Xu Wang Xu Wang - 3 months ago 15
C++ Question

undefined reference to `yylex' && undefined reference to `yyin'

I'm trying to use flex and bison to create a compiler. But i receive errors when i try to compile.

Here is the errors:

flex --header-file=lex.h --outfile=lex.cc lex.ll
g++ -w -Wall -Wextra -ansi -g -c -o lex.o lex.cc -lm -ll
bison -v --output-file=parse.cc --defines=parse.hh --warnings=all --feature=all parse.yy
g++ -w -Wall -Wextra -ansi -g -c -o parse.o parse.cc
g++ -w -Wall -Wextra -ansi -g -c -o main.o main.cc
g++ -w -Wall -Wextra -ansi -g -fkeep-inline-functions -o LFIO lex.o parse.o function.o main.o -lfl -lm -ll
parse.o: In function `yyparse()':
/root/LFIO-combine/parse.cc:1199: undefined reference to `yylex'
main.o: In function `main':
/root/LFIO-combine/main.cc:21: undefined reference to `yyin'
/root/LFIO-combine/main.cc:21: undefined reference to `yyin'
collect2: error: ld returned 1 exit status
make: *** [LFIO] Error 1


Here is my makefile:

CXXFLAGS = -w -Wall -Wextra -ansi -g
OBJECTS = lex.o parse.o function.o main.o


LFIO : $(OBJECTS)
g++ $(CXXFLAGS) -fkeep-inline-functions -o LFIO $(OBJECTS) -lfl -lm -ll

clean :
rm -f *.o

lex.cc : lex.ll
flex --header-file=lex.h --outfile=lex.cc lex.ll

parse.hh : parse.cc

parse.cc : parse.yy function.h algorithm.h
bison -v --output-file=parse.cc --defines=parse.hh --warnings=all --feature=all parse.yy

%.o: %.cc %.h
g++ $(CXXFLAGS) -c -o $@ $< -lm -ll

main.o : main.cc lex.h parse.hh function.h algorithm.h

function.o : function.h function.cc

parse.o : parse.cc parse.hh function.h algorithm.h

lex.o :lex.h algorithm.h function.h


Here is my lex.ll

%option c++
%option ecs
%option nodefault
%option stack
%option warn
%option yylineno

%{
#include "function.h"
#include "parse.hh"
#include <limits.h>
#include <iostream>
#include <sstream>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
int yyFlexLexer::yywrap() { return 1; }
%}

ATOM [A-Z][a-zA-Z0-9_']*
VARIABLE [a-z][a-zA-Z0-9_']*

%%
[ \t\n] ;
{VARIABLE} { return (TOK_VARIABLE);}
{ATOM} { return (TOK_ATOM);}
":-" {}
"," {}
"." {}
<<EOF>> {yyterminate();}
%%


parse.yy is like this:

%defines
%define api.token.prefix {TOK_}

%{
#include "function.h"
#include "lex.h"
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#ifdef MS_WINDOWS
#include <malloc.h>
#define alloca_alloca
#endif
void yyerror(const char *s)
{
fprintf (stderr, "%s\n", s);
}
extern "C" int yylex(void);

%}

%union{
......
}

%type ......


%%
......


And then main.cc is like this:

#include "function.h"
#include "algorithm.h"
#include "parse.hh"
#include "lex.h"
extern "C" int yylex(void);
extern FILE *yyin;
extern FILE *yyout;
extern int fopen();
extern int yyparse(void *);

int main(int argc, char **argv){

if(argc > 1){
if(!(yyin = fopen(argv[1], "r"))) {
perror(argv[1]);
return (1);
}
}
//yylex();
yyparse();
......
return 0;
}


Does anybody know what cause these errors and how to solve them?
I would be thankful if someone could make time to check these errors.

Answer

Collecting my comments into an answer.

There are two problems:

The first is that the code is compiled as C++, which means the definition of yylex will also be compiled as C++. That means it is not extern "C". To fix this problem remove the extern "C" from all declarations.

The second problem is two-fold: The first is that the symbol yyin doesn't seem to be defined anywhere, so you need to do it yourself. The second thing is that it should be a pointer to an std::istream object, and not a FILE *.

To solve the second problem, with yyin, I recommend you add the definition to your lexer declaration block:

%{
// Your includes...
int yyFlexLexer::yywrap() { return 1; }

// Add definition of yyin
std::istream* yyin;
%}

Then update the extern declaration in your main.cc file to match the definition.

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