I'm attempting to learn some flex/bison, and I'm reading Flex & Bison by John Levine (O'Reilly). There is an example that I need to get running, however I can't get it to run as I get the following error:
/tmp/ccKZcRYB.o: In function `yylex': fb3-1.lex.c:(.text+0x2bd): undefined reference to `yylval' /tmp/cclBqnOk.o: In function `main': fb3-1funcs.c:(.text+0x420): undefined reference to `yyparse' collect2: ld returned 1 exit status I've got four source files:
fb3-1.h:
/* * Declarations for calculator fb3-1 */ /* Interface to the lexer */ extern int yylineno; /* from lexer */ void yyerror(char *s, ...); /* nodes in the abstract syntax tree */ struct ast { int nodetype; struct ast *l; struct ast *r; }; struct numval { int nodetype; /* type K for constant */ double number; }; /* build an AST */ struct ast *newast(int nodetype, struct ast *l, struct ast *r); struct ast *newnum(double d); /* evaluate an AST */ double eval(struct ast *); /* delete and free an AST */ void treefree(struct ast *); fb3-1.l
/* recognise tokens for the calculator */ %option noyywrap nodefault yylineno %{ #include "fb3-1.h" #include "fb3-1.tab.h" %} /* float exponent */ EXP ([Ee][-+]?[0-9]+) %% "+" | "-" | "*" | "/" | "|" | "(" | ")" { return yytext[0]; } [0-9]+"."[0-9]*{EXP}? | "."?[0-9]+{EXP}? { yylval.d = atof(yytext); return NUMBER; } \n { return EOL; } "//".* [ \t] { /* ignore whitespace */ } . { yyerror("Mystery character %c\n", *yytext); } %% fb3-1.y
/* calculator with AST */ %{ #include <stdio.h> #include <stdlib.h> #include "fb3-1.h" %} %union { struct ast *a; double d; } /* declare tokens */ %token <d> NUMBER %token EOL %type <a> exp factor term %% calclist: /* nothing */ | calclist exp EOL { printf("=%4.4g\n",eval($2)); treefree($2); printf("> "); } | calclist EOL { printf("> "); } /* blank line or a comment */ ; exp: factor | exp '+' factor { $$ = newast('+', $1, $3); } | exp '-' factor { $$ = newast('-', $1, $3); } ; factor: term | factor '*' term { $$ = newast('*', $1, $3); } | factor '/' term { $$ = newast('/', $1, $3); } ; term: NUMBER { $$ = newnum($1); } | '|' term { $$ = newast('|', $2, NULL); } | '(' term { $$ = $2; } | '-' term { $$ = newast('M', $2, NULL); } ; %% fb3-1funcs.c
#include <stdio.h> #include <stdlib.h> #include <stdarg.h> #include "fb3-1.h" struct ast * newast(int nodetype, struct ast *l, struct ast *r) { struct ast *a = malloc(sizeof(struct ast)); if(!a) { yyerror("out of space"); exit(0); } a->nodetype = nodetype; a->l = l; a->r = r; return a; } struct ast * newnum(double d) { struct numval *a = malloc(sizeof(struct numval)); if(!a) { yyerror("out of space"); exit(0); } a->nodetype = 'K'; a->number = d; return (struct ast *)a; } double eval (struct ast *a) { double v; switch(a->nodetype) { case 'K': v = ((struct numval *)a)->number; break; case '+': v = eval(a->l) + eval(a->r); break; case '-': v = eval(a->l) + eval(a->r); break; case '*': v = eval(a->l) + eval(a->r); break; case '/': v = eval(a->l) + eval(a->r); break; case '|': v = eval(a->l); if(v < 0) v = -v; break; case 'M': v = -eval(a->l); break; default: printf("internal error: bad node %c\n", a->nodetype); } } void treefree(struct ast *a) { switch(a->nodetype) { /* two subtrees */ case '+': case '-': case '*': case '/': treefree(a->r); /* one subtree */ case '|': case 'M': treefree(a->l); /* no subtree */ case 'K': free(a); break; default: printf("internal error: free bad node %c\n", a->nodetype); } } void yyerror(char *s, ...) { va_list ap; va_start(ap, s); fprintf(stderr, "%d: error: ", yylineno); vfprintf(stderr, s, ap); fprintf(stderr, "\n"); } int main () { printf("> "); return yyparse(); } To Build:
bison -d fb3-1.y flex -ofb3-1.lex.c fb3-1.l cc -o $@ fb3-1.tab.c fb3-1.lex.c fb3-1funcs.c I'm running Ubuntu 10.04 x64, with the packages 'flex' and 'bison' installed. Anyone know why this error is happening, and how to fix it? Thanks in advance :)