🚀 go-pugleaf

    If an enterprise  uses g++ to create programs that are to be sold,
    are these applications under any restrictions ?

g++: no.
libg++: yes, they fall under the GNU public licence.  A copy is
available with all GNU software in the file COPYING, or mail
gnu@prep.ai.mit.edu, or phone the office (ask information for the Free
Software Foundation in Cambridge, MA).

However, the foundation is considering changing the terms for
libraries.  For more information see the June GNUs bulletin (phone the
office and ask for a paper copy, or I assume gnu@prep.ai.mit.edu for
an e-mail copy).

    In general terms : what kind of consequences does one have by using a
    gnu product ?

For most products, none.  The mere fact of editing your file with
emacs doesn't change who owns it.  However, for programs like
libraries or bison part of the GNU code is copied into your
executable, putting the executable under the terms of the GNU General
Public License.