Also add the estlib.lib need to be added to your .mmp file.
But this alone is not enough. You have to provide proper include path.
In my case, i was able to port my C type application which was using C type string processing. I also retained some of the C type file processing. You have to be careful in file handling. I ended up writing fwrite etc the symbian way. But this is not much and is a one time task.
Here is what i added to my myproj.mmp.
( Lib and header include i used.)