYCURSOR;
o yych = *++YYCURSOR;
o yych = *(YYMARKER = YYCURSOR);
o yych = *(YYMARKER = ++YCURSOR);
o YYMARKER = YYCURSOR;
o YYMARKER = ++YYCURSOR;
o YYCURSOR = YYMARKER;
o YYCTXMARKER = YYCURSOR + 1;
o YYCURSOR = YYCTXMARKER;
o if (YYLIMIT <= YYCURSOR) ...
o if ((YYLIMIT - YYCURSOR) < n) ...
o YYDEBUG (label, *YYCURSOR);
Generic API
If the default input model is too restrictive, then it is possible to
use generic input API enabled with --input custom option. In this mode
all input operations are expressed in terms of the primitives below.
These primitives can be defined in any suitable way; one doesn't have
to stick to the pointer semantics. For example, it is possible to read
input directly from file without any buffering, or to disable YYFILL
mechanism and perform end-of-input checking on each input character
from inside of YYPEEK or YYSKIP.
o YYPEEK ()
o YYSKIP ()
o YYBACKUP ()
o YYBACKUPCTX ()
o YYSTAGP (t)
o YYSTAGPD (t)
o YYSTAGN (t)
o YYMTAGP (t)
o YYMTAGPD (t)
o YYMTAGN (t)
o YYRESTORE ()
o YYRESTORECTX ()
o YYRESTORETAG (t)
o YYLESSTHAN (n)
Default input model can be expressed in terms of generic API as follows
(except for YMTAGP, YYMTAGPD and YYMTAGN, which have no default imple-
mentation):
#define YYPEEK () *YYCURSOR
#define YYSKIP () ++YYCURSOR
#define YYBACKUP () YYMARKER = YYCURSOR
#define YYBACKUPCTX () YYCTXMARKER = YYCURSOR
#define YYRESTORE () YYCURSOR = YYMARKER
#define YYRESTORECTX () YYCURSOR = YYCTXMARKER
#define YYRESTORERAG (t) YYCURSOR = t
#define YYLESSTHAN (n) YYLIMIT - YYCURSOR < n
#define YYSTAGP (t) t = YYCURSOR
#define YYSTAGPD (t) t = YYCURSOR - 1
#define YYSTAGN (t) t = NULL
DIRECTIVES
Below is the list of all directives provided by re2c (in no particular
order). More information on each directive can be found in the related
sections.
/*!re2c ... */
A standard re2c block.
%{ ... %}
A standard re2c block in -F --flex-support mode.
/*!rules:re2c ... */
A reusable re2c block (requires -r --reuse option).
/*!use:re2c ... */
A block that reuses previous rules-block specified with
/*!rules:re2c ... */ (requires -r --reuse option).
/*!ignore:re2c ... */
A block which contents are ignored and cut off from the output
file.
/*!max:re2c*/
This directive is substituted with the macro-definition of YY-
MAXFILL.
/*!maxnmatch:re2c*/
This directive is substituted with the macro-definition of YY-
MAXNMATCH (requires -P --posix-captures option).
/*!getstate:re2c*/
This directive is substituted with conditional dispatch on lexer
state (requires -f --storable-state option).
/*!types:re2c ... */
This directive is substituted with the definition of condition
enum (requires -c --conditions option).
/*!stags:re2c ... */, /*!mtags:re2c ... */
These directives allow one to specify a template piece of code
that is expanded for each s-tag/m-tag variable generated by
re2c. This block has two optional configurations: format = "@@";
(specifies the template where @@ is substituted with the name of
each tag variable), and separator = ""; (specifies the piece of
code used to join the generated pieces for different tag vari-
ables).
/*!include:re2c FILE */
This directive allows one to include FILE (in the same sense as
#include directive in C/C++).
/*!header:re2c:on*/
This directive marks the start of header file. Everything after
it and up to the following /*!header:re2c:off*/ directive is
processed by re2c and written to the header file specified with
-t --type-header option.
/*!header:re2c:off*/
This directive marks the end of header file started with
/*!header:re2c:on*/.
CONFIGURATIONS
re2c:cgoto:threshold = 9;
With -g --computed-gotos option this value specifies the com-
plexity threshold that triggers the generation of jump tables
rather than nested if statements and bit masks.
re2c:cond:divider = '/* *********************************** */';
Allows one to customize the divider for condition blocks. One
can use @@ to insert condition name.
re2c:cond:divider@cond = @@;
Specifies the placeholder that will be replaced with condition
name in re2c:cond:divider.
re2c:condenumprefix = yyc;
Specifies the prefix used for condition identifiers.
re2c:cond:goto@cond = @@;
Specifies the placeholder that will be replaced with condition
label in re2c:cond:goto.
re2c:cond:goto = 'goto @@;';
Allows one to customize goto statements used with :=> style
rules. One can use @@ to insert the condition name.
re2c:condprefix = yyc;
Specifies the prefix used for condition labels.
re2c:define:YYBACKUPCTX = 'YYBACKUPCTX';
Replaces YYBACKUPCTX identifier with the specified string.
re2c:define:YYBACKUP = 'YYBACKUP';
Replaces YYBACKUP identifier with the specified string.
re2c:define:YYCONDTYPE = 'YYCONDTYPE';
Enumeration type used for condition identifiers.
re2c:define:YYCTXMARKER = 'YYCTXMARKER';
Replaces the YYCTXMARKER placeholder with the specified identi-
fier.
re2c:define:YYCTYPE = 'YYCTYPE';
Replaces the YYCTYPE placeholder with the specified type.
re2c:define:YYCURSOR = 'YYCURSOR';
Replaces the YYCURSOR placeholder with the specified identifier.
re2c:define:YYDEBUG = 'YYDEBUG';
Replaces the YYDEBUG placeholder with the specified identifier.
re2c:define:YYFILL@len = '@@';
Any occurrence of this text inside of a YYFILL will be replaced
with the actual argument.
re2c:define:YYFILL:naked = 0;
Allows one to customize YYFILL invocation. If the value is
non-zero, re2c outputs the value of re2c:define:YYFILL configu-
ration (YYFILL by default) without any decoration: no parenthe-
ses and no semicolon (or comparison against zero in the case of
EOF rule). Otherwise the semicolon (or the comparison) is gen-
erated, and parentheses are controlled by the re2c:yyfill:param-
eter configuration.
re2c:define:YYFILL = 'YYFILL';
Define a substitution for YYFILL. By default re2c generates an
argument in parentheses and a semicolon after YYFILL. If you
need to make YYFILL an arbitrary statement rather than a call,
set re2c:define:YYFILL:naked to a non-zero value.
re2c:define:YYGETCONDITION:naked = 0;
Controls the parentheses after YYGETCONDITION. If non-zero, the
parentheses are omitted. If zero, they are generated.
re2c:define:YYGETCONDITION = 'YYGETCONDITION';
Substitution for YYGETCONDITION. By default re2c generates
parentheses after YYGETCONDITION. Set re2c:define:YYGETCONDI-
TION:naked to non-zero in order to omit the parentheses.
re2c:define:YYGETSTATE:naked = 0;
Controls the parentheses that follow YYGETSTATE. If non-zero,
the parentheses are omitted. If zero, they are generated.
re2c:define:YYGETSTATE = 'YYGETSTATE';
Substitution for YYGETSTATE. By default re2c generates paren-
theses after YYGETSTATE. Set re2c:define:YYGETSTATE:naked to
non-zero to omit the parentheses.
