hjelm@g.gp.cs.cmu.edu (Mark Hjelm) (08/07/90)
What is the correct parse of:
int *const *volatile a;
a is a volatile pointer to a const pointer to an int or
a is a const pointer to a volatile pointer to an int?
Mark
hjelm@cs.cmu.edubright@sctc.com (Dave Bright) (08/08/90)
hjelm@g.gp.cs.cmu.edu (Mark Hjelm) writes: >What is the correct parse of: > int *const *volatile a; >a is a volatile pointer to a const pointer to an int or >a is a const pointer to a volatile pointer to an int? According to cdecl, choice #1: $ cdecl Type `help' or `?' for help cdecl> explain int *const *volatile a; declare a as volatile pointer to const pointer to int $ >hjelm@cs.cmu.edu -- David A. Bright Secure Computing Technology Corporation bright@SCTC.COM (work) 1210 West County Road E, Suite 100 dab@Bright.MN.ORG (home) Arden Hills, MN 55112
martin@mwtech.UUCP (Martin Weitzel) (08/09/90)
In article <10136@pt.cs.cmu.edu> hjelm@g.gp.cs.cmu.edu (Mark Hjelm) writes: > > >What is the correct parse of: > > int *const *volatile a; > >a is a volatile pointer to a const pointer to an int or >a is a const pointer to a volatile pointer to an int? You can ALLWAYS start with the name of the object (here: a), end with the type (here: int) and simply build your type description by concatenating what you encounter on your way "inside to out". So the first is the correct parsing. Because of this some people even prefer int const x; /* would read: x is a constant int */ over const int x; /* would read: x is an int constant */ Both have the same meaning in ANSI C - the first seems more "logical", but the second is (still) in more widespread use. -- Martin Weitzel, email: martin@mwtech.UUCP, voice: 49-(0)6151-6 56 83
gwyn@smoke.BRL.MIL (Doug Gwyn) (08/09/90)
In article <10136@pt.cs.cmu.edu> hjelm@g.gp.cs.cmu.edu (Mark Hjelm) writes:
-What is the correct parse of:
- int *const *volatile a;
-a is a volatile pointer to a const pointer to an int or
-a is a const pointer to a volatile pointer to an int?
The former. C declaration style is "contextual", so that whatever is
closest to the identifier happens first.mcdaniel@adi.com (Tim McDaniel) (08/15/90)
martin@mwtech.UUCP (Martin Weitzel) writes:
You can ALLWAYS start with the name of the object (here: a), end
with the type (here: int) and simply build your type description
by concatenating what you encounter on your way "inside to out".
So the first is the correct parsing.
Because of this some people even prefer
int const x; /* would read: x is a constant int */
over
const int x; /* would read: x is an int constant */
Both have the same meaning in ANSI C - the first seems more "logical",
but the second is (still) in more widespread use.
I thought so too, until I read K&R2 more closely. In the example
given above, "const" 'binds' to "int" rather than "x". So it differs
from the treatment of "*" in declarations (the only prefix operator in
declarations):
int * ip, i; /* ip is pointer to int, i is int */
int const ci, ci2; /* ci is const int, ci2 IS ALSO CONST INT */
Of less importance, "const" and "volatile" are special; in the middle
of a declaration, they can only appear immediately after a "*" token.
int *p, (*p2), *(p3); /* all are pointers to int */
int * const cpi; /* cpi is const pointer to int */
int (* const cpi2); /* cpi2 is const pointer to int */
int *(const cpi3); /* illegal: syntax error */
So you can't just use the inside-out construction rules blindly here:
you must remember that "const" is part of the type identifier, so
I consider "int const" to be misleading.
I think it would have been more consistent to treat "const" and
"volatile" in declarations just like "*", as a prefix unary operator.
It's now far too late.
--
--
Tim McDaniel
Internet: mcdaniel@adi.com UUCP: {uunet,sharkey}!amara!mcdaniel