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"Peter Ammon" <> wrote in message
news:bnpfl8$mqb$...
> I'm calling random_shuffle without passing in a RandomNumberGenerator
> and getting the same shuffle every time I restart my program. Apparently
> I need to seed the internal random number generator. But how? I can't
> find any way to do that, and if there is none, then how is the internal
> random number generator useful?

With difficulty.

The Standard provides no function to do this, and random_shuffle is forbidden
from using std::rand(). C++ "inherits" rand() from C (see [lib.c.math] -- rand
isn't defined in the C++ Standard at all, instead a reference is given to the
C Standard), and C states that "The implementation shall behave as if no
library function calls the rand function".

This constraint thus applies to C++, which thus prevents random_shuffle from
using rand().

A resolution is proposed.
http://anubis.dkuug.dk/jtc1/sc22/wg2...ctive.html#395

--
Now Playing: Marc Aurel - Running (dumonde remix) (D I G I T A L L Y - I M P
O R T E D - European Trance, Techno, Hi-NRG... we can't define it!)


char a[99999],*p=a;main(c,V)char**V;{char*v=c>0?1[V]:V;if(c)for(;(c=*v)&&93^
c;p+=!(62^c)-!(60^c),*p+=!(43^c)-!(45^c),44^c||read(0,p,1),46^c||putchar(*p)
,91^c||(v=*p?main(-1,v+1),v-1:main(0,v)),++v);else for(;c+=!(91^*v)-!(93^*v)
;++v);return v;} /* brainf*** program as argv[1] */

In article <TT_ob.101487$>,
"DrPizza" <> wrote:

> "Peter Ammon" <> wrote in message
> news:bnpfl8$mqb$...
> > I'm calling random_shuffle without passing in a RandomNumberGenerator
> > and getting the same shuffle every time I restart my program. Apparently
> > I need to seed the internal random number generator. But how? I can't
> > find any way to do that, and if there is none, then how is the internal
> > random number generator useful?
>
> With difficulty.
>
> The Standard provides no function to do this, and random_shuffle is forbidden
> from using std::rand(). C++ "inherits" rand() from C (see [lib.c.math] -- rand
> isn't defined in the C++ Standard at all, instead a reference is given to the
> C Standard), and C states that "The implementation shall behave as if no
> library function calls the rand function".
>
> This constraint thus applies to C++, which thus prevents random_shuffle from
> using rand().
>
> A resolution is proposed.
> http://anubis.dkuug.dk/jtc1/sc22/wg2...ctive.html#395

And just fyi, the resolution was looked upon favoribly at last week's
standards meeting. If I remember correctly, its status was moved to
"ready". But don't take that to the bank until the next revision of the
issues list comes out.

-Howard

DrPizza wrote:
>
> "Peter Ammon" <> wrote in message
> news:bnpfl8$mqb$...
> > I'm calling random_shuffle without passing in a RandomNumberGenerator
> > and getting the same shuffle every time I restart my program. Apparently
> > I need to seed the internal random number generator. But how? I can't
> > find any way to do that, and if there is none, then how is the internal
> > random number generator useful?
>
> With difficulty.
>
> The Standard provides no function to do this, and random_shuffle is forbidden
> from using std::rand(). C++ "inherits" rand() from C (see [lib.c.math] -- rand
> isn't defined in the C++ Standard at all, instead a reference is given to the
> C Standard), and C states that "The implementation shall behave as if no
> library function calls the rand function".
>
> This constraint thus applies to C++, which thus prevents random_shuffle from
> using rand().
>
> A resolution is proposed.
> http://anubis.dkuug.dk/jtc1/sc22/wg2...ctive.html#395
>

Yup, we added redundant language to make it clear that statements in the
C standard about the C library are not constraints on the C++ library.
Shouldn't need to be said...

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

"Pete Becker" <> wrote in message
news:...
> DrPizza wrote:
> >
> > "Peter Ammon" <> wrote in message
> > news:bnpfl8$mqb$...
> > > I'm calling random_shuffle without passing in a RandomNumberGenerator
> > > and getting the same shuffle every time I restart my program. Apparently
> > > I need to seed the internal random number generator. But how? I can't
> > > find any way to do that, and if there is none, then how is the internal
> > > random number generator useful?
> >
> > With difficulty.
> >
> > The Standard provides no function to do this, and random_shuffle is
forbidden
> > from using std::rand(). C++ "inherits" rand() from C (see [lib.c.math] --
rand
> > isn't defined in the C++ Standard at all, instead a reference is given to
the
> > C Standard), and C states that "The implementation shall behave as if no
> > library function calls the rand function".
> >
> > This constraint thus applies to C++, which thus prevents random_shuffle
from
> > using rand().
> >
> > A resolution is proposed.
> > http://anubis.dkuug.dk/jtc1/sc22/wg2...ctive.html#395
> >
>
> Yup, we added redundant language to make it clear that statements in the
> C standard about the C library are not constraints on the C++ library.
> Shouldn't need to be said...

Why not? You wouldn't want to permit your C++ library to call strtok()
internally, would you? In general it seems quite desirable to carry that
constraint over from C; rand() is probably the only exception.

--
Now Playing: Accuface - Theme From Accuface


char a[99999],*p=a;main(c,V)char**V;{char*v=c>0?1[V]:V;if(c)for(;(c=*v)&&93^
c;p+=!(62^c)-!(60^c),*p+=!(43^c)-!(45^c),44^c||read(0,p,1),46^c||putchar(*p)
,91^c||(v=*p?main(-1,v+1),v-1:main(0,v)),++v);else for(;c+=!(91^*v)-!(93^*v)
;++v);return v;} /* brainf*** program as argv[1] */

DrPizza wrote:
>
> You wouldn't want to permit your C++ library to call strtok()
> internally, would you?