re2c:define:YYLESSTHAN = 'YYLESSTHAN';
Replaces YYLESSTHAN identifier with the specified string.
re2c:define:YYLIMIT = 'YYLIMIT';
Replaces the YYLIMIT placeholder with the specified identifier.
re2c:define:YYMARKER = 'YYMARKER';
Replaces the YYMARKER placeholder with the specified identifier.
re2c:define:YYMTAGN = 'YYMTAGN';
Replaces YYMTAGN identifier with the specified string.
re2c:define:YYMTAGP = 'YYMTAGP';
Replaces YYMTAGP identifier with the specified string.
re2c:define:YYMTAGPD = 'YYMTAGPD';
Replaces YYMTAGPD identifier with the specified string.
re2c:define:YYPEEK = 'YYPEEK';
Replaces YYPEEK identifier with the specified string.
re2c:define:YYRESTORECTX = 'YYRESTORECTX';
Replaces YYRESTORECTX identifier with the specified string.
re2c:define:YYRESTORE = 'YYRESTORE';
Replaces YYRESTORE identifier with the specified string.
re2c:define:YYRESTORETAG = 'YYRESTORETAG';
Replaces YYRESTORETAG identifier with the specified string.
re2c:define:YYSETCONDITION@cond = '@@';
Any occurrence of this text inside of YYSETCONDITION will be re-
placed with the actual argument.
re2c:define:YYSETCONDITION:naked = 0;
Controls the argument in parentheses and the semicolon after YY-
SETCONDITION. If non-zero, both the argument and the semicolon
are omitted. If zero, both the argument and the semicolon are
generated.
re2c:define:YYSETCONDITION = 'YYSETCONDITION';
Substitution for YYSETCONDITION. By default re2c generates an
argument in parentheses followed by semicolon after YYSETCONDI-
TION. If you need to make YYSETCONDITION an arbitrary statement
rather than a call, set re2c:define:YYSETCONDITION:naked to
non-zero.
re2c:define:YYSETSTATE:naked = 0;
Controls the argument in parentheses and the semicolon after YY-
SETSTATE. If non-zero, both argument and the semicolon are omit-
ted. If zero, both the argument and the semicolon are generated.
re2c:define:YYSETSTATE@state = '@@';
Any occurrence of this text inside of YYSETSTATE will be re-
placed with the actual argument.
re2c:define:YYSETSTATE = 'YYSETSTATE';
Substitution for YYSETSTATE. By default re2c generates an argu-
ment in parentheses followed by a semicolon after YYSETSTATE. If
you need to make YYSETSTATE an arbitrary statement rather than a
call, set re2c:define:YYSETSTATE:naked to non-zero.
re2c:define:YYSKIP = 'YYSKIP';
Replaces YYSKIP identifier with the specified string.
re2c:define:YYSTAGN = 'YYSTAGN';
Replaces YYSTAGN identifier with the specified string.
re2c:define:YYSTAGP = 'YYSTAGP';
Replaces YYSTAGP identifier with the specified string.
re2c:define:YYSTAGPD = 'YYSTAGPD';
Replaces YYSTAGPD identifier with the specified string.
re2c:eof = -1;
Specifies the sentinel symbol used with EOF rule $ to check for
the end of input in the generated lexer. Default value is -1
(EOF rule is not used). Other possible values include all valid
code units. Only decimal numbers are recognized.
re2c:sentinel = -1;
Specifies the sentinel symbol used with the sentinel method of
checking for the end of input in the generated lexer (the case
when when bounds checking is disabled with re2c:yyfill:enable =
0; and EOF rule $ is not used). This configuration does not af-
fect code generation. It is used by re2c to verify that the sen-
tinel symbol is not allowed in the middle of the rule, and thus
prevent possible reads past the end of buffer and crashes in the
generated lexer. Default value is -1: in this case re2c assumes
that the sentinel symbol is 0 (which is by far the most common
case). Other possible values include all valid code units. Only
decimal numbers are recognized.
re2c:flags:8 or re2c:flags:utf-8
Same as -8 --utf-8 command-line option.
re2c:flags:b or re2c:flags:bit-vectors
Same as -b --bit-vectors command-line option.
re2c:flags:case-insensitive = 0;
Same as --case-insensitive command-line option.
re2c:flags:case-inverted = 0;
Same as --case-inverted command-line option.
re2c:flags:d or re2c:flags:debug-output
Same as -d --debug-output command-line option.
re2c:flags:dfa-minimization = 'moore';
Same as --dfa-minimization command-line option.
re2c:flags:eager-skip = 0;
Same as --eager-skip command-line option.
re2c:flags:e or re2c:flags:ecb
Same as -e --ecb command-line option.
re2c:flags:empty-class = 'match-empty';
Same as --empty-class command-line option.
re2c:flags:encoding-policy = 'ignore';
Same as --encoding-policy command-line option.
re2c:flags:g or re2c:flags:computed-gotos
Same as -g --computed-gotos command-line option.
re2c:flags:i or re2c:flags:no-debug-info
Same as -i --no-debug-info command-line option.
re2c:flags:input = 'default';
Same as --input command-line option.
re2c:flags:lookahead = 1;
Same as inverted --no-lookahead command-line option.
re2c:flags:optimize-tags = 1;
Same as inverted --no-optimize-tags command-line option.
re2c:flags:P or re2c:flags:posix-captures
Same as -P --posix-captures command-line option.
re2c:flags:s or re2c:flags:nested-ifs
Same as -s --nested-ifs command-line option.
re2c:flags:T or re2c:flags:tags
Same as -T --tags command-line option.
re2c:flags:u or re2c:flags:unicode
Same as -u --unicode command-line option.
re2c:flags:w or re2c:flags:wide-chars
Same as -w --wide-chars command-line option.
re2c:flags:x or re2c:flags:utf-16
Same as -x --utf-16 command-line option.
re2c:indent:string = '\t';
Specifies the string to use for indentation. Requires a string
that contains only whitespace (unless you need something else
for external tools). The easiest way to specify spaces is to en-
close them in single or double quotes. If you do not want any
indentation at all, you can set this to ''.
re2c:indent:top = 0;
Specifies the minimum amount of indentation to use. Requires a
numeric value greater than or equal to zero.
re2c:labelprefix = 'yy';
Allows one to change the prefix of numbered labels. The default
is yy. Can be set any string that is valid in a label name.
re2c:label:yyFillLabel = 'yyFillLabel';
Overrides the name of the yyFillLabel label.
re2c:label:yyNext = 'yyNext';
Overrides the name of the yyNext label.
re2c:startlabel = 0;
If set to a non zero integer, then the start label of the next
scanner block will be generated even if it isn't used by the
scanner itself. Otherwise, the normal yy0-like start label is
only generated if needed. If set to a text value, then a label
with that text will be generated regardless of whether the nor-
mal start label is used or not. This setting is reset to 0 after
a start label has been generated.
re2c:state:abort = 0;
When not zero and the -f --storable-state switch is active, then
the YYGETSTATE block will contain a default case that aborts and
a -1 case will be used for initialization.
re2c:state:nextlabel = 0;
Used when -f --storable-state is active to control whether the
YYGETSTATE block is followed by a yyNext: label line. Instead
of using yyNext, you can usually also use configuration startla-
bel to force a specific start label or default to yy0 as a start
label. Instead of using a dedicated label, it is often better to
separate the YYGETSTATE code from the actual scanner code by
placing a /*!getstate:re2c*/ comment.
