01 Lex Introduction

Lex¶

Language translator, which converts

• from lex source program having regular expression, to match tokens in input string
• to a C program which has the function yylex() which is used to scan the input for tokens

This will be the source file for lexical analysis of a C program. It will take a C program as input.

We use regular expressions to match lexemes and generate tokens

Lex Source Code¶

%{
#include
C Declarations
%}
Lex Symbols
%%
Rule
%%
Auxilliary functions (optional)

Simplest Program¶

Default program which copies input to output

%%
%%

Compilation¶

lex analyzer.l
cc lex.yy.c -ll

Execution¶

a.out

// Takes user input

a.out < my_program.c > sample.txt

Variables¶

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