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Re: Adding configure flag

First of all, thank you so much for the quick reply! I still have some
questions if you don't mind! :)

On Wed, Oct 21, 2015 at 5:25 PM, Jonathan Wakely <> wrote:
> On 21 October 2015 at 20:37, Aurelio Remonda wrote:
>> Hi, im trying to add a configure flag to the libstdc++ for a feature
>> I'm testing. This flag, if enabled, would define a C macro that I'd be
>> using in
>> I was doing some research and i believe i need to edit
>> and acinclude.m4 on the libstdc++-v3 directory. Is this correct?
>> I also need to run autoconf to regenerate the libstdc++-v3 configure
>> script, right?
> Yes. I use autoreconf to ensure all relevant files are regenerated
> (using autoreconf doesn't work for all of GCC, but it does for
> libstdc++).
>> Do i need to make changes on the file in the top gcc
>> directory? Or can i create the flag and do the configure and make on
>> the libstdc++-v3 directory so it's ready for when I compile all of
>> gcc?
> Just in libstdc++-v3

Ok but, that means that i will have to do configure and make on libstdc++
and then compile gcc? or just make the changes, the autoreconf and then
when i compile gcc the libstdc++ will be compiled with my changes?

>> On a related subject: right now, I've added the following line to the
>> libstdc++v3's
>> Also, I added the following to libstdc++v3's acinclude.m4:
>>   GLIBCXX_ENABLE(new-opnt-if,$1,,[enable if on new_opnt instead of while])
>>   if test $enable_new_opnt_if = yes; then
>>         [Define is new_opnt will be used instead of while.])
>>   fi
>>   AC_MSG_CHECKING([for enabled if])
> This message isn't very helpful.

This is just a test, the message is just for me for now.

>>   AC_MSG_RESULT([$enable_new_opnt_if])
>> ])
>> And on gcc top directory
>> [AS_HELP_STRING([--enable-new-opnt-if],
>>     [enable if on new_opnt instead of while])],
>> [], [enable_new_opnt_if=yes])
>> AC_SUBST(enable_multilib)
> That shouldn't be there.
> That description of the option is useless to end users anyway. Instead
> it should be documented in libstdc++-v3/doc/xml/manual/configure.xml
>> As you can see, I've hardcoded this option as "yes" to test it.
>> However, I can't seem to make it work: in, I still can't
>> see the macro defined. Am I doing something wrong?
> It looks like you've hardcoded it to no, in libstdc++-v3/
> Try using autoreconf, to make sure is regenerated
> (although I think autoconf should do that anyway).
> Try either changing the default in libstdc++-v3/ or using
> --enable-new-opnt-if explicitly.

I did try it with --enable-new-opnt-if when i configure gcc, that should replace
the harcored "no" right?

> I hope if you're planning to propose this for inclusion in upstream
> GCC you'll give the option a more descriptive name.

Aurelio Remonda

Software Engineer

San Lorenzo 47, 3rd Floor, Office 5
CÃrdoba, Argentina
Phone: +54-351-4217888 / 4218211

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