为什么下面的flex代码不显示输出？

Question

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.

Answer 1

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