A question about the std::set<>::ite rator

[Renzr]

I have a problem about the std::set<>itera tor. After finding a term in
the std::set<>, i want to know the distance from
the current term to the begin(). But i have got a error. Please offer
me help, thank you. I am a freshman about the STL. The following is
the code.
#include <set>
#include <iostream>
#include <vector>
int main()
{
std::set<unsign ed inta;
a.insert(1); a.insert(2); a.insert(3); a.insert(4); a.insert(5);
std::set<unsign ed intb;
b.insert(6); b.insert(7); b.insert(8); b.insert(9); b.insert(10);
std::vector<std ::set<unsigned int ab(2);
ab[0]= a; ab[1]=b;
{
const unsigned int i=0, j=5;
std::set<unsign ed int>::iterator it=ab[i].find(5);
if(it!=ab[i].end()) std::cout<<it-ab[i].begin()<<std:: endl;
else { std::cout<"Ther e is no:"<<j<<" in "<<i<<std::endl ;
}
}
return 0;
}

This is the error:
error: no match for 'operator-' in 'it - (+(&ab)->std::vector<_T p,
_Alloc>::operat or[] [with _Tp = std::set<unsign ed int,
std::less<unsig ned int>, std::allocator< unsigned int, _Alloc =
std::allocator< std::set<unsign ed int, std::less<unsig ned int>,
std::allocator< unsigned int >](0u))->std::set<_Ke y, _Compare,
_Alloc>::begin [with _Key = unsigned int, _Compare =
std::less<unsig ned int>, _Alloc = std::allocator< unsigned int>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.2/../../../../include/c++/3.4.2/
bits/stl_bvector.h:1 80: note: candidates are: ptrdiff_t std::operator-
(const std::_Bit_itera tor_base&, const std::_Bit_itera tor_base&)

[Victor Bazarov]

Renzr wrote:

I have a problem about the std::set<>itera tor. After finding a term in
the std::set<>, i want to know the distance from
the current term to the begin(). But i have got a error. Please offer
me help, thank you. I am a freshman about the STL. The following is
the code.
#include <set>
#include <iostream>
#include <vector>
int main()
{
std::set<unsign ed inta;
a.insert(1); a.insert(2); a.insert(3); a.insert(4); a.insert(5);
std::set<unsign ed intb;
b.insert(6); b.insert(7); b.insert(8); b.insert(9); b.insert(10);
std::vector<std ::set<unsigned int ab(2);
ab[0]= a; ab[1]=b;
{
const unsigned int i=0, j=5;
std::set<unsign ed int>::iterator it=ab[i].find(5);
if(it!=ab[i].end()) std::cout<<it-ab[i].begin()<<std:: endl;

There is no operator - defined for it, that's what the compiler is
telling you. If you need to know how far it's from the start (though
I am not sure why you need that), use 'std::distance' function.

else { std::cout<"Ther e is no:"<<j<<" in "<<i<<std::endl ;
}
}
return 0;
}

This is the error:
error: no match for 'operator-' in 'it - (+(&ab)->std::vector<_T p,
_Alloc>::operat or[] [with _Tp = std::set<unsign ed int,
std::less<unsig ned int>, std::allocator< unsigned int, _Alloc =
std::allocator< std::set<unsign ed int, std::less<unsig ned int>,
std::allocator< unsigned int >](0u))->std::set<_Ke y, _Compare,
_Alloc>::begin [with _Key = unsigned int, _Compare =
std::less<unsig ned int>, _Alloc = std::allocator< unsigned int>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.2/../../../../include/c++/3.4.2/
bits/stl_bvector.h:1 80: note: candidates are: ptrdiff_t std::operator-
(const std::_Bit_itera tor_base&, const std::_Bit_itera tor_base&)

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

[Jonathan Lane]

The problem here is that there is no operator- for the iterator.

Take a look at the distance algorithm.

