«

Can I define an iterator for an object of a standard container class
without using the concrete type of that container object?

I tried things like

1 #include <list>
2 void foo(std::list<int> ilist) {
3 ilist.iterator it;
4 for (it = ilist.begin(); it != ilist.end(); ++it) { *it; }
5 }

and

1 #include <list>
2 void foo(std::list<int> ilist) {
3 typeof(ilist)::iterator it;
4 for (it = ilist.begin(); it != ilist.end(); ++it) { *it; }
5 }

For the first code I get

foo.cc:3:11: error: invalid use of 'std::list<int>::iterator'

so at least ilist.iterator seems indeed to be understood as
std::list<int>::iterator. In the second case I get

foo.cc:3:29: error: expected initializer before 'it'

Is there a way to define the iterator without using std::list<int>::iterator
explicitly?

urs

On 09/15/11 09:51 AM, Urs Thuermann wrote:
> Can I define an iterator for an object of a standard container class
> without using the concrete type of that container object?
>
> I tried things like
>
> 1 #include<list>
> 2 void foo(std::list<int> ilist) {
> 3 ilist.iterator it;
> 4 for (it = ilist.begin(); it != ilist.end(); ++it) { *it; }
> 5 }
>
> and
>
> 1 #include<list>
> 2 void foo(std::list<int> ilist) {
> 3 typeof(ilist)::iterator it;
> 4 for (it = ilist.begin(); it != ilist.end(); ++it) { *it; }
> 5 }
>
> For the first code I get
>
> foo.cc:3:11: error: invalid use of 'std::list<int>::iterator'
>
> so at least ilist.iterator seems indeed to be understood as
> std::list<int>::iterator. In the second case I get
>
> foo.cc:3:29: error: expected initializer before 'it'
>
> Is there a way to define the iterator without using std::list<int>::iterator
> explicitly?

Only if your compiler supports the new auto keyword. Otherwise use a
typedef for the parameter type.

--
Ian Collins

Ian Collins <ian-> wrote:
> Only if your compiler supports the new auto keyword. Otherwise use a
> typedef for the parameter type.

Would decltype(container)::iterator work in C++0x?

Juha Nieminen wrote:

> Ian Collins <ian-> wrote:
>> Only if your compiler supports the new auto keyword. Otherwise use a
>> typedef for the parameter type.
>
> Would decltype(container)::iterator work in C++0x?

C++11 now. Yes, but it would be easier to just write:
auto it=ilist.begin();

Marc <> writes:

> Juha Nieminen wrote:
>
> > Ian Collins <ian-> wrote:
> >> Only if your compiler supports the new auto keyword. Otherwise use a
> >> typedef for the parameter type.
> >
> > Would decltype(container)::iterator work in C++0x?
>
> C++11 now. Yes, but it would be easier to just write:
> auto it=ilist.begin();

Ok, that looks nice and GCC already supports it. Is it also possible
to define a const_iterator from a non-const container object using the
auto keyword, i.e. a list<T>::const_iterator from an object of type
list<T>?

urs

Urs Thuermann wrote:

> Marc <> writes:
>
>> Juha Nieminen wrote:
>>
>> > Ian Collins <ian-> wrote:
>> >> Only if your compiler supports the new auto keyword. Otherwise use a
>> >> typedef for the parameter type.
>> >
>> > Would decltype(container)::iterator work in C++0x?
>>
>> C++11 now. Yes, but it would be easier to just write:
>> auto it=ilist.begin();
>
> Ok, that looks nice and GCC already supports it. Is it also possible
> to define a const_iterator from a non-const container object using the
> auto keyword, i.e. a list<T>::const_iterator from an object of type
> list<T>?

Yes, call cbegin instead of begin ('c' for "const").

Marc <> writes:

> > Ok, that looks nice and GCC already supports it. Is it also possible
> > to define a const_iterator from a non-const container object using the
> > auto keyword, i.e. a list<T>::const_iterator from an object of type
> > list<T>?
>
> Yes, call cbegin instead of begin ('c' for "const").

Ah, thanks. Haven't seen that before. Now I changed some of the code
I currently work on and it looks so much cleaner. Thanks again.

urs