re2c:tags:expression = '@@';
Allows one to customize the way re2c addresses tag variables: by
default it emits expressions of the form yyt<N>, but this might
be inconvenient if tag variables are defined as fields in a
struct, or for any other reason require special accessors. For
example, setting re2c:tags:expression = p->@@ will result in
p->yyt<N>.
re2c:tags:prefix = 'yyt';
Allows one to override prefix of tag variables.
re2c:variable:yyaccept = yyaccept;
Overrides the name of the yyaccept variable.
re2c:variable:yybm = 'yybm';
Overrides the name of the yybm variable.
re2c:variable:yych = 'yych';
Overrides the name of the yych variable.
re2c:variable:yyctable = 'yyctable';
When both -c --conditions and -g --computed-gotos are active,
re2c will use this variable to generate a static jump table for
YYGETCONDITION.
re2c:variable:yystable = 'yystable';
Deprecated.
re2c:variable:yytarget = 'yytarget';
Overrides the name of the yytarget variable.
re2c:yybm:hex = 0;
If set to zero, a decimal table will be used. Otherwise, a hexa-
decimal table will be generated.
re2c:yych:conversion = 0;
When this setting is non zero, re2c automatically generates con-
version code whenever yych gets read. In this case, the type
must be defined using re2c:define:YYCTYPE.
re2c:yych:emit = 1;
Set this to zero to suppress the generation of yych.
re2c:yyfill:check = 1;
This can be set to 0 to suppress the generations of YYCURSOR and
YYLIMIT based precondition checks. This option is useful when
YYLIMIT + YYMAXFILL is always accessible.
re2c:yyfill:enable = 1;
Set this to zero to suppress the generation of YYFILL (n). When
using this, be sure to verify that the generated scanner does
not read beyond the available input, as allowing such behavior
might introduce severe security issues to your programs.
re2c:yyfill:parameter = 1;
Controls the argument in the parentheses that follow YYFILL. If
zero, the argument is omitted. If non-zero, the argument is
generated unless re2c:define:YYFILL:naked is set to non-zero.
EOF HANDLING
Re2c provides a number of ways to handle end-of-input situation. Which
way to use depends on the complexity of regular expressions, perfor-
mance considerations, the need for input buffering and various other
factors. EOF handling is probably the most complex part of re2c user
interface --- it definitely requires a bit of understanding of how the
generated lexer works. But in return is allows the user to customize
lexer for a particular environment and avoid the unnecessary overhead
of generic methods when a simpler method is sufficient. Roughly speak-
ing, there are four main methods:
o using sentinel symbol (simple and efficient, but limited)
o bounds checking with padding (generic, but complex)
o EOF rule: a combination of sentinel symbol and bounds checking
(generic and simple, can be more or less efficient than bounds check-
ing with padding depending on the grammar)
o using generic API (user-defined, so may be incorrect ;])
Using sentinel symbol
This is the simplest and the most efficient method. It is applicable in
cases when the input is small enough to fit into a continuous memory
buffer and there is a natural "sentinel" symbol --- a code unit that is
not allowed by any of the regular expressions in grammar (except possi-
bly as a terminating character). Sentinel symbol never appears in
well-formed input, therefore it can be appended at the end of input and
used as a stop signal by the lexer. A good example of such input is a
null-terminated C-string, provided that the grammar does not allow NULL
in the middle of lexemes. Sentinel method is very efficient, because
the lexer does not need to perform any additional checks for the end of
input --- it comes naturally as a part of processing the next charac-
ter. It is very important that the sentinel symbol is not allowed in
the middle of the rule --- otherwise on some inputs the lexer may read
past the end of buffer and crash or cause memory corruption. Re2c veri-
fies this automatically. Use re2c:sentinel configuration to specify
which sentinel symbol is used.
Below is an example of using sentinel method. Configuration re2c:yy-
fill:enable = 0; suppresses generation of end-of-input checks and YY-
FILL calls.
#include <assert.h>
static int lex(const char *YYCURSOR)
{
int count = 0;
loop:
/*!re2c
re2c:define:YYCTYPE = char;
re2c:yyfill:enable = 0;
* { return -1; }
[\x00] { return count; }
[a-z]+ { ++count; goto loop; }
[ ]+ { goto loop; }
*/
}
int main()
{
assert(lex("") == 0);
assert(lex("one two three") == 3);
assert(lex("one two 123?") == -1);
return 0;
}
Bounds checking with padding
Bounds checking is a generic method: it can be used with any input
grammar. The basic idea is simple: we need to check for the end of in-
put before reading the next input character. However, if implemented in
a straightforward way, this would be quite inefficient: checking on
each input character would cause a major slowdown. Re2c avoids slowdown
by generating checks only in certain key states of the lexer, and let-
ting it run without checks in-between the key states. More precisely,
re2c computes strongly connected components (SCCs) of the underlying
DFA (which roughly correspond to loops), and generates only a few
checks per each SCC (usually just one, but in general enough to make
the SCC acyclic). The check is of the form (YYLIMIT - YYCURSOR) < n,
where n is the maximal length of a simple path in the corresponding
SCC. If this condiiton is true, the lexer calls YYFILL(n), which must
either supply at least n input characters, or do not return. When the
lexer continues after the check, it is certain that the next n charac-
ters can be read safely without checks.
This approach reduces the number of checks significantly (and makes the
lexer much faster as a result), but it has a downside. Since the lexer
checks for multiple characters at once, it may end up in a situation
when there are a few remaining input characters (less than n) corre-
sponding to a short path in the SCC, but the lexer cannot proceed be-
cause of the check, and YYFILL cannot supply more character because it
is the end of input. To solve this problem, re2c requires that addi-
tional padding consisting of fake characters is appended at the end of
input. The length of padding should be YYMAXFILL, which equals to the
maximum n parameter to YYFILL and must be generated by re2c using
/*!max:re2c*/ directive. The fake characters should not form a valid
lexeme suffix, otherwise the lexer may be fooled into matching a fake
lexeme. Usually it's a good idea to use NULL characters for padding.
Below is an example of using bounds checking with padding. Note that
the grammar rule for single-quoted strings allows arbitrary symbols in
the middle of lexeme, so there is no natural sentinel in the grammar.
Strings like "aha\0ha" are perfectly valid, but ill-formed strings like
"aha\0 are also possible and shouldn't crash the lexer. In this example
we do not use buffer refilling, therefore YYFILL definition simply re-
turns an error. Note that YYFILL will only be called after the lexer
reaches padding, because only then will the check condition be satis-
fied.
#include <assert.h>
#include <stdlib.h>
#include <string.h>
/*!max:re2c*/
static int lex(const char *str)
{
const size_t len = strlen(str);
char *buf = malloc(len + YYMAXFILL);
memcpy(buf, str, len);
memset(buf + len, 0, YYMAXFILL);
const char *YYCURSOR = buf;
const char *YYLIMIT = buf + len + YYMAXFILL;
int count = 0;
loop:
/*!re2c
re2c:define:YYCTYPE = char;
re2c:define:YYFILL:naked = 1;
re2c:define:YYFILL = "goto error;";
* { goto error; }
[\x00] { if (YYCURSOR == YYLIMIT) goto end; else goto error; }
[a-z]+ { ++count; goto loop; }
['] ([^'] | [\\]['])* ['] { ++count; goto loop; }
[ ]+ { goto loop; }
*/
error:
count = -1;
end:
free(buf);
return count;
}
int main()
{
assert(lex("") == 0);
assert(lex("one two three") == 3);
assert(lex("one two 123?") == -1);
assert(lex("one 'two' 'th\\'ree' '123?' ''") == 5);
assert(lex("one 'two' 'three") == -1);
return 0;
}
EOF rule
EOF rule $ was introduced in version 1.2. It is a hybrid approach that
tries to take the best of both worlds: simplicity and efficiency of the
sentinel method combined with the generality of bounds-checking method.
