Flex stands for fast lexical analyzer generator, it is a computer application that is used to generate lexical analyzers for the programs written in lex language. The main work of the lexical analyzer is to convert the program into a sequence of tokens. It is developed by Vern Paxson. It is free software written in C language and can be run on different platforms like Linux, Unix, windows, mac, etc. Its initial release was in 1987 and its first stable release was in 2017. Flex has a limitation to generating code for C and C++ only.
YACC stands for yet another compiler, it is a parser generator that is used with lex to generate parsers of lex files. It uses LALR(1) parsing technique, LALR means to look ahead left to right and 1 shows that rightmost derivation is used with 1 lookahead token.
Format of a Lex file:
There are 3 main components of a lex file :
- Definition Section: The first section is the definition section, this section is used to include libraries and header files for the program. This section is able to accept code written in C.
Example of Definition Section:
%{
#include <stdio.h>
#include<conio.h>
%}- Rule Section: The second section is the rule section, the main work of this section is to match patterns by using regular expressions written in this section.
Example of Rule Section:
%% [a-zA-Z] this pattern will search for alphabets in lower and upper case %%
- Code Section: This is the last section that is used to write all the logic, functions, and statements for the program. This code is written in C language. The program will have all the functionalities of a C program.
Example of Code Section:
int main()
{
yylex();
return 0;
}Working of Flex:
Installing Flex on Windows:
Follow the below steps to install Flex on Windows:
Step 1: Visit this URL using any web browser.
Step 2: On this page, all the features and minimum requirement of the system to install flex is given. Here the download link of the flex program for Windows XP, 7, 8, etc is given. Click on the download link, downloading of the executable file will start shortly. It is a small 30.19 MB file that will hardly take a minute.
Step 3: Now check for the executable file in downloads in your system and run it.
Step 4: It will prompt confirmation to make changes to your system. Click on Yes.
Step 5: Setup screen will appear, click on Next.
Step 6: The next screen will be of License Agreement, click on I Agree.
Step 7: The next screen will be of installing location so choose the drive which will have sufficient memory space for installation. It needed only a memory space of 176.7 MB.
Step 8: Next screen will be of choosing the Start menu folder so don’t do anything just click on the Next Button.
Step 9: After this installation process will start and will hardly take a minute to complete the installation.
Step 10: Click on Finish after the installation process is complete. Keep the tick mark on the checkbox if you want to run Flex now if not then uncheck it.
Step 11: Flex Windows is successfully installed on the system and an icon is created on the desktop
Step 12: Run the software and see the interface.
Congratulations!! At this point, you have successfully installed Flex on your windows system.