Writing re-entrant lexer with Flex

Question

I'm newbie to flex. I'm trying to write a simple re-entrant lexer/scanner with flex. The lexer definition goes below. I get stuck with compilation errors as shown below (yyg issue):

reentrant.l:

/* Definitions */

digit           [0-9]
letter          [a-zA-Z]
alphanum        [a-zA-Z0-9]
identifier      [a-zA-Z_][a-zA-Z0-9_]+
integer         [0-9]+
natural         [0-9]*[1-9][0-9]*
decimal         ([0-9]+\.|\.[0-9]+|[0-9]+\.[0-9]+)

%{
    #include <stdio.h>

    #define ECHO fwrite(yytext, yyleng, 1, yyout)

    int totalNums = 0;
%}

%option reentrant
%option prefix="simpleit_"

%%

^(.*)\r?\n     printf("%d\t%s", yylineno++, yytext);

%%
/* Routines */

int yywrap(yyscan_t yyscanner)
{
    return 1;
}

int main(int argc, char* argv[])
{
    yyscan_t yyscanner;

    if(argc < 2) {
        printf("Usage: %s fileName\n", argv[0]);
        return -1;
    }

    yyin = fopen(argv[1], "rb");

    yylex(yyscanner);

    return 0;
}

Compilation errors:

vietlq@mylappie:~/Desktop/parsers/reentrant$ gcc lex.simpleit_.c 
reentrant.l: In function ‘main’:
reentrant.l:44: error: ‘yyg’ undeclared (first use in this function)
reentrant.l:44: error: (Each undeclared identifier is reported only once
reentrant.l:44: error: for each function it appears in.)

Answer 1

Problem solved! Just need to initialize the yyscanner and yyg as shown below:

/* Definitions */

digit           [0-9]
letter          [a-zA-Z]
alphanum        [a-zA-Z0-9]
identifier      [a-zA-Z_][a-zA-Z0-9_]+
integer         [0-9]+
natural         [0-9]*[1-9][0-9]*
decimal         ([0-9]+\.|\.[0-9]+|[0-9]+\.[0-9]+)

%{
    #include <stdio.h>

    #define ECHO fwrite(yytext, yyleng, 1, yyout)

    int totalNums = 0;
%}

%option reentrant
%option prefix="simpleit_"

%%

^(.*)\r?\n     printf("%d\t%s", yylineno++, yytext);

%%
/* Routines */

int yywrap(yyscan_t yyscanner)
{
    return 1;
}

int main(int argc, char* argv[])
{
    yyscan_t yyscanner;
    struct yyguts_t * yyg;

    yylex_init(&yyscanner);
    yyg = (struct yyguts_t*)yyscanner;

    if(argc < 2) {
        printf("Usage: %s fileName\n", argv[0]);
        return -1;
    }

    yyin = fopen(argv[1], "rb");

    yylex(yyscanner);

    yylex_destroy(yyscanner);

    return 0;
}