The idea is to appoint an arbitrary symbol to be the sentinel, and only
perform further bounds checking if the sentinel symbol matches (more
precisely, if the symbol class that contains it matches). The check is
of the form YYLIMIT <= YYCURSOR. If this condition is not satisfied,
then the sentinel is just an ordinary input character and the lexer
continues. Otherwise this is a real sentinel, and the lexer calls YY-
FILL(). If YYFILL returns zero, the lexer assumes that it has more in-
put and tries to re-match. Otherwise YYFILL returns non-zero and the
lexer knows that it has reached the end of input. At this point there
are three possibilities. First, it might have already matched a shorter
lexeme --- in this case it just rolls back to the last accepting state.
Second, it might have consumed some characters, but failed to match ---
in this case it falls back to default rule *. Finally, it might be in
the initial state --- in this (and only this!) case it matches EOF rule
$.
Below is an example of using EOF rule. Configuration re2c:yyfill:enable
= 0; suppresses generation of YYFILL calls (but not the bounds checks).
#include <assert.h>
#include <string.h>
static int lex(const char *str)
{
const char *YYCURSOR = str;
const char *YYLIMIT = str + strlen(str);
int count = 0;
loop:
/*!re2c
re2c:define:YYCTYPE = char;
re2c:yyfill:enable = 0;
re2c:eof = 0;
* { return -1; }
$ { return count; }
[a-z]+ { ++count; goto loop; }
['] ([^'] | [\\]['])* ['] { ++count; goto loop; }
[ ]+ { goto loop; }
*/
}
int main()
{
assert(lex("") == 0);
assert(lex("one two three") == 3);
assert(lex("one two 123?") == -1);
assert(lex("one 'two' 'th\\'ree' '123?' ''") == 5);
assert(lex("one 'two' 'three") == -1);
return 0;
}
Using generic API
Generic API can be used with any of the above methods. It also allows
one to use a user-defined method by placing EOF checks in one of the
basic primitives. Usually this is either YYSKIP (the check is per-
formed when advancing to the next input character), or YYPEEK (the
check is performed when reading the next input character). The result-
ing methods are inefficient, as they check on each input character.
However, they can be useful in cases when the input cannot be buffered
or padded and does not contain a sentinel character at the end. One
should be cautious when using such ad-hoc methods, as it is easy to
overlook some corner cases and come up with a method that only par-
tially works. Also it should be noted that not everything can be ex-
pressed via generic API: for example, it is impossible to reimplement
the way EOF rule works (in particular, it is impossible to re-match the
character after successful YYFILL).
Below is an example of using YYSKIP to perform bounds checking without
padding. YYFILL generation is suppressed using re2c:yyfill:enable = 0;
configuration. Note that if the grammar was more complex, this method
might not work in case when two rules overlap and EOF check fails after
a shorter lexeme has already been matched (as it happens in our exam-
ple, there are no overlapping rules).
#include <assert.h>
#include <string.h>
#define YYPEEK() *cur
#define YYSKIP() if (++cur > lim) return -1
static int lex(const char *str)
{
const char *cur = str;
const char *lim = str + strlen(str) + 1;
int count = 0;
loop:
/*!re2c
re2c:define:YYCTYPE = char;
re2c:yyfill:enable = 0;
re2c:flags:input = custom;
* { return -1; }
[\x00] { return cur == lim ? count : -1; }
[a-z]+ { ++count; goto loop; }
['] ([^'] | [\\]['])* ['] { ++count; goto loop; }
[ ]+ { goto loop; }
*/
}
int main()
{
assert(lex("") == 0);
assert(lex("one two three") == 3);
assert(lex("one two 123?") == -1);
assert(lex("one 'two' 'th\\'ree' '123?' ''") == 5);
assert(lex("one 'two' 'three") == -1);
return 0;
}
BUFFER REFILLING
The need for buffering arises when the input cannot be mapped in memory
all at once: either it is too large, or it comes in a streaming fashion
(like reading from a socket). The usual technique in such cases is to
allocate a fixed-sized memory buffer and process input in chunks that
fit into the buffer. When the current chunk is processed, it is moved
out and new data is moved in. In practice it is somewhat more complex,
because lexer state consists not of a single input position, but a set
of interrelated posiitons:
o cursor: the next input character to be read (YYCURSOR in default API
or YYSKIP/YYPEEK in generic API)
o limit: the position after the last available input character (YYLIMIT
in default API, implicitly handled by YYLESSTHAN in generic API)
o marker: the position of the most recent match, if any (YYMARKER in
default API or YYBACKUP/YYRESTORE in generic API)
o token: the start of the current lexeme (implicit in re2c API, as it
is not needed for the normal lexer operation and can be defined and
updated by the user)
o context marker: the position of the trailing context (YYCTXMARKER in
default API or YYBACKUPCTX/YYRESTORECTX in generic API)
o tag variables: submatch positions (defined with /*!stags:re2c*/ and
/*!mtags:re2c*/ directives and YYSTAGP/YYSTAGN/YYMTAGP/YYMTAGN in
generic API)
Not all these are used in every case, but if used, they must be updated
by YYFILL. All active positions are contained in the segment between
token and cursor, therefore everything between buffer start and token
can be discarded, the segment from token and up to limit should be
moved to the beginning of buffer, and the free space at the end of buf-
fer should be filled with new data. In order to avoid frequent YYFILL
calls it is best to fill in as many input characters as possible (even
though fewer characters might suffice to resume the lexer). The details
of YYFILL implementation are slightly different depending on which EOF
handling method is used: the case of EOF rule is somewhat simpler than
the case of bounds-checking with padding. Also note that if -f
--storable-state option is used, YYFILL has slightly different seman-
tics (desrbed in the section about storable state).
YYFILL with EOF rule
If EOF rule is used, YYFILL is a function-like primitive that accepts
no arguments and returns a value which is checked against zero. YYFILL
invocation is triggered by condition YYLIMIT <= YYCURSOR in default API
and YYLESSTHAN() in generic API. A non-zero return value means that YY-
FILL has failed. A successful YYFILL call must supply at least one
character and adjust input positions accordingly. Limit must always be
set to one after the last input position in buffer, and the character
at the limit position must be the sentinel symbol specified by re2c:eof
configuration. The pictures below show the relative locations of input
positions in buffer before and after YYFILL call (sentinel symbol is
marked with #, and the second picture shows the case when there is not
enough input to fill the whole buffer).
<-- shift -->
>-A------------B---------C-------------D#-----------E->
buffer token marker limit,
cursor
>-A------------B---------C-------------D------------E#->
buffer, marker cursor limit
token
<-- shift -->
>-A------------B---------C-------------D#--E (EOF)
buffer token marker limit,
cursor
>-A------------B---------C-------------D---E#........
buffer, marker cursor limit
token
Here is an example of a program that reads input file input.txt in
chunks of 4096 bytes and uses EOF rule.
