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ccompiler-constructionflex-lexer

Why the below flex code doesn't show output?

digit  [0-9]
letter [A-Za-z]
%{
int count;
%}
%%
     /* match identifier */
{letter}({letter}|{digit})*  count++;
%%
int main(void) {
yylex();
printf("number of identifiers = %d\n", count);
return 0;
}

Doesn't work printf statement. can you explain what should i include in this code.

Solution

  • If you have an error with yywrap -- just add %option noyywrap:

    digit  [0-9]
letter [A-Za-z]
%{
    int count;
%}

%option noyywrap

%%
     /* match identifier */
{letter}({letter}|{digit})*  count++;
%%

int main(void) {
    yylex();
    printf("number of identifiers = %d\n", count);
    return 0;
}

    Then compile:

    flex f.l
gcc lex.yy.c

    Run and don't forget to send EOF at the end (with Ctrl-D):

    ./a.out
a a a

number of identifiers = 3