MinGW - Minimalist GNU for Windows

The following off-topic message was originally posted on MinGW-MSYS
I am transferring it to here, where it is on-topic...

On Thursday 22 January 2009 04:35:53 Sukhbir Singh wrote:
> While intergrating FFMpeg statis libs with my own code written in
> c++ using MSVC++ 6.0,
> i am getting following linking error:
> libmingwex.a(pformat.o) : error LNK2001: unresolved external symbol
> __get_output_format
>
> Please help me out.
> I will appreciate your efforts.

Yes, I can give an authoritative answer to this, but I will have to 
get back to you, probably early next week.  However, as the subject 
is completely unrelated to MSYS, I am transferring the discussion to 
MinGW-Users@..., which is where you should have 
asked this question in the first place, and is where you will find my 
authoritative answer, in due course.

In the meantime, you should visit:
https://lists.sourceforge.net/mailman/listinfo/mingw-users

and subscribe, to ensure that you are able to continue to participate 
in the discussion.

-- 

Regards,
Keith.

On Thursday 22 January 2009 17:02:42 Sukhbir Singh wrote:
> While intergrating FFMpeg static libs with my own code written in
> c++ using MSVC++ 6.0,

First, a plug for free software: had you chosen to build your entire 
application using MinGW, instead of using this outdated, proprietary, 
non-free and restrictively licensed compiler suite, then you would 
never have encountered...

> I am getting following linking error:
> libmingwex.a(pformat.o) : error LNK2001: unresolved external symbol
> __get_output_format

...this error.

Ok.  This probably isn't the answer you hoped for, so here is the 
authoritative answer I promised, when I responded to your earlier 
post to MinGW-MSYS.

  int _get_output_format( void );

is a standard MSVC function, but it was not introduced until VS-2005; 
therefore, there is no implementation provided by VC-6.0.  To support 
users of more recent MSVC, (with MSVCRT version >= 8.00), who might 
also wish to use the _set_output_format() feature, and who also wish 
to use MinGW's enhanced printf() implementation, (which is what uses 
pformat.o), a call to _get_output_format() is needed.  To satisfy 
that requirement, when linking against earlier MSVCRT versions, 
MinGW's own import libraries provide a stub implementation of this 
function, which isn't provided by Microsoft's own libraries.  Thus, 
you need to provide your own stub; add:

  int _get_output_format( void ){ return 0; }

as a global function definition, to the source which provides your 
main() function, when you must use non-MinGW libraries, for linking 
to MSVCRT versions predating msvcr80.dll.

-- 

Regards,
Keith.

Hi Keith,

 Thanks for you reply.
 I did everything that you have mentioned in your last mail.
 i have globaliy defined the _get_output_format function in my code.
 But still i am getting same linking error.
 About msvcr80.dll, i did not get you.
 Please help me out.

With Regards,
Sukhbir

On Fri, Jan 23, 2009 at 1:30 AM, Keith Marshall <
keithmarshall@...> wrote:

> On Thursday 22 January 2009 17:02:42 Sukhbir Singh wrote:
> > While intergrating FFMpeg static libs with my own code written in
> > c++ using MSVC++ 6.0,
>
> First, a plug for free software: had you chosen to build your entire
> application using MinGW, instead of using this outdated, proprietary,
> non-free and restrictively licensed compiler suite, then you would
> never have encountered...
>
> > I am getting following linking error:
> > libmingwex.a(pformat.o) : error LNK2001: unresolved external symbol
> > __get_output_format
>
> ...this error.
>
> Ok.  This probably isn't the answer you hoped for, so here is the
> authoritative answer I promised, when I responded to your earlier
> post to MinGW-MSYS.
>
>  int _get_output_format( void );
>
> is a standard MSVC function, but it was not introduced until VS-2005;
> therefore, there is no implementation provided by VC-6.0.  To support
> users of more recent MSVC, (with MSVCRT version >= 8.00), who might
> also wish to use the _set_output_format() feature, and who also wish
> to use MinGW's enhanced printf() implementation, (which is what uses
> pformat.o), a call to _get_output_format() is needed.  To satisfy
> that requirement, when linking against earlier MSVCRT versions,
> MinGW's own import libraries provide a stub implementation of this
> function, which isn't provided by Microsoft's own libraries.  Thus,
> you need to provide your own stub; add:
>
>  int _get_output_format( void ){ return 0; }
>
> as a global function definition, to the source which provides your
> main() function, when you must use non-MinGW libraries, for linking
> to MSVCRT versions predating msvcr80.dll.
>
> --
>
> Regards,
> Keith.
>
>
> ------------------------------------------------------------------------------
> This SF.net email is sponsored by:
> SourcForge Community
> SourceForge wants to tell your story.
> http://p.sf.net/sfu/sf-spreadtheword
> _______________________________________________
> MinGW-users mailing list
> MinGW-users@...
>
> You may change your MinGW Account Options or unsubscribe at:
> https://lists.sourceforge.net/lists/listinfo/mingw-users
>
> _______________________________________________
> This list observes the Etiquette found at
> http://www.mingw.org/Mailing_Lists.
> We ask that you be polite and do the same.
>

