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Hi

I am going to design and implement a typical library for rational
numbers, something like
Boost.Rational. My class is actually implemented as a template, in a
similar manner to the standard complex class.
I want to handle Whole numbers like rational numbers; As you know,
from point of math view
whole numbers are subset of rational numbers, for example 3 is 3/1.
I like to read both kind of numbers (whole and fraction) in a single
operator>> function. I mean
I want to handle
a
a/b
together. I finally ended with an assumption: Immediately, after
numerator, I should get '/':
template<class T>
std::istream& operator>>(std::istream& is, rational<T>& r)
{
/*
handle the following foramts:
n/d
n
*/
T n, d;
char c = 0; // for '/'
is >> n;
if (is.good()) {
is.get(c);
}
if (c == '/') { // fraction
if (is.good())
is >> d;
}
else if (std::isspace(c) || is.rdstate() & std::ios_base::eofbit)
{ // whole number
d = 1;
}
else {
is.clear(std::ios_base::badbit); // set state
}

if (is) // everything is good
r = rational<T>(n, d);

return is;
}

I know, my code may be inefficient.
Any suggestion for better/more elegant handling different formats and
better efficiency?

Thanks in advance,
-- Saeed Amrollahi

On Nov 15, 4:07 pm, Saeed Amrollahi <amrollahi.sa...@gmail.com> wrote:
> I am going to design and implement a typical library for
> rational numbers, something like Boost.Rational. My class is
> actually implemented as a template, in a similar manner to the
> standard complex class. I want to handle Whole numbers like
> rational numbers; As you know, from point of math view whole
> numbers are subset of rational numbers, for example 3 is 3/1.
> I like to read both kind of numbers (whole and fraction) in a
> single operator>> function. I mean I want to handle
> a
> a/b
> together. I finally ended with an assumption: Immediately,
> after numerator, I should get '/':

> template<class T>
> std::istream& operator>>(std::istream& is, rational<T>& r)
> {
> /*
> handle the following foramts:
> n/d
> n
> */
> T n, d;
> char c = 0; // for '/'
> is >> n;
> if (is.good()) {
> is.get(c);
> }
> if (c == '/') { // fraction
> if (is.good())
> is >> d;
> }
> else if (std::isspace(c) || is.rdstate() & std::ios_base::eofbit)
> { // whole number
> d = 1;
> }
> else {
> is.clear(std::ios_base::badbit); // set state
> }
> if (is) // everything is good
> r = rational<T>(n, d);
> return is;
> }

> I know, my code may be inefficient.
> Any suggestion for better/more elegant handling different
> formats and better efficiency?

I'm not too sure about your error handling, and your logic. If
nothing else, you're extracting one character too many when
reading just a whole number. (Think of something like 3+1/3.)
What's wrong with something simple like:

T n;
is >> n;
T d(1); // T must support conversion from int.
if ( is.peek() == '/' ) {
is.get(); // extract '/'
is >> d;
}
if ( is ) {
r = rational<T>( n, d );
}
return is;

This leaves all of the error handling up to >>T, and seems
overall the simplest solution.

