CODEWITHSUNDEEP
flex-lexer
user2690798
user2690798

Reputation: 47

How can I make my FLEX program ignore special characters at certain times?

I am writing a simple tokenization program for a calculator program to come later. Right now I have the program coded to output 'FALSE' whenever 'f' is entered by the user. What I am currently working on is making it so when the user enters '//' followed by a string, the program outputs "COMMENT: // string I entered". Here is my issue: Because I have 'f' and other single characters programmed to do other things, my program currently creates this type of output:

**User enters:**

//Protoypes

**Desired Output:**

COMMENT: //Prototypes

**Actual Output:**

COMMENT: // Pro

TRUEo

TRUEypes

Does anyone have a way of fixing this?

Here's the code so far:

%{

#include <stdio.h>

%}

%%

"//"    printf("\nCOMMENT: // ", yytext);

"("     printf("\nLPAREN");

")"     printf("\nRPAREN");

"="     printf("\nASSIGN");

"F"     printf("\nFALSE");

"T"     printf("\nTRUE");

"and"   printf("\nAND");


"bye"   printf("\nQUIT");

"else"  printf("\nELSE");

"exit"  printf("\nQUIT");

"f"     printf("\nFALSE");

"false" printf("\nFALSE");

"if"    printf("\nIf");

"implies"       printf("\nIMPLIES");

\n      printf("\nNEWLINE");

"not"   printf("\nNOT");

"or"    printf("\nOR");

"quit"  printf("\nQUIT");

"stop"  printf("\nQUIT");

"t"     printf("\nTRUE");

"then"  printf("\nTHEN");

"true"  printf("\nTRUE");

"xor"   printf("\nXOR");


%%
main(){
    yylex();
}

Upvotes: 1

Views: 1581

Answers (1)

user207421
user207421

Reputation: 310903

You need a final rule that catches anything else and ignores it. The default is to print any unmatched input:

. ;

Upvotes: 1

Related Questions