How to configure pkgconfig

[lxlenovostar]

I stuck on:

Traceback (most recent call last):
  File "example.py", line 3, in <module>
    import pyrtcdc
ImportError: ../src/librtcdc.so: undefined symbol: nice_candidate_free

I have read #19 .
But I‘m confused with this explanation:

$ PKG_CONFIG_PATH=/usr/local/opt/openssl/lib/pkgconfig:/usr/local/opt/libnice/lib/pkgconfig pkg-config --cflags openssl nice
-D_REENTRANT -I/usr/local/Cellar/openssl/1.0.2j/include -I/usr/local/opt/libnice/include/nice -I/usr/local/opt/libnice/0.1.13/include -I/usr/local/Cellar/glib/2.48.2/include/glib-2.0 -I/usr/local/Cellar/glib/2.48.2/lib/glib-2.0/include -I/usr/local/opt/gettext/include -I/usr/local/Cellar/pcre/8.39/include
$ PKG_CONFIG_PATH=/usr/local/opt/openssl/lib/pkgconfig:/usr/local/opt/libnice/lib/pkgconfig pkg-config --libs openssl nice
-L/usr/local/Cellar/openssl/1.0.2j/lib -L/usr/local/opt/libnice/lib -L/usr/local/Cellar/glib/2.48.2/lib -L/usr/local/opt/gettext/lib -lssl -lcrypto -lnice -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lintl 

Please explain how to configure pkgconfig.
Thank you.

[lxlenovostar]

I build librtcdc on Ubuntu 16.04 .
I install libnice, usrstcp, openssl in /opt, and I configure it by:
step1

#update /etc/ld.so.conf and add :
/opt
#execute the following command in the terminal
sudo ldconfig

step 2

cd librtcdc/src
#update Makefile: 
$(CC) -shared -fPIC $(LDFLAGS) $(OBJECTS) -o $@
#to:
$(CC) -shared -fPIC $(OBJECTS) $(LDFLAGS)-o $@

step 3

PKG_CONFIG_PATH=/opt/lib/pkgconfig pkg-config --cflags  openssl  nice 
PKG_CONFIG_PATH=/opt/lib/pkgconfig pkg-config --libs   openssl  nice
PKG_CONFIG_PATH=/opt/lib/pkgconfig   CPATH=/opt/include LIBRARY_PATH=/opt/lib  LD_LIBRARY_PATH=/opt/lib make

This work for me.