«

I need to implement a function with a argument that is a compare
function.
This compare function must be several for every necessity.
For example , I would like a compare function to analyze element of
list that are even or a compare function to analyze odd element.


example:

void f (compare )
{

list<int> l;
list<int>::iterator it;

for (it=l.begin();l!=l.end();++it)
{
if ( compare(it) )
{
....
}

}

}


I would like specify in my call, what type of compare function the
function f must use.
Exist a template solution for that?

On 7 Mar, 12:26, "antani" <antani8...@yahoo.it> wrote:
> I need to implement a function with a argument that is a compare
> function.
> This compare function must be several for every necessity.
> For example , I would like a compare function to analyze element of
> list that are even or a compare function to analyze odd element.
>
> example:
>
> void f (compare )
> {
>
> list<int> l;
> list<int>::iterator it;
>
> for (it=l.begin();l!=l.end();++it)
> {
> if ( compare(it) )
> {
> ....
> }
>
> }
>
> }
>
> I would like specify in my call, what type of compare function the
> function f must use.
> Exist a template solution for that?

I'm not quite sure I understand what you want but you probably want to
use templates here, something like:

template<typename CMP>
void f(CMP comp)
{
list<int> l;
list<int>::iterator it;

for (it=l.begin();l!=l.end();++it)
{
if ( comp(it) )
{
....
}
}
}

This way you can use either a functor or a normal function when
calling f().

--
Erik Wikström

On Mar 7, 1:26 pm, "antani" <antani8...@yahoo.it> wrote:
> I need to implement a function with a argument that is a
> compare function.
> This compare function must be several for every
> necessity. For example , I would like a compare function
> to analyze element of list that are even or a compare
> function to analyze odd element.

I almost choked on my coffee when my compiler didn't choke
on the following:

#include <iostream>
#include <ostream>
#include <list>

template < typename T >
bool fredle ( T x ) { return ( * x ) % 2 ; }

template < typename T >
bool bargle ( T x ) { return ! ( ( * x ) % 2 ) ; }

template < typename T >
bool quugle ( T x ) { return ! ( ( * x ) % 3 ) ; }

template < typename T >
bool xyzzle ( T x ) { return quugle ( -- x ) ; }

template < typename T >
void f
(
const T & l ,
bool ( * c ) ( typename T :: const_iterator )
)
{
for
(
typename T :: const_iterator i = l . begin ( ) ;
i != l . end ( ) ; ++ i
)
if ( ( * c ) ( i ) ) std :: cout << ( * i ) << " " ;
std :: cout << std :: endl ;
}

int main ( )
{
std :: list < int > l ;
for ( int i = 0 ; i != 10 ; ++ i )
l . push_back ( i + 1 ) ;
f ( l , & fredle ) ;
f ( l , & bargle ) ;
f ( l , & quugle ) ;
f ( l , & xyzzle ) ;
}

Looks like a disaster waiting to happen to me.

--
Pavel Lepin

> template<typename CMP>
> void f(CMP comp)
> {
> list<int> l;
> list<int>::iterator it;
>
> for (it=l.begin();l!=l.end();++it)
> {
> if ( comp(it) )
> {
> ....
> }
> }
> }
>
> This way you can use either a functor or a normal function when
> calling f().

Can you write a example how declare a CMP comp?

On 3ÔÂ7ÈÕ, ÏÂÎç9ʱ46·Ö, "antani" <antani8...@yahoo.it> wrote:
> > template<typename CMP>
> > void f(CMP comp)
> > {
> > list<int> l;
> > list<int>::iterator it;
>
> > for (it=l.begin();l!=l.end();++it)
> > {
> > if ( comp(it) )
> > {
> > ....
> > }
> > }
> > }
>
> > This way you can use either a functor or a normal function when
> > calling f().
>
> Can you write a example how declare a CMP comp?- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
>
for example:

#include <iostream>

// the normal function
void foo()
{
std::cout << "foo" << std::endl;
}

// the function object
class bar
{
void operator ()(){
std::cout << "bar" << std::endl;
}
}

template <typename CMP>
void foobar(CMP cmp)
{
cmp();
}

int main()
{
foobar(foo);
foobar(bar());

return 0;
}
> - ÏÔʾÒýÓõÄÎÄ×Ö -

On 3ÔÂ7ÈÕ, ÏÂÎç10ʱ19·Ö, "Wayne Shu" <Wayne...@gmail.com> wrote:
> On 3ÔÂ7ÈÕ, ÏÂÎç9ʱ46·Ö, "antani" <antani8...@yahoo.it> wrote:
>
>
>
> > > template<typename CMP>
> > > void f(CMP comp)
> > > {
> > > list<int> l;
> > > list<int>::iterator it;
>
> > > for (it=l.begin();l!=l.end();++it)
> > > {
> > > if ( comp(it) )
> > > {
> > > ....
> > > }
> > > }
> > > }
>
> > > This way you can use either a functor or a normal function when
> > > calling f().
>
> > Can you write a example how declare a CMP comp?- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
>
> for example:
>
> #include <iostream>
>
> // the normal function
> void foo()
> {
> std::cout << "foo" << std::endl;
>
> }
>
> // the function object
> class bar
> {
sorry I have forgotten to add the access level.
public:
> void operator ()(){
> std::cout << "bar" << std::endl;
> }
>
> }
>
> template <typename CMP>
> void foobar(CMP cmp)
> {
> cmp();
>
> }
>
> int main()
> {
> foobar(foo);
> foobar(bar());
>
> return 0;
>
>
>
> }
> > - ÏÔʾÒýÓõÄÎÄ×Ö -- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
>
> - ÏÔʾÒýÓõÄÎÄ×Ö -- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
>
> - ÏÔʾÒýÓõÄÎÄ×Ö -