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(standards.info)Using Extensions

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Using Non-standard Features
===========================

   Many GNU facilities that already exist support a number of convenient
extensions over the comparable Unix facilities.  Whether to use these
extensions in implementing your program is a difficult question.

   On the one hand, using the extensions can make a cleaner program.
On the other hand, people will not be able to build the program unless
the other GNU tools are available.  This might cause the program to
work on fewer kinds of machines.

   With some extensions, it might be easy to provide both alternatives.
For example, you can define functions with a "keyword" `INLINE' and
define that as a macro to expand into either `inline' or nothing,
depending on the compiler.

   In general, perhaps it is best not to use the extensions if you can
straightforwardly do without them, but to use the extensions if they
are a big improvement.

   An exception to this rule are the large, established programs (such
as Emacs) which run on a great variety of systems.  Using GNU
extensions in such programs would make many users unhappy, so we don't
do that.

   Another exception is for programs that are used as part of
compilation: anything that must be compiled with other compilers in
order to bootstrap the GNU compilation facilities.  If these require
the GNU compiler, then no one can compile them without having them
installed already.  That would be extremely troublesome in certain
cases.