One compiler I need to use has problems with the following code:
---------------
#include <new.h>
class T {
public:
    T (int n) : _n (n) { }
    T (const T &ref) : _n (ref._n) { }
    ~T () { }

private:
    int _n;
};

void f ()
{
     T *ptr = new T [10] (1);  // line 14
}
---------------

In particular, it complains about the initializer to the vector new:
  CC: "test.cc", line 14: error: initializer for array of class object
     created using `new' (1248)

Another compiler has no problems with the code, and the one giving the
error message has not proved to be reliable.  The question is: Is this
legal C++?  I read thru 5.3.4 from the april draft and as far as I
understood the code was flagged ill-formed.  Did I interpret the draft
correctly?  If I did, how am I supposed to allocate an array of
objects of class T?  With explicit calls to operator new and placement
new?

BTW, is either comp.lang.c++.moderated or comp.std.c++ archived
somewhere?  I recall I have read something about this matter some time
back.

//LaT
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In article <l8291j9wix9.fsf@neppari.cs.hut.fi>,
"Lassi A. Tuura" <Lassi.Tuura@hut.fi> writes:
>One compiler I need to use has problems with the following code:
>---------------
>#include <new.h>
>class T {
>public:
>    T (int n) : _n (n) { }
>    T (const T &ref) : _n (ref._n) { }
>    ~T () { }
>
>private:
>    int _n;
>};
>
>void f ()
>{
>     T *ptr = new T [10] (1);  // line 14
>}
>---------------
>
>In particular, it complains about the initializer to the vector new:
>  CC: "test.cc", line 14: error: initializer for array of class object
>     created using `new' (1248)
>
>Another compiler has no problems with the code, and the one giving the
>error message has not proved to be reliable.  The question is: Is this
>legal C++?  I read thru 5.3.4 from the april draft and as far as I
>understood the code was flagged ill-formed.  Did I interpret the draft
>correctly?  If I did, how am I supposed to allocate an array of
>objects of class T?  With explicit calls to operator new and placement
>new?

The code is not legal. The reason is that the default constructor,
which is usually T::T(), will be used when you allocate arrays of T:s.
The compiler will generate a T::T() for you only in one case, namely
when you yourself have explicitly delared no other constructors. In
this case you have such a constructor, T::T(int n). Therefore the
compiler will not make a T::T() for you, which makes it impossible to
allocate arrays of T:s.

The fix is simple: Get yourself a T::T(). Another option is to give
the the int parameter a default value, usually 0 works OK. This would
give you this class:

class T
{
   public:
      T (int n = 0) : _n (n) { }
      T (const T &ref) : _n (ref._n) { }
      ~T () { }

   private:
      int _n;
};

A side note: Don't use "_" as a prefix to identifiers, since that is
almost illegal according to the language. It is much better to use "_"
as a suffix.

Mats Henricson
Stockholm
Sweden
---
[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
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"Lassi A. Tuura" <Lassi.Tuura@hut.fi> writes:

>BTW, is either comp.lang.c++.moderated or comp.std.c++ archived
>somewhere?  I recall I have read something about this matter some time
>back.

As far as I know, comp.std.c++ is not archived anywhere.
(Any volunteers for this task...?)

I do have a record of all of the articles that I have
approved for comp.std.c++ (i.e. roughly 1/3 of the articles
since Aug 95); it is 338k gzipped, and since I happened to
have it lying around, I've made it available for downloading
at <http://www.cs.mu.oz.au/~fjh/comp.std.c++/posted.log.gz>.

--
Fergus Henderson              WWW: http://www.cs.mu.oz.au/~fjh
fjh@cs.mu.oz.au               PGP: finger fjh@128.250.37.3
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[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
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