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From: andy@cit-vax.Caltech.Edu (Andy Fyfe)
Newsgroups: comp.std.c
Subject: the "const" qualifier
Message-ID: <12239@cit-vax.Caltech.Edu>
Date: 15 Oct 89 04:52:07 GMT
Reply-To: andy@csvax.caltech.edu (Andy Fyfe)
Organization: California Institute of Technology
Lines: 24

The GNU C compiler permits assignment (where assignment includes
things such as parameter passing) of a "char *" to a "const char *",
but not of a "char **" to a "const char **" without an explicit
cast.  Rms assures me that this is in strict accordance with the
ANSI standard.

This came up when I provided the following prototype for
execv:
	extern int execv(const char *path, const char **args);
Gcc gave a warning about incompatible pointer types when execv was
called with a "char **" as the second parameter.

While "execv" may be a bad example (as it's not expected to
return at all), my understanding of such a prototype is that the
function will not change the characters pointed to by "path", or
by "args[0], args[1], ...".  Passing pointers that permit such
changes I would expect to be allowed (and is, for "path").

I was wondering if someone could clarify this for me.

Andy Fyfe
            andy@csvax.caltech.edu
            wjafyfe@caltech.bitnet
            andy@cit-vax.UUCP	(...!ames!elroy!cit-vax!andy)