--
James Kanze

On Nov 16, 12:01*pm, James Kanze <james.ka...@gmail.com> wrote:
> On Nov 15, 4:07 pm, Saeed Amrollahi <amrollahi.sa...@gmail.com> wrote:
>
>
>
>
>
> > I am going to design and implement a typical library for
> > rational numbers, something like Boost.Rational. My class is
> > actually implemented as a template, in a similar manner to the
> > standard complex class. *I want to handle Whole numbers like
> > rational numbers; As you know, from point of math view whole
> > numbers are subset of rational numbers, for example 3 is 3/1.
> > I like to read both kind of numbers (whole and fraction) in a
> > single operator>> function. I mean I want to handle
> > * a
> > * a/b
> > together. I finally ended with an assumption: Immediately,
> > after numerator, I should get '/':
> > template<class T>
> > std::istream& operator>>(std::istream& is, rational<T>& r)
> > {
> > * /*
> > * * handle the following foramts:
> > * * n/d
> > * * n
> > * */
> > * T n, d;
> > * char c = 0; // for '/'
> > * is >> n;
> > * if (is.good()) {
> > * * is.get(c);
> > * }
> > * if (c == '/') { // fraction
> > * * if (is.good())
> > * * * * is >> d;
> > * }
> > *else if (std::isspace(c) || is.rdstate() & std::ios_base::eofbit)
> > { // whole number
> > * * d = 1;
> > * }
> > * else {
> > * * is.clear(std::ios_base::badbit); // set state
> > * }
> > * if (is) // everything is good
> > * * r = rational<T>(n, d);
> > * return is;
> > }
> > I know, my code may be inefficient.
> > Any suggestion for better/more elegant handling different
> > formats and better efficiency?
>
> I'm not too sure about your error handling, and your logic. *If
> nothing else, you're extracting one character too many when
> reading just a whole number. *(Think of something like 3+1/3.)
> What's wrong with something simple like:
>
> * * T n;
> * * is >> n;
> * * T d(1); * *// *T must support conversion from int.
> * * if ( is.peek() == '/' ) {
> * * * * is.get(); * * * // *extract '/'
> * * * * is >> d;
> * * }
> * * if ( is ) {
> * * * * r = rational<T>( n, d );
> * * }
> * * return is;
>
> This leaves all of the error handling up to >>T, and seems
> overall the simplest solution.
>
> --
> James Kanze- Hide quoted text -
>
> - Show quoted text -

Hi James
Thank you for your feedback.
The template parameter T is an Integral type.
My main problem is:
Is there any solution to read a fraction and whole number in formatted
way
rather than using unformatted (get function)? I guess there is no way.
So I assumed, if user wants to enter a whole number, (s)he have to
enter in
one line. So, I use isspace() and ios_base::eofbit.
for a fraction my assumption is: if user wants to enter a fraction, (s)
he have to
enter '/' immediately after numerator. Your code somehow reflects
that.
Of course your code is simple and elegant and my code is somehow
sloppy.

Please throw light.
-- Saeed Amrollahi

On Nov 16, 9:26 am, Saeed Amrollahi <amrollahi.sa...@gmail.com> wrote:
> On Nov 16, 12:01 pm, James Kanze <james.ka...@gmail.com> wrote:

[...]
> > I'm not too sure about your error handling, and your logic.
> > If nothing else, you're extracting one character too many
> > when reading just a whole number. (Think of something like
> > 3+1/3.) What's wrong with something simple like:

> > T n;
> > is >> n;
> > T d(1); // T must support conversion from int.
> > if ( is.peek() == '/' ) {
> > is.get(); // extract '/'
> > is >> d;
> > }
> > if ( is ) {
> > r = rational<T>( n, d );
> > }
> > return is;

> > This leaves all of the error handling up to >>T, and seems
> > overall the simplest solution.


> Thank you for your feedback.
> The template parameter T is an Integral type.

I more or less guessed that. Although you might want to ask
yourself what will happen if someone instantiates your template
on double, or even std::string.

> My main problem is:
> Is there any solution to read a fraction and whole number in
> formatted way rather than using unformatted (get function)?

I'm not sure what you really mean by "formatted" way? You want
to look at a single character, without extracting it;
istream:eek is the function which does that.

There is one weakness in my quicky solution above: it doesn't
allow white space before the '/', but allows it after. This
could easily be fixed by verifying that the character after the
'/' is not white space (getting it, again, using peek()), or by
skipping white space before checking for the '/'.

> I guess there is no way. So I assumed, if user wants to enter
> a whole number, (s)he have to enter in one line.

Not with the above. The above will read a number. If the
character immediately following the number is a '/', it skips
this, and reads a second number. Otherwise, it stops with the
number, removing no more characters.