Hi Sukhbir,


>> On Thursday 22 January 2009 17:02:42 Sukhbir Singh wrote:
>> > While intergrating FFMpeg static libs with my own code written in
>> > c++ using MSVC++ 6.0,

Keith Marshall wrote:
>>  int _get_output_format( void ){ return 0; }
>>
>> as a global function definition, to the source which provides your
>> main() function, when you must use non-MinGW libraries, for linking
>> to MSVCRT versions predating msvcr80.dll.

Sukhbir Singh writes:
>  i have globaliy defined the _get_output_format function in my code.
>  But still i am getting same linking error.

You mention that you write C++.  In a C++ file that function would
need to have an 'extern "C"' added to make it compatible with C.  So
that would make:

  extern "C" int _get_output_format( void ){ return 0; }


benny

Thanks for your support

On Sat, Jan 24, 2009 at 10:19 PM, Benjamin Riefenstahl <
b.riefenstahl@...> wrote:

> Hi Sukhbir,
>
>
> >> On Thursday 22 January 2009 17:02:42 Sukhbir Singh wrote:
> >> > While intergrating FFMpeg static libs with my own code written in
> >> > c++ using MSVC++ 6.0,
>
> Keith Marshall wrote:
> >>  int _get_output_format( void ){ return 0; }
> >>
> >> as a global function definition, to the source which provides your
> >> main() function, when you must use non-MinGW libraries, for linking
> >> to MSVCRT versions predating msvcr80.dll.
>
> Sukhbir Singh writes:
> >  i have globaliy defined the _get_output_format function in my code.
> >  But still i am getting same linking error.
>
> You mention that you write C++.  In a C++ file that function would
> need to have an 'extern "C"' added to make it compatible with C.  So
> that would make:
>
>  extern "C" int _get_output_format( void ){ return 0; }
>
>
> benny
>
>
> ------------------------------------------------------------------------------
> This SF.net email is sponsored by:
> SourcForge Community
> SourceForge wants to tell your story.
> http://p.sf.net/sfu/sf-spreadtheword
> _______________________________________________
> MinGW-users mailing list
> MinGW-users@...
>
> You may change your MinGW Account Options or unsubscribe at:
> https://lists.sourceforge.net/lists/listinfo/mingw-users
>
> _______________________________________________
> This list observes the Etiquette found at
> http://www.mingw.org/Mailing_Lists.
> We ask that you be polite and do the same.
>
> Most annoying abuses are:
> 1) Top posting
> 2) HTML/MIME encoded mail
> 3) Improper quoting
> 4) Improper trimming
>

On Saturday 24 January 2009 16:49:55 Benjamin Riefenstahl wrote:
> Sukhbir Singh writes:
> >  i have globaliy defined the _get_output_format function in my
> > code. But still i am getting same linking error.
>
> You mention that you write C++.  In a C++ file that function would
> need to have an 'extern "C"' added to make it compatible with C.
>  So that would make:
>
>   extern "C" int _get_output_format( void ){ return 0; }

Indeed.  Thanks Benny; I overlooked that little wrinkle in my original 
reply, perhaps because I rarely write C++.

Another wrinkle: if you write it instead, as

  extern "C" int _get_output_format( void ){ return 1; }

you will get ISO C99 conformant 2-digit exponents, rather than the 
Microsoft non-conformist 3-digits, in the "%e" and "%g" formats, when 
your application calls any of the MinGW enhanced printf() functions.
(However, adding PRINTF_EXPONENT_DIGITS=2 to your environment remains 
the preferred way to achieve this).

-- 

Regards,
Keith.

On Friday 23 January 2009 15:08:42 Sukhbir Singh wrote:
>  About msvcr80.dll, i did not get you.
>  Please help me out.

msvcr80.dll is the version of Microsoft's C runtime library first 
published to accompany VS-2005, IIRC.  You will have an earlier 
version with your MSVC-6.0, and that version, compatible with the 
msvcrt.dll used as default by MinGW, lacks the _get_output_format() 
function, which first appeared in msvcr80.dll.

MinGW's enhanced printf() functions include support for the 2-digit 
exponent capability, also introduced in msvcr80.dll.  That means that 
our printf() functions need to call _get_output_format(), and to make 
that possible, even with the earlier MSVCRT versions, we add a stub 
to *our* import libraries for those older DLL versions.  Of course, 
Microsoft's implementations of those import libraries provide no 
such "forward compatibility" support.

Regards,
Keith.