Undefined symbols for architecture x86_64:"_yylval", referenced from _yylex on Mac OS

Question

I'm trying out some examples from O'Reilly Flex & Bison. The first Bison and Flex program I'm trying gives me next error when linking the sources:

Undefined symbols for architecture x86_64: "_yylval", referenced

from:

  _yylex in lex-0qfK1M.o

As I'm new to Mac and I'm just trying the examples, I have no clue what's wrong here.

l file:

/* recognize tokens for the calculator and print them out */
%{
#include "fb1-5.tab.h"
%}

%%
"+"     { return ADD; }
"-"     { return SUB; }
"*"     { return MUL; }
"/"     { return DIV; }
"|"     { return ABS; }
[0-9]+  { yylval = atoi(yytext); return NUMBER; }
\n      { return EOL; }
[ \t]   { /* Ignore whitespace */ }
.       { printf("Mystery character %c\n", *yytext); }
%%

y file:

/* simplest version of calculator */
%{
#include <stdio.h>
%}
/* declare tokens */
%token NUMBER
%token ADD SUB MUL DIV ABS
%token EOL
%%
calclist: /* nothing */ matches at beginning of input
 | calclist exp EOL { printf("= %d\n", $1); } EOL is end of an expression
 ;
exp: factor default $$ = $1
 | exp ADD factor { $$ = $1 + $3; }
 | exp SUB factor { $$ = $1 - $3; }
 ;
factor: term default $$ = $1
 | factor MUL term { $$ = $1 * $3; }
 | factor DIV term { $$ = $1 / $3; }
 ;
term: NUMBER default $$ = $1
 | ABS term { $$ = $2 >= 0? $2 : - $2; }
 ;
%%
main(int argc, char **argv)
{
    yyparse();
}

yyerror(char *s)
{
    fprintf(stderr, "error: %s\n", s);
}

Command line:

bison -d fb1-5.y
flex fb1-5.l
cc -o $@ fb1-5.tab.c lex.yy.c -ll

I use -ll instead of -lfl because apparently on Mac os x, the fl library isn't there.

Output:

Undefined symbols for architecture x86_64:
  "_yylval", referenced from:
      _yylex in lex-0qfK1M.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Any ideas?

Fortuneteller

Your .y file is a copy of your .l file -- which will cause all kinds of errors from bison. yylval is defined in the code generated by bison... – Systematics

Ow, my bad, will edit the post. – Fortuneteller

I'll try this tonight #3299218 , maybe it solves the problem. – Fortuneteller

Answer 1

Apparently the Flex & Bison book from O'Reilly is full of errors.

See http://oreilly.com/catalog/errataunconfirmed.csp?isbn=9780596155988

Very weird that they do not even bother test their own examples...

Part of the question is solved in Undefined reference to yyparse (flex & bison) but not everything. See the errataunconfirmed page.

Fortuneteller

Answer 2

I caused a similar error by compiling a lex file that began

%{
#include "y.tab.h"
%}

using the command

gcc -ll lex.yy.c

This worked:

gcc -ll y.tab.c lex.yy.c

What's going on? There's a declaration in y.tab.h

extern int yylval

which allows lex.yy.c to compile. However, lex.yy.o needs to be linked against an object file that includes yylval, such as y.tab.o

Strontian

Thank you VERY much. This is so arcane and should be mentioned in the Lex and Yacc book I'm following. – Autum