> So, I use isspace() and ios_base::eofbit.

That was the point I didn't fully understand in the original
code. Is the fact that you only read the numerator (and use 1
for the denominator) determined by the fact that the first
number is immediately followed by a '/', or by the fact that it
was followed by white space or the end of file. In other words,
what was the desired behavior when reading something like:
43,x
Should the extractor extract the 43, return 43/1, and leave the
input positionned on the ',', or should it set failbit to
indicate a format error on input. (My version does the first.)

> for a fraction my assumption is: if user wants to enter a
> fraction, (s) he have to enter '/' immediately after
> numerator. Your code somehow reflects that.

My code does that exactly. If the first character after the
number in the stream is a '/', it skips it, and attempts to read
a denominator. Otherwise, it uses the default value 1 as
denominator.

--
James Kanze

On Nov 16, 9:20*pm, James Kanze <james.ka...@gmail.com> wrote:
> On Nov 16, 9:26 am, Saeed Amrollahi <amrollahi.sa...@gmail.com> wrote:
>
> > On Nov 16, 12:01 pm, James Kanze <james.ka...@gmail.com> wrote:
>
> * * [...]
>
>
>
>
>
> > > I'm not too sure about your error handling, and your logic.
> > > If nothing else, you're extracting one character too many
> > > when reading just a whole number. *(Think of something like
> > > 3+1/3.) What's wrong with something simple like:
> > > * * T n;
> > > * * is >> n;
> > > * * T d(1); * *// *T must support conversion from int.
> > > * * if ( is.peek() == '/' ) {
> > > * * * * is.get(); * * * // *extract '/'
> > > * * * * is >> d;
> > > * * }
> > > * * if ( is ) {
> > > * * * * r = rational<T>( n, d );
> > > * * }
> > > * * return is;
> > > This leaves all of the error handling up to >>T, and seems
> > > overall the simplest solution.
> > Thank you for your feedback.
> > The template parameter T is an Integral type.
>
> I more or less guessed that. *Although you might want to ask
> yourself what will happen if someone instantiates your template
> on double, or even std::string.
>
> > My main problem is:
> > Is there any solution to read a fraction and whole number in
> > formatted way rather than using unformatted (get function)?
>
> I'm not sure what you really mean by "formatted" way? *You want
> to look at a single character, without extracting it;
> istream:eek is the function which does that.
>
> There is one weakness in my quicky solution above: it doesn't
> allow white space before the '/', but allows it after. *This
> could easily be fixed by verifying that the character after the
> '/' is not white space (getting it, again, using peek()), or by
> skipping white space before checking for the '/'.
>
> > I guess there is no way. *So I assumed, if user wants to enter
> > a whole number, (s)he have to enter in one line.
>
> Not with the above. *The above will read a number. *If the
> character immediately following the number is a '/', it skips
> this, and reads a second number. *Otherwise, it stops with the
> number, removing no more characters.
>
> > So, I use isspace() and ios_base::eofbit.
>
> That was the point I didn't fully understand in the original
> code. *Is the fact that you only read the numerator (and use 1
> for the denominator) determined by the fact that the first
> number is immediately followed by a '/', or by the fact that it
> was followed by white space or the end of file. *In other words,
> what was the desired behavior when reading something like:
> * * 43,x
> Should the extractor extract the 43, return 43/1, and leave the
> input positionned on the ',', or should it set failbit to
> indicate a format error on input. *(My version does the first.)
>
> > for a fraction my assumption is: if user wants to enter a
> > fraction, (s) he have to enter '/' immediately after
> > numerator. Your code somehow reflects that.
>
> My code does that exactly. *If the first character after the
> number in the stream is a '/', it skips it, and attempts to read
> a denominator. *Otherwise, it uses the default value 1 as
> denominator.
>
> --
> James Kanze- Hide quoted text -
>
> - Show quoted text -

Thanks for your feedback
-- Saeed Amrollahi