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Senthilvel
Guest
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 Posted: Mon Jun 28, 2004 8:14 am Post subject: Template Specialization |
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Hi folks,
I was trying to learn the standard library algorithms where i got stuck with
the templates.
I wrote one function to eliminate the duplicates(from The C++ Programming
Language 3rd Edition)
template<class Con> void RemoveDuplicates(Con& seq)
{
sort(seq.begin(),seq.end());
typename Con::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
int main()
{
vector<int> ls1;
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
print_all(ls1,cout);
RemoveDuplicates(ls1);
print_all(ls1,cout);
return 0;
}
This worked fine for vector,deque but failed for list as sort needs randon
access iterators which is not provided by list
So i thought of specializing the function for list, but how do i do it ???
List needs a template argument and i do not know how to pass that
template argument.I did this way
template<class T> void RemoveDuplicates(list<T> & seq)
{
seq.sort();
typename list<T>::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
int main()
{
list<int> ls1;
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
print_all(ls1,cout);
RemoveDuplicates<int>(ls1);
print_all(ls1,cout);
return 0;
}
Now i explicity need to specify the type in the RemoveDuplicates function.
Am i correct or am i missing something ???
Thanks and Best Regards,
Senthilvel.
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Sumit Rajan
Guest
|
| Posted: Mon Jun 28, 2004 8:55 am Post subject: Re: Template Specialization |
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"Senthilvel" <Senthil (AT) nospam (DOT) com> wrote
| Quote: | Hi folks,
I was trying to learn the standard library algorithms where i got stuck
with
the templates.
I wrote one function to eliminate the duplicates(from The C++ Programming
Language 3rd Edition)
template<class Con> void RemoveDuplicates(Con& seq)
{
sort(seq.begin(),seq.end());
typename Con::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
int main()
{
vector<int> ls1;
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
print_all(ls1,cout);
RemoveDuplicates(ls1);
print_all(ls1,cout);
return 0;
}
This worked fine for vector,deque but failed for list as sort needs randon
access iterators which is not provided by list
So i thought of specializing the function for list, but how do i do it ???
List needs a template argument and i do not know how to pass that
template argument.I did this way
template<class T> void RemoveDuplicates(list<T> & seq)
{
seq.sort();
typename list<T>::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
int main()
{
list<int> ls1;
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
print_all(ls1,cout);
RemoveDuplicates<int>(ls1);
print_all(ls1,cout);
return 0;
}
Now i explicity need to specify the type in the RemoveDuplicates function.
Am i correct or am i missing something ???
Thanks and Best Regards,
Senthilvel.
|
You could try something like this:
#include <iostream>
#include <vector>
#include <algorithm>
#include <list>
template<class Con> void RemoveDuplicates(Con& seq)
{
std::sort(seq.begin(),seq.end());
typename Con::iterator p = std::unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
template<class T> void RemoveDuplicates (std::list<T>& lst)
{
lst.sort();
typename std::list<T>::iterator p = std::unique(lst.begin(),lst.end());
lst.erase(p,lst.end());
}
int main()
{
std::list<int> ls1;
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
std::copy(ls1.begin(),ls1.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << 'n';
RemoveDuplicates(ls1);
std::copy(ls1.begin(),ls1.end(),
std::ostream_iterator
std::cout << 'n';
}
Regards,
Sumit.
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Senthilvel
Guest
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| Posted: Mon Jun 28, 2004 9:33 am Post subject: Re: Template Specialization |
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------> By Senthil
| Quote: |
template<class Con> void RemoveDuplicates(Con& seq)
{
sort(seq.begin(),seq.end());
typename Con::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
template<class T> void RemoveDuplicates(list<T> & seq)
{
seq.sort();
typename list<T>::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
|
------> By Sumit
| Quote: | template<class Con> void RemoveDuplicates(Con& seq)
{
std::sort(seq.begin(),seq.end());
typename Con::iterator p = std::unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
template<class T> void RemoveDuplicates (std::list<T>& lst)
{
lst.sort();
typename std::list<T>::iterator p =
std::unique(lst.begin(),lst.end());
lst.erase(p,lst.end());
}
|
Thats exacty what i have done Sumit...
I get the error
"error C2667: 'RemoveDuplicates' : none of 2 overload have a best
conversion"
"error C2668: 'RemoveDuplicates' : ambiguous call to overloaded function"
on the line
RemoveDuplicates(ls1);
in main
BTW..I am using MS -VC++ 6 compiler ..
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Sumit Rajan
Guest
|
| Posted: Mon Jun 28, 2004 9:33 am Post subject: Re: Template Specialization |
|
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"Senthilvel" <Senthil (AT) nospam (DOT) com> wrote
| Quote: | BTW..I am using MS -VC++ 6 compiler ..
|
Well, it compiles using VC++ 7.1 and Comeau C++ 4.3.3. I guess it
VC++ 6.0 does not extend full support to overloading templates (but I'm not
sure as I have never used 6.0).
Regards,
Sumit.
