What is Lex explain with an example?

What is Lex explain with an example?

Lex is a program designed to generate scanners, also known as tokenizers, which recognize lexical patterns in text. It is easy, for example, to interface Lex and Yacc, an open source program that generates code for the parser in the C programming language.

What is use of Yylex and Yywrap?

yylex() makes a call to yywrap() when it encounters the end of input. If yywrap() returns zero (indicating false) yylex() assumes there is more input and it continues scanning from the location pointed to by yyin.

What is Yyin and Yyout?

yyin. A variable that determines the input stream for the yylex() and input functions. yyout. A variable that determines the output stream for the output macro, which processes input that does not match any rules.

How do you write Lex and YACC programs?

For Compiling YACC Program:

  1. Write lex program in a file file. l and yacc in a file file. y.
  2. Open Terminal and Navigate to the Directory where you have saved the files.
  3. type lex file. l.
  4. type yacc file. y.
  5. type cc lex. yy. c y. tab. h -ll.
  6. type ./a. out.

What is the use of lex?

Lex is a program that generates lexical analyzer. It is used with YACC parser generator. The lexical analyzer is a program that transforms an input stream into a sequence of tokens. It reads the input stream and produces the source code as output through implementing the lexical analyzer in the C program.

Why is Yylex used?

yylex() returns a value indicating the type of token that has been obtained. If the token has an actual value, this value (or some representation of the value, for example, a pointer to a string containing the value) is returned in an external variable named yylval.

Why is Yywrap used?

Function yywrap is called by lex when input is exhausted. Return 1 if you are done or 0 if more processing is required. Every C program requires a main function. The input file for lex is yyin and defaults to stdin .