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Matthias Kaeppler
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 Posted: Sun Feb 27, 2005 6:55 pm Post subject: Dereference Adaptor |
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Hello,
I need to sort a range of pointers with a predicate which applies to the
pointees. I tried to use boost::indirect_iterator, however, this will
sort the container with the pointees instead the one with the pointers:
vector<int> coll;
// ...
vector<int*> ptrcoll;
// ...
indirect_iterator< vector begin(ptrcoll.begin()),
end(ptrcoll.end());
sort( begin, end ); // this sorts coll, not ptrcoll, what have I gained?
Instead, is there some sort of adaptor, which allows things like this:
vector<int> coll;
// ...
vector<int*> ptrcoll;
// ...
sort( ptrcoll.begin(), ptrcoll.end(), dereference( less<int>() ) );
.... where dereference is an adaptor taking the function/functor
representing the predicate on the pointees.
--
Matthias Kaeppler
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Kurt Krueckeberg
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| Posted: Sun Feb 27, 2005 8:36 pm Post subject: Re: Dereference Adaptor |
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| Quote: | I need to sort a range of pointers with a predicate which applies to the
pointees. I tried to use boost::indirect_iterator, however, this will sort
the container with the pointees instead the one with the pointers:
vector<int> coll;
// ...
vector<int*> ptrcoll;
sort( ptrcoll.begin(), ptrcoll.end(), dereference( less<int>() ) );
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template<typename T> class DerefPtr {
T *t_;
public:
DerefPtr(T *x) : t_(x) {}
T operator *() const;
};
vector<Ptr ptrcoll;
sort( ptrcoll.begin(), ptrcoll.end(), less<int>() );
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Matthias Kaeppler
Guest
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| Posted: Sun Feb 27, 2005 8:51 pm Post subject: Re: Dereference Adaptor |
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Kurt Krueckeberg wrote:
| Quote: | I need to sort a range of pointers with a predicate which applies to the
pointees. I tried to use boost::indirect_iterator, however, this will sort
the container with the pointees instead the one with the pointers:
vector<int> coll;
// ...
vector<int*> ptrcoll;
sort( ptrcoll.begin(), ptrcoll.end(), dereference( less<int>() ) );
template<typename T> class DerefPtr {
T *t_;
public:
DerefPtr(T *x) : t_(x) {}
T operator *() const;
};
vector<Ptr ptrcoll;
sort( ptrcoll.begin(), ptrcoll.end(), less<int>() );
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And what is this supposed to do? ^^
operator* has no body. And I guess vector<Ptr is supposed to be
vector<DerefPtr ?
--
Matthias Kaeppler
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Kurt Krueckeberg
Guest
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| Posted: Mon Feb 28, 2005 5:42 pm Post subject: Re: Dereference Adaptor |
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| Quote: | And what is this supposed to do? ^^
operator* has no body. And I guess vector<Ptr is supposed to be
vector<DerefPtr ?
Sorry for the confusion. |
#include "stdafx.h"
#include <vector>
#include <functional>
#include <algorithm>
#include <iterator>
using namespace std;
// Comparison functor for use with associative containers
struct DereferenceLess {
public:
template<typename PtrType> bool operator()(PtrType pT1, PtrType pT2)
{
return *pT1 < *pT2;
}
};
struct Dereference {
template
{
return *ptr;
}
};
int main(int argc, char *argv[])
{
int *pi3 = new int( ;
int *pi = new int(10);
int *pi2 = new int(9);
int *pi4 = new int(7);
vector<int* > vec;
vec.push_back(pi);
vec.push_back(pi2);
vec.push_back(pi3);
vec.push_back(pi4);
sort(vec.begin(), vec.end(), DereferenceLess());
transform(vec.begin(), vec.end(), ostream_iterator<int>(cout, "n"),
Dereference() );
set<int *, DereferenceLess> s;
s.insert(pi1);
s.insert(pi2);
s.insert(pi3);
s.insert(pi4);
transform(vec.begin(), vec.end(), ostream_iterator<int>(cout, "n"),
Dereference() );
return 0;
}
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