PLEASE READ MY NOTE FIRST. Note: The following are the contents of a flex file that will be used to implement a lexical analyzer for a subset of the C programming language. I cannot understand anything in the code given below, so I need your help. I need you to explain every section of the code to me step-by-step in detail. At the end, please summarize what the code is all about and how it is functioning. Here's the code from the Flex file: %option noyywrap %{ #include using namespace std; ofstream yyoutlog; //output filestream for log file string loglist = ""; //list of tokens along with line numbers // define necessary c++ variables and functions here (if any) int lines = 1; %} /* Regular Definitions / delim [ \t\v\r] / write regular expressions for whitespace and newline / ws newline letter_ [A-Za-z_] digit [0-9] / write regular expressions for id, float and integers / id %% {ws} { / ignore whitespace / } {newline} { / do necessary bookkeeping (line number tracking etc.) */ } {id} { loglist="Line no "+to_string(lines)+": Token Lexeme "+yytext+" found"+"\n"+"\n"; yyoutlog< Lexeme "+yytext+" found"+"\n"+"\n"; yyoutlog< Lexeme "+yytext+" found"+"\n"+"\n"; yyoutlog< Lexeme "+yytext+" found"+"\n"+"\n"; yyoutlog<

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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PLEASE READ MY NOTE FIRST.

Note: The following are the contents of a flex file that will be used to implement a lexical analyzer for a subset of the C programming language. I cannot understand anything in the code given below, so I need your help. I need you to explain every section of the code to me step-by-step in detail. At the end, please summarize what the code is all about and how it is functioning.

Here's the code from the Flex file:

%option noyywrap

#include<bits/stdc++.h>

using namespace std;

ofstream yyoutlog; //output filestream for log file

string loglist = ""; //list of tokens along with line numbers

// define necessary c++ variables and functions here (if any)

int lines = 1;

/* Regular Definitions */

delim [ \t\v\r]

/* write regular expressions for whitespace and newline */

newline

letter_ [A-Za-z_]

digit [0-9]

/* write regular expressions for id, float and integers */

{ws} { /* ignore whitespace */ }

{newline} {

/* do necessary bookkeeping (line number tracking etc.) */

}

{id} {

loglist="Line no "+to_string(lines)+": Token <ID> Lexeme "+yytext+" found"+"\n"+"\n";

yyoutlog<<loglist;

}

if {

loglist="Line no "+to_string(lines)+": Token <IF> Lexeme "+yytext+" found"+"\n"+"\n";

yyoutlog<<loglist;

}

while {

loglist="Line no "+to_string(lines)+": Token <WHILE> Lexeme "+yytext+" found"+"\n"+"\n";

yyoutlog<<loglist;

}

"+"|"-" { /* to match two same operators use | */

loglist="Line no "+to_string(lines)+": Token <ADDOP> Lexeme "+yytext+" found"+"\n"+"\n";

yyoutlog<<loglist;

}

int main(int argc, char *argv[])

{

if(argc != 2) //check if file name is given

{

cout<<"Please input file name"<<endl;

return 0;

}

yyin = fopen(argv[1], "r"); //the file to be read must be assigned to yyin

yyoutlog.open("my_log.txt", ios::trunc); // remember to rename the log file as mentioned in the spec

if(yyin == NULL) // file does not exist

{

// print error message and exit

}

yylex(); // start reading the input file in a loop

//print total number of lines found in the input file

yyoutlog.close(); // close the log file

fclose(yyin); // close the input file

}

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