Re: [Flex-help] undefined reference to `yylex' when compiling as C++

[Will E. <wes...@gm...>]

Looks like you need to include the flex c++ header so that you have a c++ lexer function, if I'm reading your example right.

On Wednesday,  8 October 2014,  9:23 am +0400, "Filipp B." <b_...@zo...> wrote:

> Hello. I am just starting with flex and trying to compile a simple
> program, no bison yet.
> 
> /* calc.l */
> 
> %{
> #include <iostream>
> #include <exception>
> %}
> 
> %option debug
> %option nodefault
> %option noyywrap
> %option c++
> 
> %%
> \+          {
>                 std::cout << "PLUS" << std::endl;
>             }
> 
> \*          {
>                 std::cout << "MULTIPLY" << std::endl;
>             }
> 
> -           {
>                 std::cout << "MINUS" << std::endl;
>             }
> 
> \/          {
>                 std::cout << "DIVIDE" << std::endl;
>             }
> 
> .|\n        {
>                 std::terminate();
>             }
> %%
> 
> /* calc.l end */
> 
> The problem is the following:
> 
> $ flex calc.l && g++ lex.yy.cc -lfl
> /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/../../../../lib64/libfl.a(libmain.o):
> In function `main':
> libmain.c:(.text.startup+0xb): undefined reference to `yylex'
> collect2: error: ld returned 1 exit status
> 
> 
> Writing pure C code using printf instead, with no %option c++, and
> compiling it with gcc works fine, but this doesn't. Why?
> 
> -- 
> Filipp B.
> 
> 
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