# RE2C (1) Manual Page

## NAME

re2c - convert regular expressions to C/C++

## SYNOPSIS

re2c [OPTIONS] FILE

## DESCRIPTION

re2c is a lexer generator for C/C++. It finds regular expression specifications inside of C/C++ comments and replaces them with a hard-coded DFA. The user must supply some interface code in order to control and customize the generated DFA.

## EXAMPLE

Given the following code:

    unsigned int stou (const char * s)
    {
    #   define YYCTYPE char
        const YYCTYPE * YYCURSOR = s;
        unsigned int result = 0;

        for (;;)
        {
            /*!re2c
                re2c:yyfill:enable = 0;

                "\x00" { return result; }
                [0-9]  { result = result * 10 + c; continue; }
            */
        }
    }

`re2c -is` will generate:

    /* Generated by re2c 0.13.7.dev on Mon Jul 14 13:37:46 2014 */
    unsigned int stou (const char * s)
    {
    #   define YYCTYPE char
        const YYCTYPE * YYCURSOR = s;
        unsigned int result = 0;

        for (;;)
        {

    {
            YYCTYPE yych;

            yych = *YYCURSOR;
            if (yych <= 0x00) goto yy3;
            if (yych <= '/') goto yy2;
            if (yych <= '9') goto yy5;
    yy2:
    yy3:
            ++YYCURSOR;
            { return result; }
    yy5:
            ++YYCURSOR;
            { result = result * 10 + c; continue; }
    }

        }
    }

## OPTIONS

-?, -h

  Invoke a short help.

-b

  Implies -s. Use bit vectors as well in the attempt to coax better code out of the compiler. Most useful for specifications with more than a few keywords (e.g. for most programming languages).

-c

  Used to support (f)lex-like condition support.

-d

  Creates a parser that dumps information about the current position and in which state the parser is while parsing the input. This is useful to debug parser issues and states. If you use this switch you need to define a macro YYDEBUG that is called like a function with two parameters: void YYDEBUG (int state, char current). The first parameter receives the state or -1 and the second parameter receives the input at the current cursor.

-D

  Emit Graphviz dot data. It can then be processed with e.g. `dot -Tpng input.dot > output.png`. Please note that scanners with many states may crash dot.

-e

  Generate a parser that supports EBCDIC. The generated code can deal with any character up to 0xFF. In this mode re2c assumes that input character size is 1 byte. This switch is incompatible with -w, -x, -u and -8.

-f

  Generate a scanner with support for storable state. For details see below at SCANNER WITH STORABLE STATES.

-F

  Partial support for flex syntax. When this flag is active then named definitions must be surrounded by curly braces and can be defined without an equal sign and the terminating semi colon. Instead names are treated as direct double quoted strings.

-g

  Generate a scanner that utilizes GCC’s computed goto feature. That is re2c generates jump tables whenever a decision is of a certain complexity (e.g. a lot of if conditions are otherwise necessary). This is only useable with GCC and produces output that cannot be compiled with any other compiler. Note that this implies -b and that the complexity threshold can be configured using the inplace configuration cgoto:threshold.

-i

  Do not output #line information. This is usefull when you want use a CMS tool with the re2c output which you might want if you do not require your users to have re2c themselves when building from your source.

-o OUTPUT

  Specify the output file.

-r

  Allows reuse of scanner definitions with /*!use:re2c after /*!rules:re2c. In this mode no /*!re2c block and exactly one /*!rules:re2c must be present. The rules are being saved and used by every /*!use:re2c block that follows. These blocks can contain inplace configurations, especially re2c:flags:e, re2c:flags:w, re2c:flags:x, re2c:flags:u and re2c:flags:8. That way it is possible to create the same scanner multiple times for different character types, different input mechanisms or different output mechanisms. The /*!use:re2c blocks can also contain additional rules that will be appended to the set of rules in /*!rules:re2c.

-s

  Generate nested ifs for some switches. Many compilers need this assist to generate better code.

-t

  Create a header file that contains types for the (f)lex-like condition support. This can only be activated when -c is in use.

-u

  Generate a parser that supports UTF-32. The generated code can deal with any valid Unicode character up to 0x10FFFF. In this mode re2c assumes that input character size is 4 bytes. This switch is incompatible with -e, -w, -x and -8. This implies -s.