#include <stdio.h>
#include <string.h>
#define SIZE 4096
typedef struct {
FILE *file;
char buf[SIZE + 1], *lim, *cur, *tok;
int eof;
} Input;
static int fill(Input *in)
{
if (in->eof) {
return 1;
}
const size_t free = in->tok - in->buf;
if (free < 1) {
return 2;
}
memmove(in->buf, in->tok, in->lim - in->tok);
in->lim -= free;
in->cur -= free;
in->tok -= free;
in->lim += fread(in->lim, 1, free, in->file);
in->lim[0] = 0;
in->eof |= in->lim < in->buf + SIZE;
return 0;
}
static void init(Input *in, FILE *file)
{
in->file = file;
in->cur = in->tok = in->lim = in->buf + SIZE;
in->eof = 0;
fill(in);
}
#define YYFILL() fill(in)
static int lex(Input *in)
{
int count = 0;
loop:
in->tok = in->cur;
/*!re2c
re2c:define:YYCTYPE = char;
re2c:define:YYCURSOR = in->cur;
re2c:define:YYLIMIT = in->lim;
re2c:eof = 0;
* { return -1; }
$ { return count; }
[a-z]+ { ++count; goto loop; }
['] ([^'] | [\\]['])* ['] { ++count; goto loop; }
[ ]+ { goto loop; }
*/
}
int main()
{
FILE *f = fopen("input.txt", "rb");
if (!f) return 1;
Input in;
init(&in, f);
printf("count: %d\n", lex(&in));
fclose(f);
return 0;
}
YYFILL with padding
In the default case (when EOF rule is not used) YYFILL is a func-
tion-like primitive that accepts a single argument and does not return
any value. YYFILL invocation is triggered by condition (YYLIMIT - YY-
CURSOR) < n in default API and YYLESSTHAN(n) in generic API. The argu-
ment passed to YYFILL is the minimal number of characters that must be
supplied. If it fails to do so, YYFILL must not return to the lexer
(for that reason it is best implemented as a macro that returns from
the calling function on failure). In case of a successful YYFILL invo-
cation the limit position must be set either to one after the last in-
put position in buffer, or to the end of YYMAXFILL padding (in case YY-
FILL has successfully read at least n characters, but not enough to
fill the entire buffer). The pictures below show the relative locations
of input positions in buffer before and after YYFILL invocation (YYMAX-
FILL padding on the second picture is marked with # symbols).
<-- shift --> <-- need -->
>-A------------B---------C-----D-------E---F--------G->
buffer token marker cursor limit
>-A------------B---------C-----D-------E---F--------G->
buffer, marker cursor limit
token
<-- shift --> <-- need -->
>-A------------B---------C-----D-------E-F (EOF)
buffer token marker cursor limit
>-A------------B---------C-----D-------E-F###############
buffer, marker cursor limit
token <- YYMAXFILL ->
Here is an example of a program that reads input file input.txt in
chunks of 4096 bytes and uses bounds-checking with padding.
#include <stdio.h>
#include <string.h>
/*!max:re2c*/
#define SIZE 4096
typedef struct {
FILE *file;
char buf[SIZE + YYMAXFILL], *lim, *cur, *tok;
int eof;
} Input;
static int fill(Input *in, size_t need)
{
if (in->eof) {
return 1;
}
const size_t free = in->tok - in->buf;
if (free < need) {
return 2;
}
memmove(in->buf, in->tok, in->lim - in->tok);
in->lim -= free;
in->cur -= free;
in->tok -= free;
in->lim += fread(in->lim, 1, free, in->file);
if (in->lim < in->buf + SIZE) {
in->eof = 1;
memset(in->lim, 0, YYMAXFILL);
in->lim += YYMAXFILL;
}
return 0;
}
static void init(Input *in, FILE *file)
{
in->file = file;
in->cur = in->tok = in->lim = in->buf + SIZE;
in->eof = 0;
fill(in, 1);
}
#define YYFILL(n) if (fill(in, n) != 0) return -1
static int lex(Input *in)
{
int count = 0;
loop:
in->tok = in->cur;
/*!re2c
re2c:define:YYCTYPE = char;
re2c:define:YYCURSOR = in->cur;
re2c:define:YYLIMIT = in->lim;
* { return -1; }
[\x00] { return (YYMAXFILL == in->lim - in->tok) ? count : -1; }
[a-z]+ { ++count; goto loop; }
['] ([^'] | [\\]['])* ['] { ++count; goto loop; }
[ ]+ { goto loop; }
*/
}
int main()
{
FILE *f = fopen("input.txt", "rb");
if (!f) return 1;
Input in;
init(&in, f);
printf("count: %d\n", lex(&in));
fclose(f);
return 0;
}
INCLUDE FILES
Re2c allows one to include other files using directive /*!include:re2c
FILE */, where FILE is the name of file to be included. Re2c looks for
included files in the directory of the including file and in include
locations, which can be specified with -I option. Re2c include direc-
tive works in the same way as C/C++ #include: the contents of FILE are
copy-pasted verbatim in place of the directive. Include files may have
further includes of their own. Re2c provides some predefined include
files that can be found in the include/ subdirectory of the project.
These files contain definitions that can be useful to other projects
(such as Unicode categories) and form something like a standard library
for re2c.
Here is an example of using include files:
// definitions.re
/*!re2c
alpha = [a-zA-Z];
digit = [0-9];
*/
// main.re
/*!include:re2c "definitions.re" */
int lex(const char *YYCURSOR)
{
const char *YYMARKER;
/*!re2c
alpha { return 1; }
digit { return 2; }
* { return 0; }
*/
}
HEADER FILES
Re2c allows one to generate header file from the input .re file using
option -t --type-header (or the corresponding configurations) and di-
rectives /*!header:re2c:on*/ and /*!header:re2c:off*/. The first direc-
tive marks the beginning of header file, and the second directive marks
the end of it. Everything between these directives is processed by
re2c, and the generated code is written to the file specified by the -t
--type-header option (or stdout if this option was not used). Autogen-
erated header file may be needed in cases when re2c is used to generate
definitions of constants, variables and structs that must be visible
from other translation units.
Here is an example of generating a header that contains definitions of
YYMAXFILL and lexer state with tag variables. Note that YYMAXFILL and
tag variables depend on the grammar in the .re file and cannot be
hard-coded.
/*!header:re2c:on*/
/*!max:re2c*/
struct State {
char buffer[4096 + YYMAXFILL], *cursor, *marker, *limit;
/*!stags:re2c format = "char *@@; "; */
};
/*!header:re2c:off*/
#include "lex.h"
#define YYCTYPE char
#define YYCURSOR state->cursor
#define YYMARKER state->marker
#define YYLIMIT state->limit
#define YYFILL(n) return 2
int lex(State *state)
{
char *x, *y;
/*!re2c
re2c:tags:expression = state->@@;
re2c:flags:t = lex.h;
"a"* @x "b"* @y "c"* { return 0; }
* { return 1; }
*/
}
The generated header looks like this:
#define YYMAXFILL 1
struct State {
char buffer[4096 + YYMAXFILL], *cursor, *marker, *limit;
char *yyt1; char *yyt2;
};
SUBMATCH EXTRACTION
Re2c has two options for submatch extraction.
