Why is mex displaying irrelevant message?

I am trying to compile engdemo.cpp on ubuntu. The gcc version is 6.4, but matlab recommends says 6.3, I am not sure if i need this exactly or if the hire version would work too. I have two questions.

1. When I put mex command in the commandline is get this message: This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015/Debian) (preloaded format=mex) restricted \write18 enabled. When I press enter from the keyboars I receive this message : Please type the name of your input file.

2. When I input the the commands 'mex -v -setup' and 'mex -v client engine engdemo.cpp', the following message is displayed:

pdfTeX 3.14159265-2.6-1.40.16 (TeX Live 2015/Debian) kpathsea version 6.2.1 Copyright 2015 Peter Breitenlohner (eTeX)/Han The Thanh (pdfTeX). There is NO warranty. Redistribution of this software is covered by the terms of both the pdfTeX copyright and the Lesser GNU General Public License. For more information about these matters, see the file named COPYING and the pdfTeX source. Primary author of pdfTeX: Peter Breitenlohner (eTeX)/Han The Thanh (pdfTeX). Compiled with libpng 1.6.17; using libpng 1.6.17 Compiled with zlib 1.2.8; using zlib 1.2.8 Compiled with poppler version 0.41.0

Please help to figure this out as I cannot see the compiled file