Import error:undefined symbol

Hi all,

I want to make a simple hard limiter block (hlimit_ff()) which works as
follows:

if input<0
output=-1
else if input>0
output=1
else
output=0

So, in essence, I have downloaded the tar ball
gr-how-to-write-a-block-3.2.tar.gz and replaced ‘square’ with ‘hlimit’
in the howto_square_ff.h, howto_square_ff.cc and modified the general
work method (as above) in the howto_square_ff.cc and modified the
makefile.am and howto.i in /src/lib appropriately. Also, I have modified
the qa_howto.py in scr/python to run the test for hardlimit block. But I
get the following error when I run make check:

Traceback (most recent call last):
File “./qa_howto.py”, line 24, in
import howto
File “/home/mahboob/Desktop/howto/src/lib/howto.py”, line 24, in

_howto = swig_import_helper()
File “/home/mahboob/Desktop/howto/src/lib/howto.py”, line 16, in
swig_import_helper
import _howto
ImportError: /home/mahboob/Desktop/howto/src/lib/.libs/_howto.so:
undefined symbol: _Z23howto_make_hardlimit_ffv
FAIL: run_tests

1 of 1 test failed

Can any one please point out the mistake please?

Thanks,
Mahboob

p.s. I have checked and tried almost all options from the mailing list
archive.