linker error with hpp and cpp files added to a library
<p>I am using dev c++. also i am getting assistant from a library, developed by somebody else for my own c++ projects. i have added two new classes called <code>TriangleList</code> and <code>TriangleLists</code> to the library as i wanted new class types for the project. once, i added the hpp and cpp files to the library, i got the massage like <code>creating ../lib/libExtraction.a</code> . 
however, when i called back the functions, that i written in the new classes, from my own project, i got the error massages like </p>

<pre><code>`[Linker error] undefined reference to `TriangleLists::Erase()`
</code></pre>

<p>(the above one for the Erase function)
then, when i removed the .cpp file and wrote everything in .hpp it works.</p>

<p>But, i would like to maintain two files for the hpp and cpp further. so, please tell me how to solve this link error problem as i want to learn this. thank you in advance.</p>
