Re: pointer to pointer

From:
"Joshua Lehrer" <usenet_cpp@lehrerfamily.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Fri, 2 Mar 2007 13:14:40 CST
Message-ID:
<1172858825.330285.155100@p10g2000cwp.googlegroups.com>
On Feb 26, 10:19 pm, cbarr...@ix.netcom.com (Carl Barron) wrote:

Mitesh <oopsbab...@hotmail.com> wrote:
   A pointer to a pointer might be used when ever another level of
indirection simplifies the problem.
   remember also
   double *a = ...;
   double *b = ...;
   tyoedef double *Ptr;


you mean 'typedef' :)

   Ptr & c = a;
   Ptr * d = a;


You left off an ampersand
Ptr * d = &a;

   c = b // modifies a (a = b)
   d = b // does not modify a


Nor does it even compile. 'd' is a pointer to a pointer. 'b' is a
pointer. The later can not be assigned to the former.

Pointer-to-pointer is just as useful as reference-to-pointer, except
pointer-to-pointer can be null, while reference-to-pointer can not be
null.

As others have pointed out, a common use case is an object factory:

void create(T** pp) {
  if (pp) *pp = new T();
}
void create(T*& rp) {
  rp = new T();
}

joshua lehrer
http://www.lehrerfamily.com/

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