Sure. Why not?

> In general it seems quite desirable to carry that
> constraint over from C; rand() is probably the only exception.
>

"Seems quite desirable" is not the same as "required by the standard."

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

"Pete Becker" <> wrote in message
news:...
> DrPizza wrote:
> >
> > You wouldn't want to permit your C++ library to call strtok()
> > internally, would you?
>
> Sure. Why not?
Because it means you can't use strtok() yourself?

> > In general it seems quite desirable to carry that
> > constraint over from C; rand() is probably the only exception.
> "Seems quite desirable" is not the same as "required by the standard."
But it (surely) is required by the standard because the standard just defers
to the C standard for the description of these functions, and one aspect of
the C standard pertinent to these functions is that the implementation shall
not call them.


--
char a[99999],*p=a;main(c,V)char**V;{char*v=c>0?1[V]:V;if(c)for(;(c=*v)&&93^
c;p+=!(62^c)-!(60^c),*p+=!(43^c)-!(45^c),44^c||read(0,p,1),46^c||putchar(*p)
,91^c||(v=*p?main(-1,v+1),v-1:main(0,v)),++v);else for(;c+=!(91^*v)-!(93^*v)
;++v);return v;} /* brainf*** program as argv[1] */

On Thu, 6 Nov 2003 13:19:32 -0000, "DrPizza"
<> wrote:

>> > In general it seems quite desirable to carry that
>> > constraint over from C; rand() is probably the only exception.
>> "Seems quite desirable" is not the same as "required by the standard."
>But it (surely) is required by the standard because the standard just defers
>to the C standard for the description of these functions, and one aspect of
>the C standard pertinent to these functions is that the implementation shall
>not call them.

The C standard only says that the implementation of the C library
won't call them.

Taking the original quote:
"The implementation shall behave as if no library function calls the
rand function"

The "library" referred to is the C library, not the C++ one. Just
because C++ includes the (slightly modified) C library doesn't mean
that it *is* the C library.

Tom

DrPizza wrote:
>
> "Pete Becker" <> wrote in message
> news:...
> > DrPizza wrote:
> > >
> > > You wouldn't want to permit your C++ library to call strtok()
> > > internally, would you?
> >
> > Sure. Why not?
> Because it means you can't use strtok() yourself?

Non sequitur.

>
> > > In general it seems quite desirable to carry that
> > > constraint over from C; rand() is probably the only exception.
> > "Seems quite desirable" is not the same as "required by the standard."
> But it (surely) is required by the standard because the standard just defers
> to the C standard for the description of these functions, and one aspect of
> the C standard pertinent to these functions is that the implementation shall
> not call them.
>

The C++ standard does not change that constraint. No C function calls
rand.

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

"tom_usenet" <> wrote in message
news:...
> The C standard only says that the implementation of the C library
> won't call them.
Well, no, it doesn't, it simply says that the implementation shall behave as
if no library function calls rand. It doesn't specify which library.

> Taking the original quote:
> "The implementation shall behave as if no library function calls the
> rand function"
>
> The "library" referred to is the C library, not the C++ one. Just
> because C++ includes the (slightly modified) C library doesn't mean
> that it *is* the C library.
Upon incorporation into C++, "the library" refers to the C++ library. The C++
library is the only library there is, so it's the only one it could refer to.


--
Now Playing: Daft Punk - Around The World


char a[99999],*p=a;main(c,V)char**V;{char*v=c>0?1[V]:V;if(c)for(;(c=*v)&&93^
c;p+=!(62^c)-!(60^c),*p+=!(43^c)-!(45^c),44^c||read(0,p,1),46^c||putchar(*p)
,91^c||(v=*p?main(-1,v+1),v-1:main(0,v)),++v);else for(;c+=!(91^*v)-!(93^*v)
;++v);return v;} /* brainf*** program as argv[1] */

"Pete Becker" <> wrote in message
news:...
> DrPizza wrote:
> >
> > "Pete Becker" <> wrote in message
> > news:...
> > > DrPizza wrote:
> > > >
> > > > You wouldn't want to permit your C++ library to call strtok()
> > > > internally, would you?
> > >
> > > Sure. Why not?
> > Because it means you can't use strtok() yourself?
> Non sequitur.
If the implementation can call strtok() then I can't be sure what state
strtok()'s static buffer is in -- it need not be in the state I left it in.
This renders strtok() useless. If I use it I risk ****ing up the library; if
the library uses it it risks ****ing up my program.

> The C++ standard does not change that constraint. No C function calls
> rand.
Except the "not called by the library" statement refers only to the library of
the implementation, not the C library. Given that in C++ the implementation
is one of C++, and the library is that of C++, the restriction should constain
the C++ library too.


--
Now Playing: Daft Punk - Around The World


char a[99999],*p=a;main(c,V)char**V;{char*v=c>0?1[V]:V;if(c)for(;(c=*v)&&93^
c;p+=!(62^c)-!(60^c),*p+=!(43^c)-!(45^c),44^c||read(0,p,1),46^c||putchar(*p)
,91^c||(v=*p?main(-1,v+1),v-1:main(0,v)),++v);else for(;c+=!(91^*v)-!(93^*v)
;++v);return v;} /* brainf*** program as argv[1] */