-v

  Show version information.

-V

  Show the version as a number XXYYZZ.

-w

  Generate a parser that supports UCS-2. The generated code can deal with any valid Unicode character up to 0xFFFF. In this mode re2c assumes that input character size is 2 bytes. This switch is incompatible with -e, -x, -u and -8. This implies -s.

-x

  Generate a parser that supports UTF-16. The generated code can deal with any valid Unicode character up to 0x10FFFF. In this mode re2c assumes that input character size is 2 bytes. This switch is incompatible with -e, -w, -u and -8. This implies -s.

-1

  Force single pass generation, this cannot be combined with -f and disables YYMAXFILL generation prior to last re2c block.

-8

  Generate a parser that supports UTF-8. The generated code can deal with any valid Unicode character up to 0x10FFFF. In this mode re2c assumes that input character size is 1 byte. This switch is incompatible with -e, -w, -x and -u.

--case-insensitive

  All strings are case insensitive, so all "-expressions are treated in the same way '-expressions are.

--case-inverted

  Invert the meaning of single and double quoted strings. With this switch single quotes are case sensitive and double quotes are case insensitive.

--no-generation-date

  Suppress date output in the generated output so that it only shows the re2c version.

--encoding-policy POLICY

  Specify how re2c must treat Unicode surrogates. POLICY can be one of the following: fail (abort with error when surrogate encountered), substitute (silently substitute surrogate with error code point 0xFFFD), ignore (treat surrogates as normal code points). By default re2c ignores surrogates (for backward compatibility). Unicode standard says that standalone surrogates are invalid code points, but different libraries and programs treat them differently.

## INTERFACE CODE

The user must supply interface code either in the form of C/C++ code (macros, functions, variables, etc.) or in the form of inplace configurations. Which symbols must be defined and which are optional depends on a particular use case.

YYCONDTYPE

  In -c mode you can use -t to generate a file that contains the enumeration used as conditions. Each of the values refers to a condition of a rule set.

YYCTXMARKER

  l-value of type * YYCTYPE. The generated code saves trailing context backtracking information in YYCTXMARKER. The user only needs to define this macro if a scanner specification uses trailing context in one or more of its regular expressions.

YYCTYPE

  Type used to hold an input symbol (code unit). Usually char or unsigned char for ASCII, EBCDIC and UTF-8, unsigned short for UTF-16 or UCS-2 and unsigned int for UTF-32.

YYCURSOR

  l-value of type * YYCTYPE that points to the current input symbol. The generated code advances YYCURSOR as symbols are matched. On entry, YYCURSOR is assumed to point to the first character of the current token. On exit, YYCURSOR will point to the first character of the following token.

YYDEBUG (state, current)

  This is only needed if the -d flag was specified. It allows to easily debug the generated parser by calling a user defined function for every state. The function should have the following signature: void YYDEBUG (int state, char current). The first parameter receives the state or -1 and the second parameter receives the input at the current cursor.

YYFILL (n)

  The generated code “calls” YYFILL (n) when the buffer needs (re)filling: at least n additional characters should be provided. YYFILL (n) should adjust YYCURSOR, YYLIMIT, YYMARKER and YYCTXMARKER as needed. Note that for typical programming languages n will be the length of the longest keyword plus one. The user can place a comment of the form /*!max:re2c*/ once to insert a YYMAXFILL (n) definition that is set to the maximum length value. If -1 switch is used then YYMAXFILL can be triggered only once after the last /*!re2c ... */ block.

YYGETCONDITION ()

  This define is used to get the condition prior to entering the scanner code when using -c switch. The value must be initialized with a value from the enumeration YYCONDTYPE type.

YYGETSTATE ()

  The user only needs to define this macro if the -f flag was specified. In that case, the generated code “calls” YYGETSTATE () at the very beginning of the scanner in order to obtain the saved state. YYGETSTATE () must return a signed integer. The value must be either -1, indicating that the scanner is entered for the first time, or a value previously saved by YYSETSTATE (s). In the second case, the scanner will resume operations right after where the last YYFILL (n) was called.

YYLIMIT

  Expression of type * YYCTYPE that marks the end of the buffer (YYLIMIT[-1] is the last character in the buffer). The generated code repeatedly compares YYCURSOR to YYLIMIT to determine when the buffer needs (re)filling.

