Question

I’m trying to compile a simple calculator example that I found in the internet for my embedded environment, but I’m having a few difficulties regarding dependencies with flex/bison.

My test files are these:

lexer.l

%{
// lexer.l     From tcalc: a simple calculator program
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include "tcalc.tab.h"
extern YYSTYPE yylval;

%}
%option noyywrap
%option never-interactive
%option nounistd
delim         [ \t]
whitesp       {delim}+
digit         [0-9]
number        [-]?{digit}*[.]?{digit}+
%%
{number}  { sscanf(yytext, "%lf", &yylval); return NUMBER;}
"+"       { return PLUS; }
"-"       { return MINUS; }
"/"       { return SLASH; }
"*"       { return ASTERISK; }
"("       { return LPAREN; }
")"       { return RPAREN; }
"\n"      { return NEWLINE; }
{whitesp} { /* No action and no return */}

tcalc.y

/* tcalc.y - a four function calculator */
%{
#define YYSTYPE double      /* yyparse() stack type */
#include <stdlib.h>
%}
/* BISON Declarations */
%token NEWLINE NUMBER PLUS MINUS SLASH ASTERISK LPAREN RPAREN

/* Grammar follows */
%%
input:              /* empty string */
    | input line
    ;
line: NEWLINE
    | expr NEWLINE           { printf("\t%.10g\n",$1); }
    ;
expr: expr PLUS term         { $$ = $1 + $3; }
    | expr MINUS term        { $$ = $1 - $3; }
    | term
    ;
term: term ASTERISK factor   { $$ = $1 * $3; }
    | term SLASH factor      { $$ = $1 / $3; }
    | factor
    ;
factor:  LPAREN expr RPAREN  { $$ = $2; }
      | NUMBER
      ;
%%
/*--------------------------------------------------------*/
/* Additional C code */
/* Error processor for yyparse */
#include <stdio.h>
int yyerror(char *s)        /* called by yyparse on error */
{
    printf("%s\n",s);
    return(0);
}

/*--------------------------------------------------------*/
/* The controlling function */
#include "lex.h"
int parse(void)
{
    char exp[] = "2+3\n\0\0";
    yy_scan_buffer(exp, sizeof(exp));
    yyparse();
    exit(0);
}

When I try to compile it with my compiler, I get an error about EINTR not being found. There is no EINTR in my errno.h header (from my compiler’s toolchain).

Is there some options do make flex/bison more lightweight and depend less on POSIX stuff?

Answer 1

In short: No. flex will reference EINTR in all C scanners. So you basically have three choices (in descending order):

1. Fix your compiler. Which one doesn’t define EINTR?
2. Define your own YY_INPUT in a %top block.
3. Define a dummy EINTR; 0 or INT_MAX are probably good choices for this specific application but redefining standard macros can always have funny side-effects.