Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are .. BSD and the GNU Project also distribute flex (Fast Lexical Analyzer Generator), “ a. The flex project has moved: The project repository is now hosted at github: https:// Releases can be found at. Flexc++ reads one or more input files (called `lexer’ in this manual), Flexc++ is highly comparable to the programs flex and flex++, written by Vern Paxson.

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User installation works exactly the same way — just choose a directory where you have write permission. They will be ignored by JFlex.

To meet this requirement, an implementation shall extend the word boundary mechanism so that: If you have used the -symbol command line switch of CUP to change the name of the generated symbol interface, you have to tell JFlex about this change of interface so that correct end-of-file code is generated. First of all the Jay code in a file MiniParser. File a file name, either absolute or relative to the directory containing the lexical specification.

flex: The Fast Lexical Analyzer has moved

The cases of fixed-length look-ahead and fixed-length base expressions are handled efficiently by matching the concatenation and then pushing back the required amount of characters. To overcome this issue there are options that Flex provides in order to achieve reentrancy.


The set of lexical states associated with a regular expression is the StateList that precedes the expression. You can just concentrate on your grammar. References Aho, Alfred V.

JFlex User’s Manual

In that way, we get for input break the keyword break and not an Identifier break. You can easily port such a JLex specification to JFlex by replacing every!

In addition to regular expression matches, one can use lexical states to refine a specification. See also Encodings for more information on character sets, encodings, and scanning text vs. Causes the generated scanner to throw an instance of the specified exception in case of an internal error default is java.

Flex (lexical analyser generator)

The currently active lexical state of the scanner can be changed from within an action of a regular expression using the method yybegin. If an action does not return a value, the scanning process is resumed immediately after executing the action.

These classes will sometimes have to be listed manually. This feature is still in alpha status, and not fully implemented yet. StringCharacter an escape sequence or any unicode character that is not one of these meta characters: When in doubt or when requirements are not or not yet fixed: The input buffer of the lexer is connected with external input through the java.

Character an escape sequence or any unicode character that is not one of these meta characters: While there is no backtracking for expressions like a b in JFlex, some backtracking is still introduced by the longest match rule and occurs for instance on this set of expressions:.


JFlex will warn in this case and generate an additional default constructor without these parameters and without user init code which might potentially refer to the parameters. The section on Lexical specifications presents all JFlex options and the complete specification syntax; Encodings, Platforms, and Unicode provides information about Unicode and scanning text vs.

JFlex was designed to read old JLex specifications unchanged and to generate a scanner which behaves exactly the same as the one generated by JLex with the only difference of being faster.

The syntax is based on the use of regular expressions. Actions in the specification can then return Integer values as tokens.

Flexc++ (Version ) User Guide

Of course the encoding to use can also come from the data itself: From Wikipedia, the free encyclopedia. Since user code is part of the same class, JFlex has no language means like the private modifier to indicate which members and methods are internal and which ones belong to the API. As long as one encoding is used consistently, this is no problem. If something goes wrong, it returns -1 to indicate an error.

The int member variable yyline contains the number of lines starting with 0 from the beginning of input to the beginning of the current token.