# Question on how to derive a class in an out-of-tree module based on a gnuradio class **URL:** \ **Category:** GNU Radio\ **Created:** [October 7, 2014, 3:59am UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388 "2014-10-07T03:59:50Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [October 7, 2014, 3:59am UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/1 "2014-10-07T03:59:50Z")
Dear all, I’m trying to derive a _packet\_header2_ class in my own OOT module based on _gr::digital::packet\_header\_default_. I followed the way in _packet\_heade\_ofdm_ of gr-digital and made packet\_header2.h and packet\_header2.cc in my own OOT module. But when I tried to import my\_oot in python, it returned an undefined symbol error like this: Traceback (most recent call last): File “”, line 1, in File “/usr/local/lib/python2.7/dist-packages/my\_oot/ **init**.py”, line 45, in from my\_oot\_swig import \* File “/usr/local/lib/python2.7/dist-packages/my\_oot/my\_oot\_cdma.py”, line 26, in \_my\_oot\_swig = swig\_import\_helper() File “/usr/local/lib/python2.7/dist-packages/cdma/cdma\_swig.py”, line 22, in swig\_import\_helper \_mod = imp.load\_module(‘\_my\_oot\_swig’, fp, pathname, description) ImportError: /usr/local/lib/libgnuradio-my\_oot.so: undefined symbol: \_ZTIN2gr7digital21packet\_header\_defaultE I searched the list and found a previous answered question below [http://gnuradio.4.n7.nabble.com/so-undefined-symbol-ZN2gr6blocks12count-bits16E-td46270.html](http://gnuradio.4.n7.nabble.com/so-undefined-symbol-ZN2gr6blocks12count-bits16E-td46270.html) where Marcus suggested editing the CMakeList.txt files by adding the module I needed. So I added _set(GR\_REQUIRED\_COMPONENTS RUNTIME DIGITAL)_ in CMakeLists.txt. and then. This above error disappeared when I import my\_oot again in python. But this problem isn’t solved. I tried to access some functions of packet\_header\_default like formatter and base, it returned me an AtrributeError like this: AttributeError: ‘packet\_header2\_sptr’ object has no attribute ‘formatter’, which means the packet\_header2 wasn’t really a derived class of packet\_header\_default. I confirmed my conjecture by checking the /usr/local/lib/python2.7/dist-packages/my\_oot/my\_oot\_swig.py where the classes are stored in python. I found that the class packet\_header2 is defined as _class packet\_header2(object)_. So the packet\_header2 _isn’t_ installed as a derived class of _gr::digital::packet\_header\_default_. what I expected was _packet\_header2(gr::digital::packet\_header\_default)_. So I’m asking you that how to correctly derive my class (eg: packet\_header2) in my own oot module based on a class (eg: packet\_header\_default) in an existing module (eg: gr-digital)? My packet\_header2.h and packet\_header2.cc are attached for your reference. Thanks! Best, Zhe – Zhe F. Electrical Engineering: System University of Michigan Ann Arbor ---
**Author:** ![Zhe\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d07c76/32.png) [@Zhe\_F](https://www.ruby-forum.com/u/Zhe_F)\ **Post date:** [October 7, 2014, 9:55am UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/2 "2014-10-07T09:55:32Z")
This looks like a linker error. In your main CMakeList.txt, you have to add DIGITAL to the line containing set(GR\_REQUIRED\_COMPONENTS … If you already have that, sometimes make clean helps, when for some reason linker/ccache/black magic involving CMake failed. Greetings, Marcus ---
**Author:** ![Zhe\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d07c76/32.png) [@Zhe\_F](https://www.ruby-forum.com/u/Zhe_F)\ **Post date:** [October 7, 2014, 11:17am UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/3 "2014-10-07T11:17:53Z")
On 10/07/2014 09:54 AM, Marcus M. wrote: > This looks like a linker error. > In your main CMakeList.txt, you have to add DIGITAL to the line containing > > set(GR\_REQUIRED\_COMPONENTS … The OP mentioned he’d already done that, but I still agree with your suspicion. It’s actually more likely some SWIG/linking issue. Are you referencing the correct header files in your SWIG file? M ---
