Table of Contents
What does lex and yacc do?
Lex is a lexical analysis tool that can be used to identify specific text strings in a structured way from source text. Yacc is a grammar parser; it reads text and can be used to turn a sequence of words into a structured format for processing.
What is the difference between lex & yacc?
The main difference between Lex and Yacc is that Lex is a lexical analyzer which converts the source program into meaningful tokens while Yacc is a parser that generates a parse tree from the tokens generated by Lex. Generally, a compiler is a software program that converts the source code into machine code.
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.
What is yacc in compiler design?
YACC stands for Yet Another Compiler Compiler. YACC is a program designed to compile a LALR (1) grammar. It is used to produce the source code of the syntactic analyzer of the language produced by LALR (1) grammar. The input of YACC is the rule or grammar and the output is a C program.
What is the difference between lex and Flex?
Flex is a tool for generating scanners and was developed by the same group that created gnu-emacs. Flex is a rewrite of the Unix lex tool, however, the two implementations do not share any code. – Run time: Flex also provides faster run time compared to lex. The run time is about two times faster.
What is begin in lex?
BEGIN(statename) just means enter the state statename. So what this lex snippet does is the following: If an “/*” is read it enters the state C_COMMENT, when it sees a “*/” it goes back to the default state.
How do you write lex and YACC programs?
For Compiling YACC Program:
- Write lex program in a file file. l and yacc in a file file. y.
- Open Terminal and Navigate to the Directory where you have saved the files.
- type lex file. l.
- type yacc file. y.
- type cc lex. yy. c y. tab. h -ll.
- type ./a. out.
How does lex and YACC work together?
lex and yacc often work well together for developing compilers. As noted, a program uses the lex-generated scanner by repeatedly calling the function yylex() . The parser, called yyparse() by yacc , then resumes control and makes another call to the lexical analyzer to get another token.
What is Yytext?
yytext holds the text matched by the current token. So yytext[0] holds the first character of the text matched by the current token. Sometimes you have a rule which can match different texts so you need to get the real text matched like for variable names or you have a rule to match all arithmetic operations.
What is the full form of yacc?
Cross-platform. Type. Command. Yacc (Yet Another Compiler-Compiler) is a computer program for the Unix operating system developed by Stephen C. Johnson.
How do you write Lex and YACC programs?
What is difference between Lex and Flex?
Flex is a rewrite of the Unix lex tool, however, the two implementations do not share any code. – Run time: Flex also provides faster run time compared to lex. The run time is about two times faster. – Table compression: The table created by flex is approximately 17 times smaller than that created by lex.