YYMARKER

  l-value of type * YYCTYPE. The generated code saves backtracking information in YYMARKER. Some easy scanners might not use this.

YYMAXFILL

  This will be automatically defined by /*!max:re2c*/ blocks as explained above.

YYSETCONDITION (c)

  This define is used to set the condition in transition rules. This is only being used when -c is active and transition rules are being used.

YYSETSTATE (s)

  The user only needs to define this macro if the -f flag was specified. In that case, the generated code “calls” YYSETSTATE just before calling YYFILL (n). The parameter to YYSETSTATE is a signed integer that uniquely identifies the specific instance of YYFILL (n) that is about to be called. Should the user wish to save the state of the scanner and have YYFILL (n) return to the caller, all he has to do is store that unique identifer in a variable. Later, when the scannered is called again, it will call YYGETSTATE () and resume execution right where it left off. The generated code will contain both YYSETSTATE (s) and YYGETSTATE even if YYFILL (n) is being disabled.

## SYNTAX

Code for re2c consists of a set of rules, named definitions and inplace configurations.

rules consist of a regular-expressions along with a block of C/C++ code that is to be executed when the associated regular-expression is matched. You can either start the code with an opening curly brace or the sequence :=. When the code with a curly brace then re2c counts the brace depth and stops looking for code automatically. Otherwise curly braces are not allowed and re2c stops looking for code at the first line that does not begin with whitespace. If two or more rules overlap, the first rule is preferred.

regular-expression { C/C++ code }

regular-expression := C/C++ code

There is one special rule: default rule *:

* { C/C++ code }

* := C/C++ code

Note | [^] differs from *: * has the lowest priority, matches any code unit (either valid or invalid) and always consumes one character; [^] matches any valid code point (not code unit) and can consume multiple characters. In fact, when variable-length encoding is used, * is the only possible way to match invalid input character.

If -c is active then each regular-expression is preceeded by a list of comma separated condition names. Besides normal naming rules there are two special cases. A rule may contain the single condition name * and no contition name at all. In the latter case the rule cannot have a regular-expression. Non empty rules may further more specify the new condition. In that case re2c will generated the necessary code to change the condition automatically. Just as above code can be started with a curly brace of the sequence :=. Further more rules can use :=> as a shortcut to automatically generate code that not only sets the new condition state but also continues execution with the new state. A shortcut rule should not be used in a loop where there is code between the start of the loop and the re2c block unless re2c:cond:goto is changed to continue. If code is necessary before all rule (though not simple jumps) you can doso by using <! pseudo-rules.

<condition-list> regular-expression { C/C++ code }

<condition-list> regular-expression := C/C++ code

<condition-list> * { C/C++ code }

<condition-list> * := C/C++ code

<condition-list> regular-expression => condition { C/C++ code }

<condition-list> regular-expression => condition := C/C++ code

<condition-list> regular-expression :=> condition

<*> regular-expression { C/C++ code }

<*> regular-expression := C/C++ code

<*> * { C/C++ code }

<*> * := C/C++ code

<*> regular-expression => condition { C/C++ code }

<*> regular-expression => condition := C/C++ code

<*> regular-expression :=> condition

<> { C/C++ code }

<> := C/C++ code

<> => condition { C/C++ code }

<> => condition := C/C++ code

<> :=> condition

<!condition-list> { C/C++ code }

<!condition-list> := C/C++ code

<!*> { C/C++ code }

<!*> := C/C++ code

named definitions are of the form:

name = regular-expression;

If -F is active, then named definitions are also of the form:

name regular-expression

inplace configurations are of the form:

re2c:name = value;

re2c:name = “_value_”;

## REGULAR EXPRESSIONS

“foo”

  literal string “foo”. ANSI-C escape sequences can be used.

‘foo’

  literal string “foo” (characters [a-zA-Z] treated case-insensitive). ANSI-C escape sequences can be used.

[xyz]

  character class; in this case, regular-expression matches either ‘x’, ‘y’, or ‘z’.

[abj-oZ]

  character class with a range in it; matches ‘a’, ‘b’, any letter from ‘j’ through ‘o’ or ‘Z’.

