C program to detect tokens in a C program - GeeksforGeeks.
Generating a Lexical Analyzer Program. lex generates a C-language scanner from a source specification that you write. This specification contains a list of rules indicating sequences of characters -- expressions -- to be searched for in an input text, and the actions to take when an expression is found.
In stead of writing a scanner from scratch, you only need to identify the vocabulary of a certain language (e.g. Simple), write a specification of patterns using regular expressions (e.g. DIGIT (0-9)), and FLEX will construct a scanner for you.
Since the function of the lexical analyzer is to scan the source program and produce a stream of tokens as output, the issues involved in the design of lexical analyzer are: 1. Identifying the tokens of the language for which the lexical analyzer is to be built, and to specify these tokens by using suitable notation, and 2. Constructing a suitable recognizer for these tokens.
Lex - A Lexical Analyzer Generator M. E. Lesk and E. Schmidt ABSTRACT Lex helps write programs whose control flow is directed by instances of regular expressions in the input stream. It is well suited for editor-script type transformations and for segmenting input in preparation for a parsing routine.
The lexer, also called lexical analyzer or tokenizer, is a program that breaks down the input source code into a sequence of lexemes. It reads the input source code character by character, recognizes the lexemes and outputs a sequence of tokens describing the lexemes.
There are three general approaches for the implementation of a lexical analyzer: (i) By using a lexical-analyzer generator, such as lex compiler to produce the lexical analyzer from a regular expression based specification. In this, the generator provides routines for reading and buffering the input.
Lexical analysis: process of taking an input string of characters (such as the source code of a computer program) and producing a sequence of symbols called lexical tokens, or just tokens, which may be handled more easily by a parser. The lexical analyzer reads the source text and, thus, it may perform certain secondary tasks.