**Author:** ![Zhe\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d07c76/32.png) [@Zhe\_F](https://www.ruby-forum.com/u/Zhe_F)\ **Post date:** [October 7, 2014, 11:28am UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/4 "2014-10-07T11:28:59Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 … I should pay closer attention; sorry! On 07.10.2014 11:16, Martin B. wrote: > > On 07.10.2014 03:58, Zhe F. wrote: > > > > > Traceback (most recent call last): File “”, line 1, in > > > > > > I searched the list and found a previous answered question > > > below [http://gnuradio.4.n7.nabble.com/so-undefined-symbol-ZN2gr6blocks12count-bits16E-td46270.html](http://gnuradio.4.n7.nabble.com/so-undefined-symbol-ZN2gr6blocks12count-bits16E-td46270.html) > > > where Marcus suggested editing the CMakeList.txt files by adding the module > > > AttributeError: ‘packet\_header2\_sptr’ object has no attribute > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Discuss-gnuradio > mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJUM7IEAAoJEAFxB7BbsDrLiX8H/3gPnytHZ8+TLDJb4zWSj2yR mn8do7lA7QmuKU5sPq9xUbUyvaN+HhzJFiap1wYop/N7rVP5VESzPFoLrcci23RR /zfjy+pMyHw4WudpjpBVB0laSwQR6+SjyiKZEl0O/wlWxoTWSGOx5Q18YfOdW/i5 xWWTn9XDU5gmNnPNZElowyIEyG6yy7rpha8lIjzdaV6V5kPdNcw8nopOx4P5gb+z eUUAF0Z/3UCq5Og7u95hHA2F17hhh1aVy2yTYMU3JA/KpcUq/qk58K50AbS/Ycaw miFV5hKpMne/AxIPnEIlL2EVwpirGIjgTAbk6vbMfmIz0I5QBPeZDA6fYF4Bk70= =pGV9 -----END PGP SIGNATURE----- ---
**Author:** ![Zhe\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d07c76/32.png) [@Zhe\_F](https://www.ruby-forum.com/u/Zhe_F)\ **Post date:** [October 7, 2014, 12:40pm UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/5 "2014-10-07T12:40:49Z")
On 07 Oct 2014, at 12:02, Bastian B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I did that in gr-ieee802-11 and IIRC I had to define GR\_API in the swig config arg, sorry! I had to #define DIGITAL\_API and include packet\_header\_default.h > [https://github.com/bastibl/gr-ieee802-11/blob/master/swig/ieee802\_11\_swig.i#L18](https://github.com/bastibl/gr-ieee802-11/blob/master/swig/ieee802_11_swig.i#L18) I think that I also had some problems with the swig bindings without those includes and defines. ---
**Author:** ![Zhe\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d07c76/32.png) [@Zhe\_F](https://www.ruby-forum.com/u/Zhe_F)\ **Post date:** [October 7, 2014, 12:04pm UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/6 "2014-10-07T12:04:02Z")
Hi, I did that in gr-ieee802-11 and IIRC I had to define GR\_API in the swig config [https://github.com/bastibl/gr-ieee802-11/blob/master/swig/ieee802\_11\_swig.i#L18](https://github.com/bastibl/gr-ieee802-11/blob/master/swig/ieee802_11_swig.i#L18) Hope that helps, Bastian On 07 Oct 2014, at 11:27, Marcus M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > set(GR\_REQUIRED\_COMPONENTS … > > > > > > followed the way in _packet\_heade\_ofdm_ of gr-digital and made > > > > line 26, in \_my\_oot\_swig = swig\_import\_helper() File > > > > > > > > and base, it returned me an AtrributeError like this: > > > > _gr::digital::packet\_header\_default_. what I expected was – Dipl.-Inform. Bastian B. Distributed Embedded Systems Group University of Paderborn, Germany > **[Home](https://www.bastibl.net/)** > > I'm Bastian Bloessl, a Research Group Leader at the Secure Mobile Networking Lab, TU Darmstadt. Checkout my blog, projects, publications, and resume; or connect on Github, Twitter, YouTube, or Facebook. ---
**Author:** ![Zhe\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d07c76/32.png) [@Zhe\_F](https://www.ruby-forum.com/u/Zhe_F)\ **Post date:** [October 7, 2014, 2:20pm UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/7 "2014-10-07T14:20:08Z")
Hi Marcus, Martin and Bastian, Thanks for your help! You are right, it’s a linker error, the reason is absolutely what Martin mentioned that I didn’t refer the header files I used i.e packet\_header\_default.h in my swig file. I checked Bastian’s swig file and made this class working as expected! Thanks again! Best, Zhe On Tue, Oct 7, 2014 at 6:39 AM, Bastian B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > – Zhe F. Electrical Engineering: System University of Michigan Ann Arbor Tel: 734-834-3188 ---
**Author:** ![Zhe\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/d07c76/32.png) [@Zhe\_F](https://www.ruby-forum.com/u/Zhe_F)\ **Post date:** [October 12, 2014, 4:34pm UTC](https://www.ruby-forum.com/t/question-on-how-to-derive-a-class-in-an-out-of-tree-module-based-on-a-gnuradio-class/232388/8 "2014-10-12T16:34:52Z")
Zhe, every single developer who has ever written for GnuRadio runs into this particular swig necessity and searches like mad, certain it is done… Congrats.