[^class]

  inverted character class.

r \ s

  match any r which isn’t s. r and s must be regular-expressions which can be expressed as character classes.

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).

name

  the expansion of the named definition.

( r )

  r; parentheses are used to override precedence.

r s

  r followed by s (concatenation).

r | s

  either r or s (alternative).

r / s

  r but only if it is followed by s. Note that s is not part of the matched text. This type of regular-expression is called “trailing context”. Trailing context can only be the end of a rule and not part of a named definition.

r { n }

  matches r exactly n times.

r { n , }

  matches r at least n times.

r { n , m }

  matches r at least n times, but not more than m times.

.

  match any character except newline.

def

  matches named definition as specified by def only if -F is off. If -F is active then this behaves like it was enclosed in double quotes and matches the string “def”.

Character classes and string literals may contain octal or hexadecimal character definitions and the following set of escape sequences: \a, \b, \f, \n, \r, \t, \v, \\. An octal character is defined by a backslash followed by its three octal digits (e.g. \377). Hexadecimal characters from 0 to 0xFF are defined by backslash, a lower cased ‘x’ and two hexadecimal digits (e.g. \x12). Hexadecimal characters from 0x100 to 0xFFFF are defined by backslash, a lower cased ‘u’ (or an upper cased ‘X’) and four hexadecimal digits (e.g. \u1234). Hexadecimal characters from 0x10000 to 0xFFFFffff are defined by backslash, an upper cased ‘U’ and eight hexadecimal digits (e.g. \U12345678).

The only portable “any” rule is the default rule *.

## INPLACE CONFIGURATIONS

It is possible to configure code generation inside re2c blocks. The following lists the available configurations:

re2c:condprefix = yyc_;

  Allows to specify the prefix used for condition labels. That is this text is prepended to any condition label in the generated output file.

re2c:condenumprefix = yyc;

  Allows to specify the prefix used for condition values. That is this text is prepended to any condition enum value in the generated output file.

re2c:cond:divider = “/* *********************************** */”;

  Allows to customize the devider for condition blocks. You can use ‘@@’ to put the name of the condition or ustomize the placeholder using re2c:cond:divider@cond.

re2c:cond:divider@cond = @@;

  Specifies the placeholder that will be replaced with the condition name in re2c:cond:divider.

re2c:cond:goto = “goto @@;”;

  Allows to customize the condition goto statements used with :=> style rules. You can use ‘@@’ to put the name of the condition or ustomize the placeholder using re2c:cond:goto@cond. You can also change this to ‘continue;’, which would allow you to continue with the next loop cycle including any code between loop start and re2c block.

re2c:cond:goto@cond = @@;

  Spcifies the placeholder that will be replaced with the condition label in re2c:cond:goto.

re2c:indent:top = 0;

  Specifies the minimum number of indendation to use. Requires a numeric value greater than or equal zero.

re2c:indent:string = “\t”;

  Specifies the string to use for indendation. Requires a string that should contain only whitespace unless you need this for external tools. The easiest way to specify spaces is to enclude them in single or double quotes. If you do not want any indendation at all you can simply set this to “”.

re2c:yych:conversion = 0;

  When this setting is non zero, then re2c automatically generates conversion code whenever yych gets read. In this case the type must be defined using re2c:define:YYCTYPE.

re2c:yych:emit = 1;

  Generation of yych can be suppressed by setting this to 0.

re2c:yybm:hex = 0;

  If set to zero then a decimal table is being used else a hexadecimal table will be generated.

re2c:yyfill:enable = 1;

  Set this to zero to suppress generation of YYFILL (n). When using this be sure to verify that the generated scanner does not read behind input. Allowing this behavior might introduce sever security issues to you programs.

re2c:yyfill:check = 1;

  This can be set 0 to suppress output of the pre condition using YYCURSOR and YYLIMIT which becomes usefull when YYLIMIT + max (YYFILL) is always accessible.

re2c:yyfill:parameter = 1;

  Allows to suppress parameter passing to YYFILL calls. If set to zero then no parameter is passed to YYFILL. However define:YYFILL@LEN allows to specify a replacement string for the actual length value. If set to a non zero value then YYFILL usage will be followed by the number of requested characters in braces unless re2c:define:YYFILL:naked is set. Also look at re2c:define:YYFILL:naked and re2c:define:YYFILL@LEN.

