Strange error with iterators

[Michael Coley]

Hi, I've wrote this function which should add a comma for every 3
digits in a number (so that it looks something like 5,000).

This is my function:
std::string formatNumber(in t number)
{
// Convert the int to a string.
std::string numString = boost::lexical_ cast<std::strin g>(number);

std::string::co nst_reverse_ite rator i = numString.rbegi n(), end =
numString.rend( );
for (int j = 0; i != end; ++i, ++j)
{
// Add a comma every three places.
if (j < 3)
{
// ERROR HAPPENS ON THIS LINE BELOW.
i = numString.inser t(i + 1, ',');
end = numString.rend( );

j = 0;
}
}

return numString;
}

I get an error saying it cannot convert from reverse_iterato r to
unsigned int. It looks to me as if it's trying to call the wrong
overloaded function, as I did a search on the method and I can indeed
pass an iterator and a char.

Can anybody tell me why this is failing?

Thanks in advance.

[Richard Herring]

In message <11************ **********@q3g2 000prf.googlegr oups.com>,
Michael Coley <m1****@googlem ail.comwrites

>Hi, I've wrote this function which should add a comma for every 3
digits in a number (so that it looks something like 5,000).

This is my function:
std::string formatNumber(in t number)
{
// Convert the int to a string.
std::string numString = boost::lexical_ cast<std::strin g>(number);

std::string::co nst_reverse_ite rator i = numString.rbegi n(), end =
numString.rend ();
for (int j = 0; i != end; ++i, ++j)
{
// Add a comma every three places.
if (j < 3)
{
// ERROR HAPPENS ON THIS LINE BELOW.
i = numString.inser t(i + 1, ',');
end = numString.rend( );

j = 0;
}
}

return numString;
}

I get an error saying it cannot convert from reverse_iterato r to
unsigned int. It looks to me as if it's trying to call the wrong
overloaded function, as I did a search on the method and I can indeed
pass an iterator and a char.

i+1 isn't an iterator, it's a const_reverse_i terator

--
Richard Herring

[Victor Bazarov]

Michael Coley wrote:

Hi, I've wrote this function which should add a comma for every 3
digits in a number (so that it looks something like 5,000).

This is my function:
std::string formatNumber(in t number)
{
// Convert the int to a string.
std::string numString = boost::lexical_ cast<std::strin g>(number);

std::string::co nst_reverse_ite rator i = numString.rbegi n(), end =
numString.rend( );
for (int j = 0; i != end; ++i, ++j)
{
// Add a comma every three places.
if (j < 3)
{
// ERROR HAPPENS ON THIS LINE BELOW.
i = numString.inser t(i + 1, ',');

Are you sure you can do +1 to the 'i'? Are you sure you can use the
*const* iterator for that? Just checking. Since your 'numString'
is not a constant object, why do you think you need a _const_ iterator
to work with it?

end = numString.rend( );

j = 0;
}
}

return numString;
}

I get an error saying it cannot convert from reverse_iterato r to
unsigned int. It looks to me as if it's trying to call the wrong
overloaded function, as I did a search on the method and I can indeed
pass an iterator and a char.

Can anybody tell me why this is failing?

Well, try to rewrite this using a non-const reverse iterator, or even
better, not using iterators at all. You know, you can just use
indices...

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Michael Coley]

I thought it would be something stupid.

Thanks to everyone who helped.

[Richard Herring]

In message <fa**********@n ews.datemas.de> , Victor Bazarov
<v.********@com Acast.netwrites

>Michael Coley wrote:

>Hi, I've wrote this function which should add a comma for every 3
digits in a number (so that it looks something like 5,000).

This is my function:
std::string formatNumber(in t number)
{
// Convert the int to a string.
std::string numString = boost::lexical_ cast<std::strin g>(number);

std::string::co nst_reverse_ite rator i = numString.rbegi n(), end =
numString.rend ();
for (int j = 0; i != end; ++i, ++j)
{
// Add a comma every three places.
if (j < 3)
{
// ERROR HAPPENS ON THIS LINE BELOW.
i = numString.inser t(i + 1, ',');

Are you sure you can do +1 to the 'i'? Are you sure you can use the
*const* iterator for that? Just checking.

No problem. The const describes what the iterator refers to, not the
iterator itself, and it models the random-access iterator concept, so
why not?

The real problem is elsewhere...

Since your 'numString'
is not a constant object, why do you think you need a _const_ iterator
to work with it?

> end = numString.rend( );

j = 0;
}
}

return numString;
}

I get an error saying it cannot convert from reverse_iterato r to
unsigned int. It looks to me as if it's trying to call the wrong
overloaded function, as I did a search on the method and I can indeed
pass an iterator and a char.

Can anybody tell me why this is failing?

Well, try to rewrite this using a non-const reverse iterator,

or better, a non-const non-reverse iterator :-/

>or even
better, not using iterators at all. You know, you can just use
indices...

Indeed.

--
Richard Herring

[Joe Greer]

Michael Coley <m1****@googlem ail.comwrote in news:1187868090 .229886.240180
@q3g2000prf.goo glegroups.com:

>
I get an error saying it cannot convert from reverse_iterato r to
unsigned int. It looks to me as if it's trying to call the wrong
overloaded function, as I did a search on the method and I can indeed
pass an iterator and a char.

Can anybody tell me why this is failing?

Because, while you can pass insert() an iterator and a character, you can't pass it a
reverse_iterato r and a char.

joe

[Jerry Coffin]

In article <11************ **********@q3g2 000prf.googlegr oups.com>,
m1****@googlema il.com says...

Hi, I've wrote this function which should add a comma for every 3
digits in a number (so that it looks something like 5,000).

iostreams can already format numbers like that without your doing all
the work:

First you create a numpunct facet to tell it how you want the formatting
done:

#include <locale>

template <class T>
struct formatter : std::numpunct<T {
protected:
T do_decimal_poin t() const { return T('.'); }
T do_thousands_se p() const { return T(','); }
std::basic_stri ng<Tdo_grouping () const {
return std::basic_stri ng<T>("\3");
}
};

Then you create a locale using that facet, and imbue a stream with the
locale to get it to use it:

std::locale f(std::locale:: classic(), new formatter<char> );
std::cout.imbue (f);

Then when you write numbers to that stream, they're formatted as you've
specified. If you really need to produce a string as the output, you can
imbue a stringstream with a locale as well.

Nicely enough, it's (usually) even easier to do the right thing, and
format the numbers the way the user expects:

std::locale local("");
std::cout.imbue (local);
std::cout << 123456789;

For me, this produces "123,456,78 9" -- but as (for example) a European
would typically configure their machine, it would produce "123.456.78 9"
instead, just as they expect.

--
Later,
Jerry.

The universe is a figment of its own imagination.