On Oct 3, 2:52 pm, Renzr <renzhengy...@g mail.comwrote:

I have a problem about the std::set<>itera tor. After finding a term in
the std::set<>, i want to know the distance from
the current term to the begin(). But i have got a error. Please offer
me help, thank you. I am a freshman about the STL. The following is
the code.
#include <set>
#include <iostream>
#include <vector>
int main()
{
std::set<unsign ed inta;
a.insert(1); a.insert(2); a.insert(3); a.insert(4); a.insert(5);
std::set<unsign ed intb;
b.insert(6); b.insert(7); b.insert(8); b.insert(9); b.insert(10);
std::vector<std ::set<unsigned int ab(2);
ab[0]= a; ab[1]=b;
{
const unsigned int i=0, j=5;
std::set<unsign ed int>::iterator it=ab[i].find(5);
if(it!=ab[i].end()) std::cout<<it-ab[i].begin()<<std:: endl;
else { std::cout<"Ther e is no:"<<j<<" in "<<i<<std::endl ;
}
}
return 0;

}

This is the error:
error: no match for 'operator-' in 'it - (+(&ab)->std::vector<_T p,
_Alloc>::operat or[] [with _Tp = std::set<unsign ed int,
std::less<unsig ned int>, std::allocator< unsigned int, _Alloc =
std::allocator< std::set<unsign ed int, std::less<unsig ned int>,
std::allocator< unsigned int >](0u))->std::set<_Ke y, _Compare,
_Alloc>::begin [with _Key = unsigned int, _Compare =
std::less<unsig ned int>, _Alloc = std::allocator< unsigned int>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.2/../../../../include/c++/3.4.2/
bits/stl_bvector.h:1 80: note: candidates are: ptrdiff_t std::operator-
(const std::_Bit_itera tor_base&, const std::_Bit_itera tor_base&)

[Renzr]

On Oct 3, 9:56 pm, "Victor Bazarov" <v.Abaza...@com Acast.netwrote:

Renzr wrote:

I have a problem about the std::set<>itera tor. After finding a term in
the std::set<>, i want to know the distance from
the current term to the begin(). But i have got a error. Please offer
me help, thank you. I am a freshman about the STL. The following is
the code.
#include <set>
#include <iostream>
#include <vector>
int main()
{
std::set<unsign ed inta;
a.insert(1); a.insert(2); a.insert(3); a.insert(4); a.insert(5);
std::set<unsign ed intb;
b.insert(6); b.insert(7); b.insert(8); b.insert(9); b.insert(10);
std::vector<std ::set<unsigned int ab(2);
ab[0]= a; ab[1]=b;
{
const unsigned int i=0, j=5;
std::set<unsign ed int>::iterator it=ab[i].find(5);
if(it!=ab[i].end()) std::cout<<it-ab[i].begin()<<std:: endl;

There is no operator - defined for it, that's what the compiler is
telling you. If you need to know how far it's from the start (though
I am not sure why you need that), use 'std::distance' function.

else { std::cout<"Ther e is no:"<<j<<" in "<<i<<std::endl ;
}
}
return 0;
}

This is the error:
error: no match for 'operator-' in 'it - (+(&ab)->std::vector<_T p,
_Alloc>::operat or[] [with _Tp = std::set<unsign ed int,
std::less<unsig ned int>, std::allocator< unsigned int, _Alloc =
std::allocator< std::set<unsign ed int, std::less<unsig ned int>,
std::allocator< unsigned int >](0u))->std::set<_Ke y, _Compare,
_Alloc>::begin [with _Key = unsigned int, _Compare =
std::less<unsig ned int>, _Alloc = std::allocator< unsigned int>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.2/../../../../include/c++/3.4.2/
bits/stl_bvector.h:1 80: note: candidates are: ptrdiff_t std::operator-
(const std::_Bit_itera tor_base&, const std::_Bit_itera tor_base&)

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

Thanks for your solution.
The resean is in my FEM code, I want to get the local position of DOF
in the ith row.
So i design the std::vector<std ::set<unsigned int.
Maybe std::vector<std ::vector<unsign ed int is prefered.
In my loop to ith row (std::vector[i]), several "unsigned int" will be
added into std::vector[i].
And i need the sorted "unsigned int" in std::vector[i]. So, I have two
ways.
The first is to design the std::vector[i] as std::vector<uns igned
int>. But this way we should involve in std::sort() on
std::vector<uns igned int>. The second way is to design the
std::vector[i] as std::set<unsign ed int>.
In the second way, when I need get the [j]th value in std::vector[i]--

>std::set<>, it is not easy like std::vector<>.