The first option is -T --tags. With this option one can use standalone
tags of the form @stag and #mtag, where stag and mtag are arbitrary
used-defined names. Tags can be used anywhere inside of a regular ex-
pression; semantically they are just position markers. Tags of the form
@stag are called s-tags: they denote a single submatch value (the last
input position where this tag matched). Tags of the form #mtag are
called m-tags: they denote multiple submatch values (the whole history
of repetitions of this tag). All tags should be defined by the user as
variables with the corresponding names. With standalone tags re2c uses
leftmost greedy disambiguation: submatch positions correspond to the
leftmost matching path through the regular expression.
The second option is -P --posix-captures: it enables POSIX-compliant
capturing groups. In this mode parentheses in regular expressions de-
note the beginning and the end of capturing groups; the whole regular
expression is group number zero. The number of groups for the matching
rule is stored in a variable yynmatch, and submatch results are stored
in yypmatch array. Both yynmatch and yypmatch should be defined by the
user, and yypmatch size must be at least [yynmatch * 2]. Re2c provides
a directive /*!maxnmatch:re2c*/ that defines YYMAXNMATCH: a constant
equal to the maximal value of yynmatch among all rules. Note that re2c
implements POSIX-compliant disambiguation: each subexpression matches
as long as possible, and subexpressions that start earlier in regular
expression have priority over those starting later. Capturing groups
are translated into s-tags under the hood, therefore we use the word
"tag" to describe them as well.
With both -P --posix-captures and T --tags options re2c uses efficient
submatch extraction algorithm described in the Tagged Deterministic Fi-
nite Automata with Lookahead paper. The overhead on submatch extraction
in the generated lexer grows with the number of tags --- if this number
is moderate, the overhead is barely noticeable. In the lexer tags are
implemented using a number of tag variables generated by re2c. There is
no one-to-one correspondence between tag variables and tags: a single
variable may be reused for different tags, and one tag may require mul-
tiple variables to hold all its ambiguous values. Eventually ambiguity
is resolved, and only one final variable per tag survives. When a rule
matches, all its tags are set to the values of the corresponding tag
variables. The exact number of tag variables is unknown to the user;
this number is determined by re2c. However, tag variables should be de-
fined by the user as a part of the lexer state and updated by YYFILL,
therefore re2c provides directives /*!stags:re2c*/ and /*!mtags:re2c*/
that can be used to declare, initialize and manipulate tag variables.
These directives have two optional configurations: format = "@@";
(specifies the template where @@ is substituted with the name of each
tag variable), and separator = ""; (specifies the piece of code used to
join the generated pieces for different tag variables).
S-tags support the following operations:
o save input position to an s-tag: t = YYCURSOR with default API or a
user-defined operation YYSTAGP(t) with generic API
o save default value to an s-tag: t = NULL with default API or a
user-defined operation YYSTAGN(t) with generic API
o copy one s-tag to another: t1 = t2
M-tags support the following operations:
o append input position to an m-tag: a user-defined operation YYM-
TAGP(t) with both default and generic API
o append default value to an m-tag: a user-defined operation YYMTAGN(t)
with both default and generic API
o copy one m-tag to another: t1 = t2
S-tags can be implemented as scalar values (pointers or offsets).
M-tags need a more complex representation, as they need to store a se-
quence of tag values. The most naive and inefficient representation of
an m-tag is a list (array, vector) of tag values; a more efficient rep-
resentation is to store all m-tags in a prefix-tree represented as ar-
ray of nodes (v, p), where v is tag value and p is a pointer to parent
node.
Here is an example of using s-tags to parse an IPv4 address.
#include <assert.h>
#include <stdint.h>
static uint32_t num(const char *s, const char *e)
{
uint32_t n = 0;
for (; s < e; ++s) n = n * 10 + (*s - '0');
return n;
}
static uint32_t lex(const char *YYCURSOR)
{
const char *YYMARKER, *o1, *o2, *o3, *o4;
/*!stags:re2c format = 'const char *@@;'; */
/*!re2c
re2c:define:YYCTYPE = char;
re2c:yyfill:enable = 0;
re2c:flags:tags = 1;
oct = [0-9]{1,3};
dot = [.];
@o1 oct dot @o2 oct dot @o3 oct dot @o4 oct {
return num(o4, YYCURSOR)
+ (num(o3, o4 - 1) << 8)
+ (num(o2, o3 - 1) << 16)
+ (num(o1, o2 - 1) << 24);
}
* { return 0; }
*/
}
int main()
{
assert(lex("1.2.3.4") == 0x01020304);
assert(lex("127.0.0.1") == 0x7f000001);
assert(lex("255.255.255.255") == 0xffffffff);
return 0;
}
Here is an example of using POSIX capturing groups to parse an IPv4 ad-
dress.
#include <assert.h>
#include <stdint.h>
static uint32_t num(const char *s, const char *e)
{
uint32_t n = 0;
for (; s < e; ++s) n = n * 10 + (*s - '0');
return n;
}
/*!maxnmatch:re2c*/
static uint32_t lex(const char *YYCURSOR)
{
const char *YYMARKER;
const char *yypmatch[YYMAXNMATCH];
uint32_t yynmatch;
/*!stags:re2c format = 'const char *@@;'; */
/*!re2c
re2c:define:YYCTYPE = char;
re2c:yyfill:enable = 0;
re2c:flags:posix-captures = 1;
oct = [0-9]{1,3};
dot = [.];
(oct) dot (oct) dot (oct) dot (oct) {
return num(yypmatch[8], yypmatch[9])
+ (num(yypmatch[6], yypmatch[7]) << 8)
+ (num(yypmatch[4], yypmatch[5]) << 16)
+ (num(yypmatch[2], yypmatch[3]) << 24);
}
* { return 0; }
*/
}
int main()
{
assert(lex("1.2.3.4") == 0x01020304);
assert(lex("127.0.0.1") == 0x7f000001);
assert(lex("255.255.255.255") == 0xffffffff);
return 0;
}
Here is an example of using m-tags to parse a semicolon-separated se-
quence of words (C++). Tag variables are stored in a tree that is
packed in a vector.
#include <assert.h>
#include <vector>
#include <string>
static const int ROOT = -1;
struct Mtag {
int pred;
const char *tag;
};
typedef std::vector<Mtag> MtagTree;
typedef std::vector<std::string> Words;
static void mtag(int *pt, const char *t, MtagTree *tree)
{
Mtag m = {*pt, t};
*pt = (int)tree->size();
tree->push_back(m);
}
static void unfold(const MtagTree &tree, int x, int y, Words &words)
{
if (x == ROOT) return;
unfold(tree, tree[x].pred, tree[y].pred, words);
const char *px = tree[x].tag, *py = tree[y].tag;
words.push_back(std::string(px, py - px));
}
#define YYMTAGP(t) mtag(&t, YYCURSOR, &tree)
#define YYMTAGN(t) mtag(&t, NULL, &tree)
static bool lex(const char *YYCURSOR, Words &words)
{
const char *YYMARKER;
/*!mtags:re2c format = "int @@ = ROOT;"; */
MtagTree tree;
int x, y;
/*!re2c
re2c:define:YYCTYPE = char;
re2c:yyfill:enable = 0;
re2c:flags:tags = 1;
(#x [a-zA-Z0-9_]+ #y [;])+ {
words.clear();
unfold(tree, x, y, words);
return true;
}
* { return false; }
*/
}
int main()
{
Words w;
assert(lex("one;tw0;three;", w) && w == Words({"one", "tw0", "three"}));
return 0;
}
STORABLE STATE
With -f --storable-state option re2c generates a lexer that can store
its current state, return to the caller, and later resume operations
exactly where it left off. The default mode of operation in re2c is a
"pull" model, in which the lexer "pulls" more input whenever it needs
it. This may be unacceptable in cases when the input becomes available
piece by piece (for example, if the lexer is invoked by the parser, or
if the lexer program communicates via a socket protocol with some other
program that must wait for a reply from the lexer before it transmits
the next message). Storable state feature is intended exactly for such
cases: it allows one to generate lexers that work in a "push" model.
