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

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

Do you have the flex source to hand? There's several c++ examples in the test suite that might be helpful to you. The manual should also have working examples. (I.e. if it doesn't, or if you do what they do and still see the same problem, that's a bug.)

On Wednesday,  8 October 2014,  3:25 pm +0400, "Filipp B." <b_...@zo...> wrote:

> Which header is that? I tried to include FlexLexer.h but then the
> compiler says that I am trying to redefine class.
> 
> 
> On 08.10.2014 15:03, Will Estes wrote:
> > 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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> 
> -- 
> Filipp B.
> 
> 
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