And also, to get the local postion of value T in std::set<unsign ed
intof std::vector[i] is also not easy like std::vector<>.
That is my problem.
So, I have two questions.
1st, Why not std::set<offer operator [i], where i is the local
index?
2nd, Why not std::set<>::ite rator is invalid in "iterator- begin()"?

[Victor Bazarov]

Renzr wrote:

[..] I have two questions.
1st, Why not std::set<offer operator [i], where i is the local
index?

Because 'std::set' is not a sequential container. Only sequences
are required to provide indexing.

2nd, Why not std::set<>::ite rator is invalid in "iterator- begin()"?

Because it's not a random-access iterator. It's a bidirectional
iterator that is not required to provide the subtraction operator.

You need to decide on what container to use based on which part of
its functionality you use the most. If it's insertion and iteration,
and rarely getting the "index", 'std::set' would do nicely. If you
insert rarely (or only once), and then you need to index within the
container the rest of its life, you might be better off with the
vector, as you pointed out. Yes, you need it sorted, but that's
not as expensive as you might think. If you know the maximum # of
DOF, you can reserve a certain size in your vectors to prevent
reallocations when inserting.

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

[=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?=]

On 2007-10-03 16:12, Renzr wrote:

On Oct 3, 9:56 pm, "Victor Bazarov" <v.Abaza...@com Acast.netwrote:

>Renzr wrote:

I have a problem about the std::set<>itera tor. After finding a term in
the std::set<>, i want to know the distance from
the current term to the begin(). But i have got a error. Please offer
me help, thank you. I am a freshman about the STL. The following is
the code.
#include <set>
#include <iostream>
#include <vector>
int main()
{
std::set<unsign ed inta;
a.insert(1); a.insert(2); a.insert(3); a.insert(4); a.insert(5);
std::set<unsign ed intb;
b.insert(6); b.insert(7); b.insert(8); b.insert(9); b.insert(10);
std::vector<std ::set<unsigned int ab(2);
ab[0]= a; ab[1]=b;
{
const unsigned int i=0, j=5;
std::set<unsign ed int>::iterator it=ab[i].find(5);
if(it!=ab[i].end()) std::cout<<it-ab[i].begin()<<std:: endl;

There is no operator - defined for it, that's what the compiler is
telling you. If you need to know how far it's from the start (though
I am not sure why you need that), use 'std::distance' function.

else { std::cout<"Ther e is no:"<<j<<" in "<<i<<std::endl ;
}
}
return 0;
}

This is the error:
error: no match for 'operator-' in 'it - (+(&ab)->std::vector<_T p,
_Alloc>::operat or[] [with _Tp = std::set<unsign ed int,
std::less<unsig ned int>, std::allocator< unsigned int, _Alloc =
std::allocator< std::set<unsign ed int, std::less<unsig ned int>,
std::allocator< unsigned int >](0u))->std::set<_Ke y, _Compare,
_Alloc>::begin [with _Key = unsigned int, _Compare =
std::less<unsig ned int>, _Alloc = std::allocator< unsigned int>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.2/../../../../include/c++/3.4.2/
bits/stl_bvector.h:1 80: note: candidates are: ptrdiff_t std::operator-
(const std::_Bit_itera tor_base&, const std::_Bit_itera tor_base&)

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

Thanks for your solution.
The resean is in my FEM code, I want to get the local position of DOF
in the ith row.
So i design the std::vector<std ::set<unsigned int.
Maybe std::vector<std ::vector<unsign ed int is prefered.
In my loop to ith row (std::vector[i]), several "unsigned int" will be
added into std::vector[i].
And i need the sorted "unsigned int" in std::vector[i]. So, I have two
ways.
The first is to design the std::vector[i] as std::vector<uns igned
int>. But this way we should involve in std::sort() on
std::vector<uns igned int>. The second way is to design the
std::vector[i] as std::set<unsign ed int>.

Actually, it is probably cheaper to insert the elements in the vector
and then sort it that it is to insert them into the set. For large
number of elements the difference can be quite noticeable.

--
Erik Wikström

[Renzr]

On Oct 3, 10:21 pm, "Victor Bazarov" <v.Abaza...@com Acast.netwrote:

Renzr wrote:

[..] I have two questions.
1st, Why not std::set<offer operator [i], where i is the local
index?

Because 'std::set' is not a sequential container. Only sequences
are required to provide indexing.

2nd, Why not std::set<>::ite rator is invalid in "iterator- begin()"?

Because it's not a random-access iterator. It's a bidirectional
iterator that is not required to provide the subtraction operator.

You need to decide on what container to use based on which part of
its functionality you use the most. If it's insertion and iteration,
and rarely getting the "index", 'std::set' would do nicely. If you
insert rarely (or only once), and then you need to index within the
container the rest of its life, you might be better off with the
vector, as you pointed out. Yes, you need it sorted, but that's
not as expensive as you might think. If you know the maximum # of
DOF, you can reserve a certain size in your vectors to prevent
reallocations when inserting.

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

Thanks for your solution again. I think I have got you.
In my code, the std::vector<std ::set<unsigned int is adopted as the
sparse pattenr of the finite-element mesh.
So to the ith row, its relative DOFs are only inserted once, and it
will be used in the assemble frequently.
Yes, I know the maximun # of DOF. And from you, I will chose the
std::vector<>:: reserce() to pre-allocate space.
Your solution is perfect.
I will adopte the std::vector<std ::vector<unsign ed int.
And the std::sort(std:: vector<>:iterat or, std::vector<>:: iteraotr) is
not expensive only more.
:) Thanks.
Best regards,
Ren ZhengYong

[Renzr]

On Oct 3, 10:35 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-10-03 16:12, Renzr wrote:

On Oct 3, 9:56 pm, "Victor Bazarov" <v.Abaza...@com Acast.netwrote:

Renzr wrote:
I have a problem about the std::set<>itera tor. After finding a term in
the std::set<>, i want to know the distance from
the current term to the begin(). But i have got a error. Please offer
me help, thank you. I am a freshman about the STL. The following is
the code.
#include <set>
#include <iostream>
#include <vector>
int main()
{
std::set<unsign ed inta;
a.insert(1); a.insert(2); a.insert(3); a.insert(4); a.insert(5);
std::set<unsign ed intb;
b.insert(6); b.insert(7); b.insert(8); b.insert(9); b.insert(10);
std::vector<std ::set<unsigned int ab(2);
ab[0]= a; ab[1]=b;
{
const unsigned int i=0, j=5;
std::set<unsign ed int>::iterator it=ab[i].find(5);
if(it!=ab[i].end()) std::cout<<it-ab[i].begin()<<std:: endl;

There is no operator - defined for it, that's what the compiler is
telling you. If you need to know how far it's from the start (though
I am not sure why you need that), use 'std::distance' function.

else { std::cout<"Ther e is no:"<<j<<" in "<<i<<std::endl ;
}
}
return 0;
}

This is the error:
error: no match for 'operator-' in 'it - (+(&ab)->std::vector<_T p,
_Alloc>::operat or[] [with _Tp = std::set<unsign ed int,
std::less<unsig ned int>, std::allocator< unsigned int, _Alloc =
std::allocator< std::set<unsign ed int, std::less<unsig ned int>,
std::allocator< unsigned int >](0u))->std::set<_Ke y, _Compare,
_Alloc>::begin [with _Key = unsigned int, _Compare =
std::less<unsig ned int>, _Alloc = std::allocator< unsigned int>]()'
/usr/lib/gcc/i386-redhat-linux/3.4.2/../../../../include/c++/3.4.2/
bits/stl_bvector.h:1 80: note: candidates are: ptrdiff_t std::operator-
(const std::_Bit_itera tor_base&, const std::_Bit_itera tor_base&)

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

Thanks for your solution.
The resean is in my FEM code, I want to get the local position of DOF
in the ith row.
So i design the std::vector<std ::set<unsigned int.
Maybe std::vector<std ::vector<unsign ed int is prefered.
In my loop to ith row (std::vector[i]), several "unsigned int" will be
added into std::vector[i].
And i need the sorted "unsigned int" in std::vector[i]. So, I have two
ways.
The first is to design the std::vector[i] as std::vector<uns igned
int>. But this way we should involve in std::sort() on
std::vector<uns igned int>. The second way is to design the
std::vector[i] as std::set<unsign ed int>.

Actually, it is probably cheaper to insert the elements in the vector
and then sort it that it is to insert them into the set. For large
number of elements the difference can be quite noticeable.

--
Erik Wikström

Thanks for your solution.
Your help offer me a right choice on the std::vector<and std::set<>