When the lexer needs more input, it stores its state and returns to the
caller. Later, when more input becomes available, the caller resumes
the lexer exactly where it stopped. There are a few changes necessary
compared to the "pull" model:
o Define YYSETSTATE() and YYGETSTATE(state) promitives.
o Define yych, yyaccept and state variables as a part of persistent
lexer state. The state variable should be initialized to -1.
o YYFILL should return to the outer program instead of trying to supply
more input. Return code should indicate that lexer needs more input.
o The outer program should recognize situations when lexer needs more
input and respond appropriately.
o Use /*!getstate:re2c*/ directive if it is necessary to execute any
code before entering the lexer.
o Use configurations state:abort and state:nextlabel to further tweak
the generated code.
Here is an example of a "push"-model lexer that reads input from stdin
and expects a sequence of words separated by spaces and newlines. The
lexer loops forever, waiting for more input. It can be terminated by
sending a special EOF token --- a word "stop", in which case the lexer
terminates successfully and prints the number of words it has seen. Ab-
normal termination happens in case of a syntax error, premature end of
input (without the "stop" word) or in case the buffer is too small to
hold a lexeme (for example, if one of the words exceeds buffer size).
Premature end of input happens in case the lexer fails to read any in-
put while being in the initial state --- this is the only case when EOF
rule matches. Note that the lexer may call YYFILL twice before termi-
nating (and thus require hitting Ctrl+D a few times). First time YYFILL
is called when the lexer expects continuation of the current greedy
lexeme (either a word or a whitespace sequence). If YYFILL fails, the
lexer knows that it has reached the end of the current lexeme and exe-
cutes the corresponding semantic action. The action jumps to the begin-
ning of the loop, the lexer enters the initial state and calls YYFILL
once more. If it fails, the lexer matches EOF rule. (Alternatively EOF
rule can be used for termination instead of a special EOF lexeme.)
#include <assert.h>
#include <stdio.h>
#include <string.h>
#define SIZE 4096
typedef struct {
char buf[SIZE + 1], *lim, *cur, *tok, yych;
unsigned yyaccept;
int state;
} Input;
static void init(Input *in)
{
in->cur = in->tok = in->lim = in->buf + SIZE;
in->lim[0] = 0; // append sentinel symbol
in->yych = 0;
in->yyaccept = 0;
in->state = -1;
}
static int fill(Input *in)
{
const size_t shift = in->tok - in->buf;
const size_t free = SIZE - (in->lim - in->tok);
if (free < 1) return 1; // not enough space in buffer
memmove(in->buf, in->tok, SIZE - shift);
in->lim -= shift;
in->cur -= shift;
in->tok -= shift;
const size_t read = fread(in->lim, 1, free, stdin);
in->lim += read;
in->lim[0] = 0; // append sentinel symbol
return 0;
}
typedef enum {OK, SYNTAX_ERROR, UNEXPECTED_EOF, NEED_MORE_INPUT} Status;
#define YYGETSTATE() in->state
#define YYSETSTATE(s) in->state = s
#define YYFILL() return NEED_MORE_INPUT
static Status lex(Input *in, unsigned *words)
{
/*!getstate:re2c*/
loop:
in->tok = in->cur;
/*!re2c
re2c:define:YYCTYPE = char;
re2c:define:YYCURSOR = in->cur;
re2c:define:YYLIMIT = in->lim;
re2c:variable:yych = in->yych;
re2c:eof = 0;
* { return SYNTAX_ERROR; }
$ { return UNEXPECTED_EOF; }
"stop" { return OK; }
[\n ]+ { goto loop; }
[a-zA-Z]+ { *words = *words + 1; goto loop; }
*/
}
int main()
{
unsigned words = 0;
Input in;
init(&in);
for (;;) {
const Status st = lex(&in, &words);
if (st == OK) {
printf("word count: %u\n", words);
break;
}
else if (st == SYNTAX_ERROR) {
printf("error: unexpected symbol\n");
return 1;
}
else if (st == UNEXPECTED_EOF) {
printf("error: unexpected end of input\n");
return 2;
}
else if (fill(&in) != 0) {
printf("error: not enough space in buffer\n");
return 3;
}
}
return 0;
}
REUSABLE BLOCKS
Reuse mode is enabled with the -r --reusable option. In this mode re2c
allows one to reuse definitions, configurations and rules specified by
a /*!rules:re2c*/ block in subsequent /*!use:re2c*/ blocks. As of
re2c-1.2 it is possible to mix such blocks with normal /*!re2c*/
blocks; prior to that re2c expects a single rules-block followed by
use-blocks (normal blocks are disallowed). Use-blocks can have addi-
tional definitions, configurations and rules: they are merged to those
specified by the rules-block. A very common use case for -r --reusable
option is a lexer that supports multiple input encodings: lexer rules
are defined once and reused multiple times with encoding-specific con-
figurations, such as re2c:flags:utf-8.
Below is an example of a multi-encoding lexer: it reads a phrase with
Unicode math symbols and accepts input either in UTF8 or in UT32. Note
that the --input-encoding utf8 option allows us to write UTF8-encoded
symbols in the regular expressions; without this option re2c would
parse them as a plain ASCII byte sequnce (and we would have to use
hexadecimal escape sequences).
#include <assert.h>
#include <stdint.h>
/*!rules:re2c
re2c:yyfill:enable = 0;
"<for all>x <there exists>y: p(x, y)" { return 0; }
* { return 1; }
*/
static int lex_utf8(const uint8_t *YYCURSOR)
{
const uint8_t *YYMARKER;
/*!use:re2c
re2c:define:YYCTYPE = uint8_t;
re2c:flags:8 = 1;
*/
}
static int lex_utf32(const uint32_t *YYCURSOR)
{
const uint32_t *YYMARKER;
/*!use:re2c
re2c:define:YYCTYPE = uint32_t;
re2c:flags:8 = 0;
re2c:flags:u = 1;
*/
}
int main()
{
static const uint8_t s8[] = // UTF-8
{ 0xe2, 0x88, 0x80, 0x78, 0x20, 0xe2, 0x88, 0x83, 0x79
, 0x3a, 0x20, 0x70, 0x28, 0x78, 0x2c, 0x20, 0x79, 0x29 };
static const uint32_t s32[] = // UTF32
{ 0x00002200, 0x00000078, 0x00000020, 0x00002203
, 0x00000079, 0x0000003a, 0x00000020, 0x00000070
, 0x00000028, 0x00000078, 0x0000002c, 0x00000020
, 0x00000079, 0x00000029 };
assert(lex_utf8(s8) == 0);
assert(lex_utf32(s32) == 0);
return 0;
}
ENCODING SUPPORT
re2c supports the following encodings: ASCII (default), EBCDIC (-e),
UCS-2 (-w), UTF-16 (-x), UTF-32 (-u) and UTF-8 (-8). See also inplace
configuration re2c:flags.
