Can't compile flex & bison (Symbols not found x86_64)

问题

I am trying to compile a simple program on Flex & Bison on my Mac running Yosemite but get the following error:

Undefined symbols for architecture x86_64: "_yyerror", referenced from: _yyparse in pr1-19c182.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

My two files look like this, they compile on my teacher's Ubuntu installation but I can't get them to work on my Mac:

pr1.y

%{
    #include <stdio.h>
%}

%%

expr : expr '+' term {printf(" + ");}
    | term 
    ;

term : term '*' fact {printf(" * ");}
    | fact 
    ;

fact : "(" expr ")"
    | '0' {printf("0");}
    | '1' {printf("1");}
    | '2' {printf("2");}
    | '3' {printf("3");}
    | '4' {printf("4");}
    | '5' {printf("5");}
    | '6' {printf("6");}
    | '7' {printf("7");}
    | '8' {printf("8");}
    | '9' {printf("9");}

%%

pr1.l

%{
    #include "pr1.tab.h"
%}

%%

[0-9]   {return (yytext[0]);}
[+*()]  {return (yytext[0]);}
\n      {return (0);}
.       {}

%%

I compile everything using the following commands:

bison -d pr1.y
flex pr1.l
gcc -o result lex.yy.c pr1.tab.c -lfl -std=gnu89

The reason I use the -std flag is because the default is c99 and the code generated by flex and bison gets warnings and errors. Any ideas???

回答1:

You need to define yyerror in your bison input file (pr1.y). And you need to declare yylex or you will get another warning.

The following would be fine:

%{
   #include <stdio.h>
   void yyerror(const char* msg) {
      fprintf(stderr, "%s\n", msg);
   }
   int yylex();
%}

I have no idea how it works without that on your teacher's machine.

Also, Mac OS X has very old versions of bison and flex. You might want to upgrade.

回答2:

Check out the 2nd comment of the answer on this post Unable to compile output of lex

On Mac OS X, if you're trying to compile from the command line, you need to link against the libl.a library, by using -ll instead of -lfl. Apparently OS X has no libfl.a library. So try this...

gcc -o result lex.yy.c pr1.tab.c -ll

Don't know about your need for the -std=gnu89 option.

来源：https://stackoverflow.com/questions/28207339/cant-compile-flex-bison-symbols-not-found-x86-64

标签

macos

bison

osx-yosemite

flex-lexer