~traits::eof()?

[Mark A. Gibbs]

Good day,

What is the safest way to get a non-end of file value?
char_traits<cha r_type>::eof() will get me eof, but how can I safely and
consistently generate a value that is not eof? should i use
~char_traits<ch ar_type>::eof() ? char_traits<cha r_type>::int_ty pe()?
char_traits<cha r_type>::eof() + 1?
while(!char_tra its<char_type>: :not_eof(char_t raits<char_type >::int_type(ran d())))?

mark

[Mark A. Gibbs]

P.J. Plauger wrote:

the like. but is there no simple way to generate a value of type
char_traits<c har_type>::int_ type that is guaranteed to satisfy
char_traits<c har_type>::not_ eof()?

Only if you have a candidate "character" in hand that you assuredly
want *not* turned into an eof. That's what not_eof is for.

am i the only one that finds that odd? if you have a candidate
"character" (int_type) in hand, and you want to be assured that you do
not have eof, wouldn't it have been more straightforward to have:

int_type d = eq_int_type(c, eof()) ? not_eof_charact er() : c;

at least then d is well defined.
That's a helluva way to earn royalties, adding a nonstandard patch
to a kludge to an inelegant design.

hey, i wouldn't be the first!

int_type overflow(int_ty pe c = traits::eof())
{
// whatever
return (success) ? traits::not_eof (c) : traits::eof();
}

would that be guaranteed to work as expected?

Once you permit a valid character code to pun with eof(), it's hard
to say what "work" means anymore.

sorry, what was that? just in case i wasn't clear, this overflow() is
basic_streambuf ::overflow(). basic_streambuf ::overflow() is supposed to
return eof() on failure, anything else otherwise (exactly what is
unspecified). the input character may be eof().

what way is there to possibly satisfy these conditions besides the line
above (or does that not work either)?

mark

[Mark A. Gibbs]

P.J. Plauger wrote:

ah, so traits::eof() can never be 0. perfect. thank you.

How did you deduce that? It's almost certainly true, but I doubt
that it's guaranteed.

by assuming that i could use the result of not_eof() in a boolean
expression, which i now realize was not correct. the name threw me off
:/ sorry.

if all not_eof() is good for is guaranteeing a non-eof value, why does
it need the parameter? is it that worth the little convenience of
getting back a known result *most* of the time?

mark

[P.J. Plauger]

"Mark A. Gibbs" <x_*********@ro gers.com_x> wrote in message
news:F2******** *************@t wister01.bloor. is.net.cable.ro gers.com...

P.J. Plauger wrote:

the like. but is there no simple way to generate a value of type
char_traits<c har_type>::int_ type that is guaranteed to satisfy
char_traits<c har_type>::not_ eof()?

Only if you have a candidate "character" in hand that you assuredly
want *not* turned into an eof. That's what not_eof is for.

am i the only one that finds that odd? if you have a candidate
"character" (int_type) in hand, and you want to be assured that you do
not have eof, wouldn't it have been more straightforward to have:

int_type d = eq_int_type(c, eof()) ? not_eof_charact er() : c;

at least then d is well defined.

You're not the only one. See my comment immediately below.

That's a helluva way to earn royalties, adding a nonstandard patch
to a kludge to an inelegant design.

hey, i wouldn't be the first!

int_type overflow(int_ty pe c = traits::eof())
{
// whatever
return (success) ? traits::not_eof (c) : traits::eof();
}

would that be guaranteed to work as expected?

Once you permit a valid character code to pun with eof(), it's hard
to say what "work" means anymore.

sorry, what was that? just in case i wasn't clear, this overflow() is
basic_streambuf ::overflow(). basic_streambuf ::overflow() is supposed to
return eof() on failure, anything else otherwise (exactly what is
unspecified). the input character may be eof().

what way is there to possibly satisfy these conditions besides the line
above (or does that not work either)?

IIRC, you were muddling in the possibility that eof() could return zero.

P.J. Plauger
Dinkumware, Ltd.
http://www.dinkumware.com