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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JFlex User’s Manual

This feature is still in alpha status, and not fully implemented yet. The rule expr3 can only be matched in state A and expr4 in states ABand C. Set difference –e.

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.

In flex more special characters lose their meaning in character classes. Both cause the scanning method to be declared as returning Java type int. The default end kexer file value under this setting is ,exerwhich is a public static final int member of the generated class.

Scanning binaries is both easier and more difficult than scanning text files. Set the initial size of the scan buffer to the specified value decimal, in bytes.


It is possible, but not considered good Java style to put helper classes, such as token ,anual, into this section; they are usually better declared in their own. The directive will be replaced verbatim by the contents of the specified manuall. Reader object which is passed to the lexer in the generated constructor. It assumes that you are familiar with the topic of lexical analysis in parsing. The next section of this manual describes installation procedures for JFlex.

flex: The Fast Lexical Analyzer has moved

The second part of the lexical specification contains options and directives to customise the generated lexer, declarations of lexical states and macro definitions. There are no special parser codeinit code or scan with options any ,exer that you have to provide in your CUP parser specification. If no return type is specified, the scanning method ldxer be declared as returning values of class Yytoken. A lexical state acts like a start condition.

Turns column counting on. If you provide your own constructor for the lexer, you should always chain-call the generated one to initialise the input buffer. Which letters are uppercase and which lowercase letters, is defined by the Unicode standard.

Causes the specified exceptions to be declared in the throws clause of the constructor. This can be useful in embedded and similar situations where traditional operating system or C runtime facilities may not be available.


The default end of file value under this setting is null.

Here, the customised part is mostly in the user code section. JFlex applies the following standard operator precedences in regular expression from highest to lowest:.

The name of the class is by default Yylex. Access to the generated class is expected to be mediated by user class code see next switch. Of course the encoding to use can also come from the data itself: JFlex comes with a skeleton file in the src directory that reflects exactly the internal, pre-compiled skeleton and can be used lwxer the -skel option. This section gives details about JFlex 1.

So the expression a abc! The lexical rules section of a JFlex specification contains a set of regular expressions and actions Java code that are executed when the scanner matches the associated regular expression.

Flex – a scanner generator

These classes will sometimes have to be listed manually. This section discusses Unicode and encodings, cross platform scanning, and how to deal with binary data. If more than one end of file code directive is present, the code will be concatenated in order of appearance in the specification.