The following concepts should be clarified when talking about encod-
ings. A code point is an abstract number that represents a single sym-
bol. A code unit is the smallest unit of memory, which is used in the
encoded text (it corresponds to one character in the input stream). One
or more code units may be needed to represent a single code point, de-
pending on the encoding. In a fixed-length encoding, each code point is
represented with an equal number of code units. In variable-length en-
codings, different code points can be represented with different number
of code units.
o ASCII is a fixed-length encoding. Its code space includes 0x100 code
points, from 0 to 0xFF. A code point is represented with exactly one
1-byte code unit, which has the same value as the code point. The
size of YYCTYPE must be 1 byte.
o EBCDIC is a fixed-length encoding. Its code space includes 0x100 code
points, from 0 to 0xFF. A code point is represented with exactly one
1-byte code unit, which has the same value as the code point. The
size of YYCTYPE must be 1 byte.
o UCS-2 is a fixed-length encoding. Its code space includes 0x10000
code points, from 0 to 0xFFFF. One code point is represented with ex-
actly one 2-byte code unit, which has the same value as the code
point. The size of YYCTYPE must be 2 bytes.
o UTF-16 is a variable-length encoding. Its code space includes all
Unicode code points, from 0 to 0xD7FF and from 0xE000 to 0x10FFFF.
One code point is represented with one or two 2-byte code units. The
size of YYCTYPE must be 2 bytes.
o UTF-32 is a fixed-length encoding. Its code space includes all Uni-
code code points, from 0 to 0xD7FF and from 0xE000 to 0x10FFFF. One
code point is represented with exactly one 4-byte code unit. The size
of YYCTYPE must be 4 bytes.
o UTF-8 is a variable-length encoding. Its code space includes all Uni-
code code points, from 0 to 0xD7FF and from 0xE000 to 0x10FFFF. One
code point is represented with a sequence of one, two, three, or four
1-byte code units. The size of YYCTYPE must be 1 byte.
In Unicode, values from range 0xD800 to 0xDFFF (surrogates) are not
valid Unicode code points. Any encoded sequence of code units that
would map to Unicode code points in the range 0xD800-0xDFFF, is
ill-formed. The user can control how re2c treats such ill-formed se-
quences with the --encoding-policy <policy> switch.
For some encodings, there are code units that never occur in a valid
encoded stream (e.g., 0xFF byte in UTF-8). If the generated scanner
must check for invalid input, the only correct way to do so is to use
the default rule (*). Note that the full range rule ([^]) won't catch
invalid code units when a variable-length encoding is used ([^] means
"any valid code point", whereas the default rule (*) means "any possi-
ble code unit").
START CONDITIONS
Conditions are enabled with -c --conditions. This option allows one to
encode multiple interrelated lexers within the same re2c block.
Each lexer corresponds to a single condition. It starts with a label
of the form yyc_name, where name is condition name and yyc prefix can
be adjusted with configuration re2c:condprefix. Different lexers are
separated with a comment /* *********************************** */
which can be adjusted with configuration re2c:cond:divider.
Furthermore, each condition has a unique identifier of the form yyc-
name, where name is condition name and yyc prefix can be adjusted with
configuration re2c:condenumprefix. Identifiers have the type YYCOND-
TYPE and should be generated with /*!types:re2c*/ directive or -t
--type-header option. Users shouldn't define these identifiers manu-
ally, as the order of conditions is not specified.
Before all conditions re2c generates entry code that checks the current
condition identifier and transfers control flow to the start label of
the active condition. After matching some rule of this condition,
lexer may either transfer control flow back to the entry code (after
executing the associated action and optionally setting another condi-
tion with =>), or use :=> shortcut and transition directly to the start
label of another condition (skipping the action and the entry code).
Configuration re2c:cond:goto allows one to change the default behavior.
Syntactically each rule must be preceded with a list of comma-separated
condition names or a wildcard * enclosed in angle brackets < and >.
Wildcard means "any condition" and is semantically equivalent to list-
ing all condition names. Here regexp is a regular expression, default
refers to the default rule *, and action is a block of C/C++ code.
o <conditions-or-wildcard> regexp-or-default action
o <conditions-or-wildcard> regexp-or-default => condition action
o <conditions-or-wildcard> regexp-or-default :=> condition
Rules with an exclamation mark ! in front of condition list have a spe-
cial meaning: they have no regular expression, and the associated ac-
tion is merged as an entry code to actions of normal rules. This might
be a convenient place to peform a routine task that is common to all
rules.
o <!conditions-or-wildcard> action
Another special form of rules with an empty condition list <> and no
regular expression allows one to specify an "entry condition" that can
be used to execute code before entering the lexer. It is semantically
equivalent to a condition with number zero, name 0 and an empty regular
expression.
o <> action
o <> => condition action
o <> :=> condition
SKELETON PROGRAMS
With the -S, --skeleton option, re2c ignores all non-re2c code and gen-
erates a self-contained C program that can be further compiled and exe-
cuted. The program consists of lexer code and input data. For each con-
structed DFA (block or condition) re2c generates a standalone lexer and
two files: an .input file with strings derived from the DFA and a .keys
file with expected match results. The program runs each lexer on the
corresponding .input file and compares results with the expectations.
Skeleton programs are very useful for a number of reasons:
o They can check correctness of various re2c optimizations (the data is
generated early in the process, before any DFA transformations have
taken place).
o Generating a set of input data with good coverage may be useful for
both testing and benchmarking.
o Generating self-contained executable programs allows one to get mini-
mized test cases (the original code may be large or have a lot of de-
pendencies).
The difficulty with generating input data is that for all but the most
trivial cases the number of possible input strings is too large (even
if the string length is limited). Re2c solves this difficulty by gener-
ating sufficiently many strings to cover almost all DFA transitions. It
uses the following algorithm. First, it constructs a skeleton of the
DFA. For encodings with 1-byte code unit size (such as ASCII, UTF-8 and
EBCDIC) skeleton is just an exact copy of the original DFA. For encod-
ings with multibyte code units skeleton is a copy of DFA with certain
transitions omitted: namely, re2c takes at most 256 code units for each
disjoint continuous range that corresponds to a DFA transition. The
chosen values are evenly distributed and include range bounds. Instead
of trying to cover all possible paths in the skeleton (which is infea-
sible) re2c generates sufficiently many paths to cover all skeleton
transitions, and thus trigger the corresponding conditional jumps in
the lexer. The algorithm implementation is limited by ~1Gb of transi-
tions and consumes constant amount of memory (re2c writes data to file
as soon as it is generated).
VISUALIZATION AND DEBUG
With the -D, --emit-dot option, re2c does not generate C/C++ code. In-
stead, it dumps the generated DFA in the DOT format. One can convert
this dump to an image of the DFA using graphviz or another library.
Note that this option shows the final DFA after it has gone through a
number of optimizations and transformations. Earlier stages can be
dumped with various debug options, such as --dump-nfa, --dump-dfa-raw
etc. (see the full list of options).
SEE ALSO
You can find more information about re2c at the official website:
http://re2c.org. Similar programs are flex(1), lex(1), quex(-
http://quex.sourceforge.net).
AUTHORS
Re2c was originaly written by Peter Bumbulis in 1993. Since then it
has been developed and maintained by multiple volunteers; mots notably,
Brain Young, Marcus Boerger, Dan Nuffer and Ulya Trofimovich.
VERSION INFORMATION
This manpage describes re2c version 1.3.
RE2C(1)