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I'm trying to make a compiler for a mini Pascal-like language. I'm using Flex and Bison for this and I came up with this error.
My Flex file:
#include "y.tab.h"
#include <stdlib.h>
#include <string.h>
#include <math.h>
void yyerror(char *);
[1-9][0-9]* {
yylval.i = atoi(yytext);
return INT;
program return PROGRAM;
or return OR;
and return AND;
not return NOT;
if return IF;
else return ELSE ;
while return WHILE;
"+" return PLUS;
"-" return MINUS;
"*" return MUL;
"/" return DIV;
"[" return LSB;
"]" return RSB;
"{" return LCB;
"}" return RCB;
"(" return LEFTPAR;
")" return RIGHTPAR;
":=" return ASSIGN;
"==" return ISEQUAL;
"<" return LTHAN;
">" return GTHAN;
"<>" return NOTEQUAL;
"<=" return LESSEQUAL;
">=" return GREATEREQUAL;
[a-zA-z][a-z0-9]* {
yylval.s = (char*)malloc(strlen(yytext)*sizeof(char));
strcopy(yylval.s,yytext);
return ID;
[ \t\n]+ /* eat up whitespace */
. yyerror("Unknown Character");
int yywrap(void) {
return 1;
My Bison file:
#include <stdio.h>
#include <string.h>
int yylex(void);
void yyerror(char *s);
%union {
int i;
char *s;
%token <i> INTEGERNUM
%token PROGRAM;
%token OR;
%token AND;
%token NOT;
%token IF;
%token ELSE;
%token WHILE;
%token PLUS;
%token MINUS;
%token MUL;
%token DIV;
%token LSB;
%token RSB;
%token LCB;
%token RCB;
%token LEFTPAR;
%token RIGHTPAR;
%token ID;
%token INT;
%token ASSIGN;
%token ISEQUAL;
%token LTHAN;
%token GTHAN;
%token NOTEQUAL;
%token LESSEQUAL;
%token GREATEREQUAL;
program:
PROGRAM ID block
block:
LCB sequence RCB
sequence:
statement ';' sequence
| statement ';'
bracketsSeq:
LCB sequence RCB
brackOrStat:
bracketsSeq
| statement
statement:
assignmentStat
|ifStat
|whileStat
assignmentStat:
ID ':=' expression
ifStat:
IF LEFTPAR condition RIGHTPAR brackOrStat elsepart
elsepart:
ELSE brackOrStat
whileStat:
WHILE LEFTPAR condition RIGHTPAR brackOrStat
expression:
optionalSign expression
|expression addOper expression
|term
term:
term mulOper term
|factor
factor:
|LEFTPAR expression RIGHTPAR
condition:
condition AND condition
|boolterm
boolterm:
boolterm OR boolterm
|boolfactor
boolfactor:
NOT LSB condition RSB
|LSB condition RSB
|expression relationalOper expression
relationalOper:
ISEQUAL
|LTHAN
|GTHAN
|NOTEQUAL
|LESSEQUAL
|GREATEREQUAL
addOper:
|MINUS
mulOper:
optionalSign:
addOper
int main( int argc, char **argv )
printf("TEST\n");
The series of steps I executed was:
$ ./bison.exe -dy comp.y
$ ./flex.exe comp.l
$ gcc -c -w lex.yy.c
$ gcc -c -w comp.tab.c
$ gcc comp.tab.o lex.yy.o -o ex
comp.tab.o:comp.tab.c:(.text+0x4cd): undefined reference to `_yyerror'
comp.tab.o:comp.tab.c:(.text+0x61c): undefined reference to `_yyerror'
lex.yy.o:lex.yy.c:(.text+0x34a): undefined reference to `_strcopy'
lex.yy.o:lex.yy.c:(.text+0x362): undefined reference to `_yyerror'
/usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../../i686-pc-cygwin/bin/ld: lex.yy.o: bad reloc address 0x828 in section `.rdata'
/usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../../i686-pc-cygwin/bin/ld: final link failed: Invalid operation
collect2: ld returned 1 exit status
Any advice as to what to declare and where cause there seems to be that I have declared something the wrong way!
–
It's not enough to declare yyerror. You must provide a definition.
The bison manual suggests the following as a minimal implementation:
void yyerror (char const *s) {
fprintf (stderr, "%s\n", s);
The other problem you have is that you misspelled strcpy in your flex file.
More accurately, the other problem revealed by the linker errors is the misspelled strcpy, because your copying code is incorrect. It does not account for the NUL byte which must terminate strings. strcpy will copy that byte, with the result that it will write a 0 in unallocated storage. You'll find it much simpler to use strdup. (And don't forget that you need to free the strings when you're finished with them.)
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