Error "undefined reference to..."

[almeria_new]

Hi!
The first thing to appear and thank you for the help that offers individuals like me
I have used google looking for this mistake and the majority of times appears on having wanted to compile some unload or to install some program and is commented that it is a thing of the gcc.
I am trying to realize an application that uses together files of code C and C ++. The files of C I them can modify to my broad ones, but they of C ++ are used by some libraries and functions that have prohibited me to modify.
This mistake me turns out to be always related to the calls that are done from the Class of C ++ to methods of C. If it does not matter for you, I put the exit of console:

host:~/Desktop/gop1 # make
gcc -c -I/usr/cxsc/include new_lst1_ari.cpp
gcc -c -I/usr/cxsc/include new_gop1.cpp
gcc new_lst1_ari.o new_gop1.o avl.o gop1_ex.cpp -o salida -I/usr/cxsc/include -L/usr/cxsc/lib -lcxsc
new_lst1_ari.o: In function `ArbolToVector(_nodo*, cxsc::ivector&, cxsc::intvector&)':
new_lst1_ari.cpp:(.text+0x5f7): undefined reference to `NumeroNodos(_nodo*, int*)'
new_gop1.o: In function `GlobalOptimize(DerivType (*)(DerivType const&), cxsc::interval, cxsc::real, _nodo*&, int&, cxsc::interval&)':
new_gop1.cpp:(.text+0x3ca): undefined reference to `NumeroNodos(_nodo*, int*)'
new_gop1.cpp:(.text+0x1515): undefined reference to `Insertar(_nodo**, double, double, double)'
new_gop1.cpp:(.text+0x1649): undefined reference to `Podar(_nodo**)'
new_gop1.cpp:(.text+0x16eb): undefined reference to `Insertar(_nodo**, double, double, double)'
new_gop1.o: In function `New_AllGOp1(DerivType (*)(DerivType const&), cxsc::interval, cxsc::real, cxsc::ivector&, cxsc::intvector&, int&, cxsc::interval&, int&, int)':
new_gop1.cpp:(.text+0x1b1b): undefined reference to `Podar(_nodo**)' collect2: ld returned 1 exit status

I have put in boldface the methods of C that are called from the class of C ++. And that I believe that they give the mentioned mistake.
If you need some information more at all mas to ask for it.
Thank you!!!

[almeria_new]

#include <cstdio>
extern "C" {
#include "avl.h"
}

I find it in this web:
[32] How to mix C and C++, C++ FAQ Lite