re2c:startlabel = 0;

  If set to a non zero integer then the start label of the next scanner blocks will be generated even if not used by the scanner itself. Otherwise the normal yy0 like start label is only being generated if needed. If set to a text value then a label with that text will be generated regardless of whether the normal start label is being used or not. This setting is being reset to 0 after a start label has been generated.

re2c:labelprefix = yy;

  Allows to change the prefix of numbered labels. The default is yy and can be set any string that is a valid label.

re2c:state:abort = 0;

  When not zero and switch -f is active then the YYGETSTATE block will contain a default case that aborts and a -1 case is used for initialization.

re2c:state:nextlabel = 0;

  Used when -f 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 startlabel to force a specific start label or default to yy0 as 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:cgoto:threshold = 9;

  When -g is active this value specifies the complexity threshold that triggers generation of jump tables rather than using nested if’s and decision bitfields. The threshold is compared against a calculated estimation of if-s needed where every used bitmap divides the threshold by 2.

re2c:yych:conversion = 0;

  When the input uses signed characters and -s or -b switches are in effect re2c allows to automatically convert to the unsigned character type that is then necessary for its internal single character. When this setting is zero or an empty string the conversion is disabled. Using a non zero number the conversion is taken from YYCTYPE. If that is given by an inplace configuration that value is being used. Otherwise it will be (YYCTYPE) and changes to that configuration are no longer possible. When this setting is a string the braces must be specified. Now assuming your input is a char * buffer and you are using above mentioned switches you can set YYCTYPE to unsigned char and this setting to either 1 or (unsigned char).

re2c:define:define:YYCONDTYPE = YYCONDTYPE;

  Enumeration used for condition support with -c mode.

re2c:define:YYCTXMARKER = YYCTXMARKER;

  Allows to overwrite the define YYCTXMARKER and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYCTYPE = YYCTYPE;

  Allows to overwrite the define YYCTYPE and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYCURSOR = YYCURSOR;

  Allows to overwrite the define YYCURSOR and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYDEBUG = YYDEBUG;

  Allows to overwrite the define YYDEBUG and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYFILL = YYFILL;

  Allows to overwrite the define YYFILL and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYFILL:naked = 0;

  When set to 1 neither braces, parameter nor semicolon gets emitted.

re2c:define:YYFILL@len = @@;

  When using re2c:define:YYFILL and re2c:yyfill:parameter is 0 then any occurence of this text inside YYFILL will be replaced with the actual length value.

re2c:define:YYGETCONDITION = YYGETCONDITION;

  Allows to overwrite the define YYGETCONDITION.

re2c:define:YYGETCONDITION:naked = 0;

  When set to 1 neither braces, parameter nor semicolon gets emitted.

re2c:define:YYGETSTATE = YYGETSTATE;

  Allows to overwrite the define YYGETSTATE and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYGETSTATE:naked = 0;

  When set to 1 neither braces, parameter nor semicolon gets emitted.

re2c:define:YYLIMIT = YYLIMIT;

  Allows to overwrite the define YYLIMIT and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYMARKER = YYMARKER;

  Allows to overwrite the define YYMARKER and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYSETCONDITION = YYSETCONDITION;

  Allows to overwrite the define YYSETCONDITION.

re2c:define:YYSETCONDITION@cond = @@;

  When using re2c:define:YYSETCONDITION then any occurence of this text inside YYSETCONDITION will be replaced with the actual new condition value.

re2c:define:YYSETSTATE = YYSETSTATE;

  Allows to overwrite the define YYSETSTATE and thus avoiding it by setting the value to the actual code needed.

re2c:define:YYSETSTATE:naked = 0;

  When set to 1 neither braces, parameter nor semicolon gets emitted.

re2c:define:YYSETSTATE@state = @@;

  When using re2c:define:YYSETSTATE then any occurence of this text inside YYSETSTATE will be replaced with the actual new state value.

re2c:label:yyFillLabel = yyFillLabel;

  Allows to overwrite the name of the label yyFillLabel.

re2c:label:yyNext = yyNext;

  Allows to overwrite the name of the label yyNext.

re2c:variable:yyaccept = yyaccept;

  Allows to overwrite the name of the variable yyaccept.

re2c:variable:yybm = yybm;

  Allows to overwrite the name of the variable yybm.

re2c:variable:yych = yych;

  Allows to overwrite the name of the variable yych.

re2c:variable:yyctable = yyctable;

  When both -c and -g are active then re2c uses this variable to generate a static jump table for YYGETCONDITION.

re2c:variable:yystable = yystable;

  When both -f and -g are active then re2c uses this variable to generate a static jump table for YYGETSTATE.

re2c:variable:yytarget = yytarget;

  Allows to overwrite the name of the variable yytarget.

