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Re: Mistaken change in GCC (fwd)


GCC supports features that come from ISO standard C, and other
features which come from other origins but are just as important.  All
of these features should be kept working, both individually and
together.  We also want to add new extensions from time to
time--whenever we have good ideas for them.

Standards such as ISO C are very useful, and making GCC compile
standard programs with their standard meanings is also very useful.
But no standards committee is in charge of deciding what GCC should
do; we do not follow any standard slavishly.  We look at the standard,
and then we do what is most useful for us to do, which is usually a
matter of serving the needs of the users.

In many cases, what is useful for the users is to follow the standard.
Users have written many programs in accord with ISO C, and if GCC does
not compile them correctly, these users will be very disappointed with
GCC.  When following the standard is what the users need, we do it.
But we are not "obeying" the standard; we are satisfying users' needs
which were shaped by the standard.

In many other cases, whether we follow the standard is not directly
important for users.  For instance, the ISO C standard requires many
nonstandard constructs to be rejected.  We have instead defined
meanings for some of them as GNU C extensions.  This "violates" the
standard, but it is good for the users, since they find the extensions
useful.

GCC's default mode of operation does not entirely support ISO C; to
get 100% ISO C support requires certain options.  The default mode is
better, practically speaking, for the users than something strictl
defined by ISO C would be.

On rare occasions, a standard feature is so lousy that it should not
be enabled unless a user specifically requests it.  That is how we
handle trigraphs in GCC.

Sometimes it is useful to offer two modes, one which "obeys" the
standard, and another more useful mode which is the default.  That is
what --pedantic is for.  Many GNU C extensions get warnings if you use
--pedantic, so it is not usually a useful feature.  But it enables us
to say that "We have a mode that conforms entirely to the C standard".

Ten years ago, I believed we would need to be able to make a claim of
supporting the C standard perfectly in order for GCC to be a success.
Ten years ago, perhaps that was true.  Today, GCC could clearly
succeed without --pedantic.  But since --pedantic works, and some
people may use it, we should keep the feature working.

So please do not base any work on GCC on the idea that its goal is to
"compile standards-conforming ISO C programs".  Our goal is more than
that, and the rest of our goal must not be left out.


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