FLEX (Fast Lexical Analyzer Generator) is a tool/computer program for generating lexical analyzers (scanners or lexers) written by Vern Paxson in C around 1987. Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language. The function yylex() is the main flex function which runs the Rule Section. Prerequisite: FLEX (Fast Lexical Analyzer Generator) Example:
Input: hello how are you? Output: hellohowareyou? Input: Welcome to Geeks for Geeks Output: WelcometoGeeksforGeeks
Approach: Open input file in read mode and whenever parser encounters newline (\n), space ( ) or tab (\t) remove it and write all the other characters in output file. Input File: Input.txt (Input File used in this program)
Below is the implementation program:
/*Lex program to take input from file and remove multiple spaces, newline and tab and write output in a separate file*/ % { /*Definition section */
%
} /* Rule: whenever space, tab or newline is encountered, remove it*/ % % [ \n\t]+ { fprintf (yyout, "%s");}
. { fprintf (yyout, "%s", yytext); }
% % // driver code int main()
{ /* yyin and yyout as pointer
of File type */
extern FILE *yyin, *yyout;
/* yyin points to the file input.txt
and opens it in read mode*/
yyin = fopen ("Input.txt", "r");
/* yyout points to the file output.txt
and opens it in write mode*/
yyout = fopen ("Output.txt", "w");
yylex();
return 0;
} |
Output: