1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two iterators:
"it_p" and "it_q". When I print "first" and "second" I get 1 and 4. But
should:
int second = *myset.end();
not return the value of the element *after* the last which is undefined?
I thought that I had to decrement myset.end() by one to get the value 4.
2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators while set supports
bidirectional iterators.
But where (have tried) google do I find a list of each iterator that a
container supports?
18  2095 
desktop wrote:
1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
This causes undefined behaviour. The iterator returned by 'end()' is
non-dereferenceable . You probably want '*myset.rbegin( )'.
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two
iterators: "it_p" and "it_q". When I print "first" and "second" I get
1 and 4. But should:
int second = *myset.end();
not return the value of the element *after* the last which is
undefined? I thought that I had to decrement myset.end() by one to
get the value 4.
Whatever you think your program should do, it's all wrong. The code
has undefined behaviour.
2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators
Wrong. std::list supports bidirectional iterators.
while set supports
bidirectional iterators.
But where (have tried) google do I find a list of each iterator that a
container supports?
Get a copy of the Standard.
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask
Victor Bazarov wrote:
desktop wrote:
>1)
I have this code:
std::list<intm ylist;
mylist.push_ba ck(1);
mylist.push_ba ck(2);
mylist.push_ba ck(3);
mylist.push_ba ck(4);
std::list<int> ::iterator it_p = mylist.begin();
std::list<int> ::iterator it_q = mylist.end();
std::set<intmy set(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
This causes undefined behaviour. The iterator returned by 'end()' is
non-dereferenceable . You probably want '*myset.rbegin( )'.
>std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two
iterators: "it_p" and "it_q". When I print "first" and "second" I get
1 and 4. But should:
int second = *myset.end();
not return the value of the element *after* the last which is
undefined? I thought that I had to decrement myset.end() by one to
get the value 4.
Whatever you think your program should do, it's all wrong. The code
has undefined behaviour.
>2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators
Wrong. std::list supports bidirectional iterators.
Ok in the standard it says that list, vector and dequeue all are
Sequences. On page 469 it says that iterator should at least be forward.
But since binary minus '-' gives a compile error I assume they don't
support random access iterator. Is the *at least* formulation not a bit
un-precise?
Further the i and j iterators has to be of type input iterator. I don't
know of any containers that supports this type or any way that you can
make an input iterator.
Is it to make restrictions on the use of these iterators if they are
used in the eg. constructor (you are only allowed to use the operators
for input iterators even though no containers return this kind of iterator)?
desktop napsal:
1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two iterators:
"it_p" and "it_q". When I print "first" and "second" I get 1 and 4. But
should:
int second = *myset.end();
not return the value of the element *after* the last which is undefined?
I thought that I had to decrement myset.end() by one to get the value 4.
Yes, you have to do it. The code you've posted just invokes undefined
behaviour,
which means that it can result to anything the implementor decides,
particularly, it can return 4, but on a different platform, it might
crash the
program or return -45246961 or whatever else.
2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators while set supports
bidirectional iterators.
But where (have tried) google do I find a list of each iterator that a
container supports?
Each container has a specific iterator class. This class satisfies
some
concept (similar to interface), theses are the Input/Forward/
Bidirectional/...
[btw. there is a hierarchy between these]. What each container's
iterator has
to satisfy, can be read in the SGI STL manual. For example, with list,
there is
list is a model of reversible container
and on a page about reversible container, there is
.... the iterators must be Bidirectional Iterators
so we know a list must hav an iterator at least as strong as
Bidirectional.
Regards
Jiri Palecek
desktop <ff*@sss.comwro te in news:f4******** **@news.net.uni-c.dk:
1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
Undefined behaviour. You cannot dereference an end() iterator.
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two
iterators:
"it_p" and "it_q". When I print "first" and "second" I get 1 and 4. But
should:
int second = *myset.end();
not return the value of the element *after* the last which is
undefined?
I thought that I had to decrement myset.end() by one to get the value
4.
Undefined behaviour has been invoked. One can no longer predict the
behaviour.
desktop napsal:
Victor Bazarov wrote:
desktop wrote:
1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
This causes undefined behaviour. The iterator returned by 'end()' is
non-dereferenceable . You probably want '*myset.rbegin( )'.
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two
iterators: "it_p" and "it_q". When I print "first" and "second" I get
1 and 4. But should:
int second = *myset.end();
not return the value of the element *after* the last which is
undefined? I thought that I had to decrement myset.end() by one to
get the value 4.
Whatever you think your program should do, it's all wrong. The code
has undefined behaviour.
2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators
Wrong. std::list supports bidirectional iterators.
Ok in the standard it says that list, vector and dequeue all are
Sequences. On page 469 it says that iterator should at least be forward.
But since binary minus '-' gives a compile error I assume they don't
support random access iterator. Is the *at least* formulation not a bit
un-precise?
Did you get compile time error on list, deque or vector? list only
has
bidirectional iterator, whereas deque and vector are Random Access
Containers which support random access iterators.
>
Further the i and j iterators has to be of type input iterator. I don't
know of any containers that supports this type or any way that you can
make an input iterator.
Virtually any iterator you can make is input iterator. For example,
forward
iterator is a refinement of input iterator. So any iterator of any
container
will do. There are also "pure" input iterators like istream_iterato r.
Is it to make restrictions on the use of these iterators if they are
used in the eg. constructor (you are only allowed to use the operators
for input iterators even though no containers return this kind of iterator)?
Yes. This means you can use istream_iterato r in the constructor as
well.
Regards
Jiri Palecek jp******@web.de wrote:
desktop napsal:
>1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two iterators:
"it_p" and "it_q". When I print "first" and "second" I get 1 and 4. But
should:
int second = *myset.end();
not return the value of the element *after* the last which is undefined?
I thought that I had to decrement myset.end() by one to get the value 4.
Yes, you have to do it. The code you've posted just invokes undefined
behaviour,
which means that it can result to anything the implementor decides,
particularly, it can return 4, but on a different platform, it might
crash the
program or return -45246961 or whatever else.
>2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators while set supports
bidirectiona l iterators.
But where (have tried) google do I find a list of each iterator that a
container supports?
Each container has a specific iterator class. This class satisfies
some
concept (similar to interface), theses are the Input/Forward/
Bidirectional/...
[btw. there is a hierarchy between these]. What each container's
iterator has
to satisfy, can be read in the SGI STL manual. For example, with list,
there is
list is a model of reversible container
and on a page about reversible container, there is
.... the iterators must be Bidirectional Iterators
so we know a list must hav an iterator at least as strong as
Bidirectional.
Actually the C++ Standard says that i should be at least be forward see
page 469 item [5]: http://www.usatlas.bnl.gov/~dladams/...14882-2003.pdf jp******@web.de wrote:
desktop napsal:
>Victor Bazarov wrote:
>>desktop wrote:
1)
I have this code:
std::list<in tmylist;
mylist.push_ back(1);
mylist.push_ back(2);
mylist.push_ back(3);
mylist.push_ back(4);
std::list<in t>::iterator it_p = mylist.begin();
std::list<in t>::iterator it_q = mylist.end();
std::set<int myset(it_p,it_q );
int first = *myset.begin();
int second = *myset.end();
This causes undefined behaviour. The iterator returned by 'end()' is
non-dereferenceable . You probably want '*myset.rbegin( )'.
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two
iterators: "it_p" and "it_q". When I print "first" and "second" I get
1 and 4. But should:
int second = *myset.end();
not return the value of the element *after* the last which is
undefined? I thought that I had to decrement myset.end() by one to
get the value 4.
Whatever you think your program should do, it's all wrong. The code
has undefined behaviour.
2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators
Wrong. std::list supports bidirectional iterators.
Ok in the standard it says that list, vector and dequeue all are
Sequences. On page 469 it says that iterator should at least be forward.
But since binary minus '-' gives a compile error I assume they don't
support random access iterator. Is the *at least* formulation not a bit
un-precise?
Did you get compile time error on list, deque or vector? list only
has
bidirectional iterator, whereas deque and vector are Random Access
Containers which support random access iterators.
>Further the i and j iterators has to be of type input iterator. I don't
know of any containers that supports this type or any way that you can
make an input iterator.
Virtually any iterator you can make is input iterator. For example,
forward
iterator is a refinement of input iterator. So any iterator of any
container
will do. There are also "pure" input iterators like istream_iterato r.
>Is it to make restrictions on the use of these iterators if they are
used in the eg. constructor (you are only allowed to use the operators
for input iterators even though no containers return this kind of iterator)?
Yes. This means you can use istream_iterato r in the constructor as
well.
What confuses me if its allowed use other operators on i and j besides
from the input iterator operations.
If I pass two vector iterators (random access) as i and j they fulfill
input operators but also some extra. Is it allowed use these extra
operators or is it only legal to use input defined ones?
desktop napsal:
jp******@web.de wrote:
desktop napsal:
1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two iterators:
"it_p" and "it_q". When I print "first" and "second" I get 1 and 4. But
should:
int second = *myset.end();
not return the value of the element *after* the last which is undefined?
I thought that I had to decrement myset.end() by one to get the value 4.
Yes, you have to do it. The code you've posted just invokes undefined
behaviour,
which means that it can result to anything the implementor decides,
particularly, it can return 4, but on a different platform, it might
crash the
program or return -45246961 or whatever else.
2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators while set supports
bidirectional iterators.
But where (have tried) google do I find a list of each iterator that a
container supports?
Each container has a specific iterator class. This class satisfies
some
concept (similar to interface), theses are the Input/Forward/
Bidirectional/...
[btw. there is a hierarchy between these]. What each container's
iterator has
to satisfy, can be read in the SGI STL manual. For example, with list,
there is
list is a model of reversible container
and on a page about reversible container, there is
.... the iterators must be Bidirectional Iterators
so we know a list must hav an iterator at least as strong as
Bidirectional.
Actually the C++ Standard says that i should be at least be forward see
page 469 item [5]:
http://www.usatlas.bnl.gov/~dladams/...14882-2003.pdf
Yes, but in 23.2.2 item [2], on page 481, there is
A list satisfies all requirements ... of reversible container.
And in 23.1 item 9, there is that reversible containers have
Bidirectional or
Random Access category iterators. Because Random Access are stronger
than Bidirectional and Bidirectional are stronger than Forward (24.1),
we know that
a list have at leas as strong iterators as Bidirectional. jp******@web.de wrote:
desktop napsal:
>jp******@web.de wrote:
>>desktop napsal:
1)
I have this code:
std::list<intmy list;
mylist.push_bac k(1);
mylist.push_bac k(2);
mylist.push_bac k(3);
mylist.push_bac k(4);
std::list<int>: :iterator it_p = mylist.begin();
std::list<int>: :iterator it_q = mylist.end();
std::set<intmys et(it_p,it_q);
int first = *myset.begin();
int second = *myset.end();
std::cout << "first = " << first << std::endl;
std::cout << "second = " << second << std::endl;
I copy the elements from the "list" to the "set" with the two iterators:
"it_p" and "it_q". When I print "first" and "second" I get 1 and 4. But
should:
int second = *myset.end();
not return the value of the element *after* the last which is undefined?
I thought that I had to decrement myset.end() by one to get the value 4.
Yes, you have to do it. The code you've posted just invokes undefined
behaviour,
which means that it can result to anything the implementor decides,
particularl y, it can return 4, but on a different platform, it might
crash the
program or return -45246961 or whatever else.
2)
Another thing. As I understand each container supports a specific
iterator. Eg. list only supports forward iterators while set supports
bidirectiona l iterators.
But where (have tried) google do I find a list of each iterator that a
container supports?
Each container has a specific iterator class. This class satisfies
some
concept (similar to interface), theses are the Input/Forward/
Bidirection al/...
[btw. there is a hierarchy between these]. What each container's
iterator has
to satisfy, can be read in the SGI STL manual. For example, with list,
there is
list is a model of reversible container
and on a page about reversible container, there is
.... the iterators must be Bidirectional Iterators
so we know a list must hav an iterator at least as strong as
Bidirectional .
Actually the C++ Standard says that i should be at least be forward see
page 469 item [5]:
http://www.usatlas.bnl.gov/~dladams/...14882-2003.pdf
Yes, but in 23.2.2 item [2], on page 481, there is
A list satisfies all requirements ... of reversible container.
And in 23.1 item 9, there is that reversible containers have
Bidirectional or
Random Access category iterators. Because Random Access are stronger
than Bidirectional and Bidirectional are stronger than Forward (24.1),
we know that
a list have at leas as strong iterators as Bidirectional.
Ok I guess what I was referring to was for Sequences which is the
"general abstraction" and not list which is a "concrete" realization. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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