[GoLUG] I just made my first Flex lexical analyzer Hello World

[Steve Litt]

Hi all,

I just made my first Flex lexical analyzer Hello World, as follows:

====================================
%{ // START DEFINITIONS SECTION
#include <stdio.h>
%}

%% // TRANSITION DEFS TO RULES SECTION

[\n] printf(": Hello World!\n");	

%% // TRANSITION RULES TO CODE SECTION

int yywrap(){}
int main() {
   yylex(); //Call rules section
}
====================================

You compile the preceding hello.l file with flex to create C file
lex.yy.c . Then you compile lex.yy.c to create a.out. Finally, you
perform the following command:

cat | ./a.out

Then type a few words separated by newlines (hit the Enter key), and
then press Ctrl+D to send end of file. The result is output in which
your original lines are typed, and for each line, a colon, a space and
the phrase "Hello Word!" are appended.

Like I say, this useless program is simply a hello world.

My hope is that, in about 5 years, I'll be able to use flex and its
semi-companion bison to create a parser for an incredibly easy keyboard
friendly book authoring system superior to LyX, and much more flexible
than Markdown or AsciiDoc.

SteveT
 

SteveT

Steve Litt 

Autumn 2023 featured book: Rapid Learning for the 21st Century
http://www.troubleshooters.com/rl21