## SCANNER WITH STORABLE STATES

When the -f flag is specified, re2c generates a scanner that can store its current state, return to the caller, and later resume operations exactly where it left off.

The default operation of re2c is a “pull” model, where the scanner asks for extra input whenever it needs it. However, this mode of operation assumes that the scanner is the “owner” the parsing loop, and that may not always be convenient.

Typically, if there is a preprocessor ahead of the scanner in the stream, or for that matter any other procedural source of data, the scanner cannot “ask” for more data unless both scanner and source live in a separate threads.

The -f flag is useful for just this situation: it lets users design scanners that work in a “push” model, i.e. where data is fed to the scanner chunk by chunk. When the scanner runs out of data to consume, it just stores its state, and return to the caller. When more input data is fed to the scanner, it resumes operations exactly where it left off.

When using the -f option re2c does not accept stdin because it has to do the full generation process twice which means it has to read the input twice. That means re2c would fail in case it cannot open the input twice or reading the input for the first time influences the second read attempt.

Changes needed compared to the “pull” model:

1. User has to supply macros YYSETSTATE () and YYGETSTATE (state).

2. The -f option inhibits declaration of yych and yyaccept. So the user has to declare these. Also the user has to save and restore these. In the example examples/push.re these are declared as fields of the (C\++) class of which the scanner is a method, so they do not need to be saved/restored explicitly. For C they could e.g. be made macros that select fields from a structure passed in as parameter. Alternatively, they could be declared as local variables, saved with YYFILL (n) when it decides to return and restored at entry to the function. Also, it could be more efficient to save the state from YYFILL (n) because YYSETSTATE (state) is called unconditionally. YYFILL (n) however does not get state as parameter, so we would have to store state in a local variable by YYSETSTATE (state).

3. Modify YYFILL (n) to return (from the function calling it) if more input is needed.

4. Modify caller to recognise “more input is needed” and respond appropriately.

5. The generated code will contain a switch block that is used to restores the last state by jumping behind the corrspoding YYFILL (n) call. This code is automatically generated in the epilog of the first /*!re2c */ block. It is possible to trigger generation of the YYGETSTATE () block earlier by placing a /*!getstate:re2c*/ comment. This is especially useful when the scanner code should be wrapped inside a loop.

Please see examples/push.re for push-model scanner. The generated code can be tweaked using inplace configurations state:abort and state:nextlabel.

## SCANNER WITH CONDITION SUPPORT

You can preceed regular expressions with a list of condition names when using the -c switch. In this case re2c generates scanner blocks for each conditon. Where each of the generated blocks has its own precondition. The precondition is given by the interface define YYGETCONDITON() and must be of type YYCONDTYPE.

There are two special rule types. First, the rules of the condition * are merged to all conditions. And second the empty condition list allows to provide a code block that does not have a scanner part. Meaning it does not allow any regular expression. The condition value referring to this special block is always the one with the enumeration value 0. This way the code of this special rule can be used to initialize a scanner. It is in no way necessary to have these rules: but sometimes it is helpful to have a dedicated uninitialized condition state.

Non empty rules allow to specify the new condition, which makes them transition rules. Besides generating calls for the define YYSETCONDTITION no other special code is generated.

There is another kind of special rules that allow to prepend code to any code block of all rules of a certain set of conditions or to all code blocks to all rules. This can be helpful when some operation is common among rules. For instance this can be used to store the length of the scanned string. These special setup rules start with an exclamation mark followed by either a list of conditions <! condition, ... > or a star <!*>. When re2c generates the code for a rule whose state does not have a setup rule and a star’d setup rule is present, than that code will be used as setup code.

## ENCODINGS

re2c supports the following encodings: ASCII (default), EBCDIC (-e), UCS-2 (-w), UTF-16 (-x), UTF-32 (-u) and UTF-8 (-8). ASCII is default. You can either pass cmd flag or use inplace configuration in the form re2c:flags.

The following concepts should be clarified when talking about encoding. Code point is an abstract number, which represents single encoding symbol. 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 can be needed to represent a single code point, depending on the encoding. In fixed-length encoding, each code point is represented with equal number of code units. In variable-length encoding, different code points can be represented with different number of code units.

ASCII

  is a fixed-length encoding. Its code space includes 0x100 code points, from 0 to 0xFF (note that this is re2c-specific understanding of ASCII). One code point is represented with exactly one 1-byte code unit, which has the same value as the code point. Size of YYCTYPE must be 1 byte.

EBCDIC

  is a fixed-length encoding. Its code space includes 0x100 code points, from 0 to 0xFF. One code point is represented with exactly one 1-byte code unit, which has the same value as the code point. Size of YYCTYPE must be 1 byte.

UCS-2

  is a fixed-length encoding. Its code space includes 0x10000 code points, from 0 to 0xFFFF. One code point is represented with exactly one 2-byte code unit, which has the same value as the code point. Size of YYCTYPE must be 2 bytes.

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. Size of YYCTYPE must be 2 bytes.

UTF-32

  is a fixed-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 exactly one 4-byte code unit. Size of YYCTYPE must be 4 bytes.

UTF-8

  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 sequence of one, two, three or four 1-byte code units. Size of YYCTYPE must be 1 bytes.

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 sequences with --encoding-policy policy flag (see OPTIONS section for full explanation).

For some encodings, there are code units, that never occur in valid encoded stream (e.g. 0xFF byte in UTF-8). If the generated scanner must check for invalid input, the only true way to do so is to use default rule *. Note, that full range rule [^] won’t catch invalid code units when variable-length encoding is used ([^] means “all valid code points”, while default rule * means “all possible code units”: see Note about default rule in SYNTAX section).

## GENERIC INPUT API

re2c usually operates on input using pointer-like primitives YYCURSOR, YYMARKER, YYCTXMARKER and YYLIMIT.

Generic input API (enabled with --input custom switch) allows to customize input operations. In this mode, re2c will express all operations on input in terms of the following primitives:

1. YYPEEK () --- get current input character

2. YYSKIP () --- advance to the next character

3. YYBACKUP () --- backup current input position

4. YYBACKUPCTX () --- backup current input position for trailing context

5. YYRESTORE () --- restore current input position

6. YYRESTORECTX () --- restore current input position for trailing context

7. YYLESSTHAN (n) --- check if less than n input characters are left

This article (http://skvadrik.github.io/aleph_null/posts/re2c/2015-01-13-input_model.html) has more details, and you can find some usage examples: http://skvadrik.github.io/aleph_null/posts/re2c/2015-01-15-input_model_custom.html .

## UNDERSTANDING RE2C

The subdirectory lessons of the re2c distribution contains a few step by step lessons to get you started with re2c. All examples in the lessons subdirectory can be compiled and actually work.

## BUGS

1. Difference only works for character sets, and not in UTF-8 mode.

2. The generated DFA is not minimal.

3. Features, that are naturally orthogonal (such as reusable rules, conditions, setup rules and default rules), cannot always be combined. E.g., one cannot set setup/default rule for condition in scanner with reusable rules.

4. re2c does too much unnecessary work: e.g., if /*!use:re2c ... */ block has additional rules, these rules are parsed 4 times, while they should be parsed only once.

5. The re2c internal algorithms need documentation.

## SEE ALSO

flex(1), lex(1), quex (http://quex.sourceforge.net)

More information on re2c can be found here: http://re2c.org/.

## AUTHORS

1. Peter Bumbulis peter@csg.uwaterloo.ca

2. Brian Young bayoung@acm.org

3. Dan Nuffer nuffer@users.sourceforge.net

4. Marcus Boerger helly@users.sourceforge.net

5. Hartmut Kaiser hkaiser@users.sourceforge.net

6. Emmanuel Mogenet mgix@mgix.com (added storable state)

7. Ulya Trofimovich skvadrik@gmail.com

## VERSION INFORMATION

This manpage describes re2c, version 0.14.3, package date 20 May 2015.