Scanner Programs Using LEX

Compiler Construction Lab Manual / Scanner Programs Using LEX

Program Name

Write a Compiler Construction Program for Scanner Programs Using LEX.

Theory
Scanner Programs Using LEX

Program Code


%{
void display(char*,int);
%}
digit [0-9]
letter [A-Za-z]
number {digit}+
specialsymbol [,|;|""]
operator [+|\-|*|/]
identifier {letter}({letter}|{digit})*
signednumber [+|\-]?{number}
%%
auto|int|main|void display(yytext,1);
{identifier} display(yytext,2);
{operator} display(yytext,3);
{specialsymbol} display(yytext,4);
{signednumber} display(yytext,5);
%%
main(int argc,char* argv[])
{
yyin=fopen(argv[1],"r");
yylex();
fclose(yyin);
}
void display(char *yytext,int c)
{
switch(c)
{
case 1:printf("%s is a Keyword\n",yytext); 	break;
case 2:printf("%s is a Identifier\n",yytext); 	break;
case 3:printf("%s is a Operator\n",yytext);	break;
case 4:printf("%s is a Specialsymbol\n",yytext);break;
case 5:printf("%s is a Signednumber\n",yytext);break;
}
}
int yywrap(){	return 1;	}

Create a text file b.txt and enter data.
Vi b.txt
hello world
welcome
12 + 24
" "

Saving: vi scanner.l

Compiling and Running
lex ab.l
cc lex.yy.c
./a.out

Input
Vi b.txt
hello world
welcome
12 + 24
" "

Output
hello is a Identifier
world is a Identifier
welcome is a Identifier

12 is a Signednumber
+ is a Operator
24 is a Signednumber

" is a Specialsymbol
" is a Specialsymbol

Home Back