Default parameters of constructors

[Marcin Vorbrodt]

I know that the default parameter(s) of a constructor can be either
hardcoded values or function calls. But can they be calls to static class
methods as well... example:

Constructor of my CoordinateFrame class:

CoordinateFrame (const Basis &basis = Basis::ORIGIN() , const Point &origin =
Point::ORIGIN() );

Thanks,
Martin

[Marcin Vorbrodt]

Re: Default parameters of constructors


"Mike Wahler" <mkwahler@mkwah ler.net> wrote in message
news:KWK6b.2683 $PE6.965@newsre ad3.news.pas.ea rthlink.net...[color=blue]
>
> Marcin Vorbrodt <mvorbro@eos.nc su.edu> wrote in message
> news:bjer80$906 $2@uni00nw.unit y.ncsu.edu...[color=green]
> > I know that the default parameter(s) of a constructor can be either
> > hardcoded values or function calls. But can they be calls to static[/color][/color]
class[color=blue][color=green]
> > methods as well... example:
> >
> > Constructor of my CoordinateFrame class:
> >
> > CoordinateFrame (const Basis &basis = Basis::ORIGIN() , const Point[/color][/color]
&origin[color=blue]
> =[color=green]
> > Point::ORIGIN() );[/color]
>
> Are you getting compiler errors or what? If so, what are they,
> and what exact code causes them?
>
> #include <iostream>
>
> class A
> {
> public:
> static int foo() { return 1; }
> };
>
> class B
> {
> public:
> static int foo() { return 2; }
> };
>
> class C
> {
> public:
> int membera;
> int memberb;
>
> C(int parma = A::foo(), int parmb = B::foo())
> : membera(parma), memberb(parmb) {}
> };
>
> int main()
> {
> C c;
> std::cout << c.membera << ", " << c.memberb << '\n';
> return 0;
> }
>
> Output:
>
> 1, 2
>
> -Mike
>
>
>[/color]

No, no compiler errors at all. I was just wondering if that was allowed by
the C++ standard, or simply a glitch in my compiler;-)

Martin

[Marcin Vorbrodt]

Re: Default parameters of constructors


"Mike Wahler" <mkwahler@mkwah ler.net> wrote in message
news:obO6b.2841 $PE6.1823@newsr ead3.news.pas.e arthlink.net...[color=blue]
>
> Marcin Vorbrodt <mvorbro@eos.nc su.edu> wrote in message
> news:bjfvuu$pro $1@uni00nw.unit y.ncsu.edu...[color=green]
> >
> > "Mike Wahler" <mkwahler@mkwah ler.net> wrote in message
> > news:KWK6b.2683 $PE6.965@newsre ad3.news.pas.ea rthlink.net...[color=darkred]
> > >
> > > Marcin Vorbrodt <mvorbro@eos.nc su.edu> wrote in message
> > > news:bjer80$906 $2@uni00nw.unit y.ncsu.edu...
> > > > I know that the default parameter(s) of a constructor can be either
> > > > hardcoded values or function calls. But can they be calls to static[/color]
> > class[color=darkred]
> > > > methods as well... example:
> > > >
> > > > Constructor of my CoordinateFrame class:
> > > >
> > > > CoordinateFrame (const Basis &basis = Basis::ORIGIN() , const Point[/color]
> > &origin[color=darkred]
> > > =
> > > > Point::ORIGIN() );
> > >
> > > Are you getting compiler errors or what? If so, what are they,
> > > and what exact code causes them?
> > >
> > > #include <iostream>
> > >
> > > class A
> > > {
> > > public:
> > > static int foo() { return 1; }
> > > };
> > >
> > > class B
> > > {
> > > public:
> > > static int foo() { return 2; }
> > > };
> > >
> > > class C
> > > {
> > > public:
> > > int membera;
> > > int memberb;
> > >
> > > C(int parma = A::foo(), int parmb = B::foo())
> > > : membera(parma), memberb(parmb) {}
> > > };
> > >
> > > int main()
> > > {
> > > C c;
> > > std::cout << c.membera << ", " << c.memberb << '\n';
> > > return 0;
> > > }
> > >
> > > Output:
> > >
> > > 1, 2
> > >
> > > -Mike
> > >
> > >
> > >[/color]
> >
> > No, no compiler errors at all. I was just wondering if that was allowed[/color][/color]
by[color=blue][color=green]
> > the C++ standard, or simply a glitch in my compiler;-)[/color]
>
> Well, it's good that you check. I'm fairly sure it's valid, I'll
> have to check the standard to be sure. No time right now, but
> I'll post my findings when I return (unless of course someone else
> beats me to it. :-) )
>
> -Mike
>
>
>[/color]

Great, cant wait to hear back from you.

Martin

[Janusz Szpilewski]

Re: Default parameters of constructors

Mike Wahler wrote:
[color=blue]
> Well, it's good that you check. I'm fairly sure it's valid, I'll
> have to check the standard to be sure. No time right now, but
> I'll post my findings when I return (unless of course someone else
> beats me to it. :-) )
>[/color]

The C++ standard forbids the default parameters being local variables
(8.3.6/7) or the keyword this (8.3.6/8). I cannot think of any inherent
reason why constructor might clash with a static member function. Seen
from the run-time environment point of view they are completely unrelated.

Regards,
Janusz

[Mike Wahler]

Re: Default parameters of constructors

Marcin Vorbrodt <mvorbro@eos.nc su.edu> wrote in message
news:bjgc11$7oe $1@uni00nw.unit y.ncsu.edu...

[using the return value of a static member function
as a default function parameter]
[color=blue][color=green][color=darkred]
> > > No, no compiler errors at all. I was just wondering if that was[/color][/color][/color]
allowed[color=blue]
> by[color=green][color=darkred]
> > > the C++ standard, or simply a glitch in my compiler;-)[/color]
> >
> > Well, it's good that you check. I'm fairly sure it's valid, I'll
> > have to check the standard to be sure. No time right now, but
> > I'll post my findings when I return (unless of course someone else
> > beats me to it. :-) )
> >
> > -Mike
> >
> >
> >[/color]
>
> Great, cant wait to hear back from you.[/color]

What you're doing is valid, according to 8.3.6
Also note that this issue does not only apply
to constructors, but to any function.

-Mike