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Alf P. Steinbach
Guest
|
| Posted: Mon Jun 28, 2004 10:01 am Post subject: Re: Template Specialization |
|
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* Senthilvel:
| Quote: |
template<class Con> void RemoveDuplicates(Con& seq)
{
sort(seq.begin(),seq.end());
typename Con::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
int main()
{
vector<int> ls1;
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
print_all(ls1,cout);
RemoveDuplicates(ls1);
print_all(ls1,cout);
return 0;
}
This worked fine for vector,deque but failed for list as sort needs randon
access iterators which is not provided by list
So i thought of specializing the function for list, but how do i do it ???
List needs a template argument and i do not know how to pass that
template argument.I did this way
template<class T> void RemoveDuplicates(list<T> & seq)
{
seq.sort();
typename list<T>::iterator p = unique(seq.begin(),seq.end());
seq.erase(p,seq.end());
}
int main()
{
list<int> ls1;
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
ls1.push_back(1);
ls1.push_back(2);
ls1.push_back(3);
ls1.push_back(4);
print_all(ls1,cout);
RemoveDuplicates<int>(ls1);
print_all(ls1,cout);
return 0;
}
Now i explicity need to specify the type in the RemoveDuplicates function.
Am i correct or am i missing something ???
|
No, you don't need to specify the type, it's inferred.
But your implementation is tied specifically to std::list.
It's generally better to separate the template requirements, e.g. like
#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
template< class T >
struct HasRandomIterators_{ enum{ yes = true }; };
template< typename T >
struct HasRandomIterators_< std::list{ enum{ yes = false }; };
template< class Container, bool genericIsOK = true>
struct RemoveDuplicates_
{
static void from( Container& c )
{
std::sort( c.begin(), c.end() );
typename Container::iterator it = std::unique( c.begin(),
c.end() );
c.erase( it, c.end() );
}
};
template< class Container>
struct RemoveDuplicates_<Container, false>
{
static void from( Container& c )
{
c.sort();
c.unique();
}
};
template< class Container >
void removeDuplicates( Container& c )
{
RemoveDuplicates_<Container,
HasRandomIterators_::from( c );
}
template< class Container >
void printAll( Container const& c )
{
typedef Container::const_iterator Iterator;
for( Iterator it = c.begin(); it != c.end(); ++it )
{
std::cout << *it << std::endl;
}
}
int main()
{
std::list
c.push_back( 1 );
c.push_back( 2 );
c.push_back( 3 );
c.push_back( 4 );
c.push_back( 1 );
c.push_back( 2 );
c.push_back( 3 );
c.push_back( 4 );
printAll( c );
std::cout << std::endl;
removeDuplicates( c );
printAll( c );
}
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
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Senthilvel
Guest
|
| Posted: Mon Jun 28, 2004 10:18 am Post subject: Re: Template Specialization |
|
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| Quote: | No, you don't need to specify the type, it's inferred.
But your implementation is tied specifically to std::list.
It's generally better to separate the template requirements, e.g. like
#include <iostream
#include
#include
#include
template< class T
struct HasRandomIterators_{ enum{ yes = true }; };
template< typename T
struct HasRandomIterators_< std::list{ enum{ yes = false }; };
template< class Container, bool genericIsOK = true
struct RemoveDuplicates_
{
static void from( Container& c )
{
std::sort( c.begin(), c.end() );
typename Container::iterator it = std::unique( c.begin(),
c.end() );
c.erase( it, c.end() );
}
};
template< class Container
struct RemoveDuplicates_
{
static void from( Container& c )
{
c.sort();
c.unique();
}
};
template< class Container
void removeDuplicates( Container& c )
{
RemoveDuplicates_
HasRandomIterators_::from( c );
}
template< class Container
void printAll( Container const& c )
{
typedef Container::const_iterator Iterator;
for( Iterator it = c.begin(); it != c.end(); ++it )
{
std::cout << *it << std::endl;
}
}
|
Thanks Alf...Thats a nice technique...
But my only problem it does not compile on VC++ 6.0 : - (
error C2989: 'HasRandomIterators_
| Quote: | ' : template class has already been defined as a non-template class
error C2988: unrecognizable template declaration/definition |
error C2989: 'RemoveDuplicates_<Container,0>' : template class has already
been defined as a non-template class
error C2988: unrecognizable template declaration/definition
Got to keep this in mind until we move to VC 7.0..(Hoping this code compiles
will compile in that version )
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John Harrison
Guest
|
| Posted: Mon Jun 28, 2004 12:29 pm Post subject: Re: Template Specialization |
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| Quote: | Thanks Alf...Thats a nice technique...
But my only problem it does not compile on VC++ 6.0 : - (
error C2989: 'HasRandomIterators_<class std::list
std::allocator
' : template class has already been defined as a non-template class
error C2988: unrecognizable template declaration/definition
error C2989: 'RemoveDuplicates_
been defined as a non-template class
error C2988: unrecognizable template declaration/definition
Got to keep this in mind until we move to VC 7.0..(Hoping this code
compiles
will compile in that version )
|
Alf was using partial template specialisation, which is not supported in
VC++ 6. I would leave off learning templates until you upgrade to VC++ 7.1
(not 7.0), VC++ 6 template support is poor and you'll only end up learning
stuff which isn't true.
John
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red floyd
Guest
|
| Posted: Mon Jun 28, 2004 5:06 pm Post subject: Re: Template Specialization |
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Senthilvel wrote:
Your problem is MSVC6. VC6 is widely known (and acknowledged by MS) to
have problems with template specializations.
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