compilation error with merge algorithm

[subramanian100in]

Consider the following program:

#include <cstdlib>
#include <iostream>
#include <set>
#include <map>
#include <algorithm>
#include <iterator>
#include <utility>

using namespace std;

int main()
{
typedef pair<int, intp_type;

multiset<p_type c1;

c1.insert(make_ pair(0, 2));
c1.insert(make_ pair(0, 0));
c1.insert(make_ pair(0, 1));
c1.insert(make_ pair(2, 3));

multimap<int, intc3;

c3.insert(make_ pair(5, 0));
c3.insert(make_ pair(0, 0));
c3.insert(make_ pair(3, 2));
c3.insert(make_ pair(0, -1));
c3.insert(make_ pair(1, -1));

multimap<int, intdest;

merge(c1.begin( ), c1.end(), c3.begin(), c3.end(),
inserter(dest, dest.begin()));

return EXIT_SUCCESS;
}

Suppose the above program is named z.cpp and is compiled as
g++ -std=c++98 -pedantic -Wall -Wextra z.cpp

Then I get compilation error for the line
merge(...)

z.cpp:32: instantiated from here
/usr/lib/gcc/i386-redhat-linux/3.4.3/../../../../include/c++/3.4.3/
bits/stl_algo.h:2979 : error: no match for 'operator<' in '(&__first2)-

>std::_Rb_tree_ iterator<_Tp>:: operator* [with _Tp = std::pair<const

int, int>]() < (&__first1)-

>std::_Rb_tree_ const_iterator< _Tp>::operator* [with _Tp =

main()::p_type]()'

Kindly help me to fix this compilation error.

Thanks
V.Subramanian

[Barry]

su************* *@yahoo.com, India wrote:

Consider the following program:

#include <cstdlib>
#include <iostream>
#include <set>
#include <map>
#include <algorithm>
#include <iterator>
#include <utility>

using namespace std;

int main()
{
typedef pair<int, intp_type;

multiset<p_type c1;

c1.insert(make_ pair(0, 2));
c1.insert(make_ pair(0, 0));
c1.insert(make_ pair(0, 1));
c1.insert(make_ pair(2, 3));

multimap<int, intc3;

c3.insert(make_ pair(5, 0));
c3.insert(make_ pair(0, 0));
c3.insert(make_ pair(3, 2));
c3.insert(make_ pair(0, -1));
c3.insert(make_ pair(1, -1));

multimap<int, intdest;

merge(c1.begin( ), c1.end(), c3.begin(), c3.end(),
inserter(dest, dest.begin()));

return EXIT_SUCCESS;
}

Suppose the above program is named z.cpp and is compiled as
g++ -std=c++98 -pedantic -Wall -Wextra z.cpp

Then I get compilation error for the line
merge(...)

z.cpp:32: instantiated from here
/usr/lib/gcc/i386-redhat-linux/3.4.3/../../../../include/c++/3.4.3/
bits/stl_algo.h:2979 : error: no match for 'operator<' in '(&__first2)-

>std::_Rb_tree_ iterator<_Tp>:: operator* [with _Tp = std::pair<const

int, int>]() < (&__first1)-

>std::_Rb_tree_ const_iterator< _Tp>::operator* [with _Tp =

main()::p_type]()'

Kindly help me to fix this compilation error.

typeof "multiset<p_typ e>::value_type " == p_type == pair<int, int... Type1
typeof "multimap<i nt, int>::value_typ e" == pair<const int, int ... Type2

Type1. Type2 are two different specialization of template class pair

so there are no specialization of
template <class T1, class T2>
bool operator<(const pair<T1, T2>& x, const pair<T1, T2>& y);

while the 5-arg merge needs operator<
take a look at the implementation of merge.

--
Best Regards
Barry

[Barry]

Barry wrote:

su************* *@yahoo.com, India wrote:

>Consider the following program:

#include <cstdlib>
#include <iostream>
#include <set>
#include <map>
#include <algorithm>
#include <iterator>
#include <utility>

using namespace std;

int main()
{
typedef pair<int, intp_type;

multiset<p_type c1;

c1.insert(make_ pair(0, 2));
c1.insert(make_ pair(0, 0));
c1.insert(make_ pair(0, 1));
c1.insert(make_ pair(2, 3));

multimap<int, intc3;

c3.insert(make_ pair(5, 0));
c3.insert(make_ pair(0, 0));
c3.insert(make_ pair(3, 2));
c3.insert(make_ pair(0, -1));
c3.insert(make_ pair(1, -1));

multimap<int, intdest;

merge(c1.begin( ), c1.end(), c3.begin(), c3.end(),
inserter(des t, dest.begin()));

return EXIT_SUCCESS;
}

Suppose the above program is named z.cpp and is compiled as
g++ -std=c++98 -pedantic -Wall -Wextra z.cpp

Then I get compilation error for the line
merge(...)

z.cpp:32: instantiated from here
/usr/lib/gcc/i386-redhat-linux/3.4.3/../../../../include/c++/3.4.3/
bits/stl_algo.h:2979 : error: no match for 'operator<' in '(&__first2)-

>>std::_Rb_tree _iterator<_Tp>: :operator* [with _Tp = std::pair<const

int, int>]() < (&__first1)-

>>std::_Rb_tree _const_iterator <_Tp>::operator * [with _Tp =

main()::p_ty pe]()'

Kindly help me to fix this compilation error.

typeof "multiset<p_typ e>::value_type " == p_type == pair<int, int... Type1
typeof "multimap<i nt, int>::value_typ e" == pair<const int, int ... Type2

Type1. Type2 are two different specialization of template class pair

so there are no specialization of
template <class T1, class T2>
bool operator<(const pair<T1, T2>& x, const pair<T1, T2>& y);

while the 5-arg merge needs operator<
take a look at the implementation of merge.

"merge" also requires the two value_type to be the same type.

--
Best Regards
Barry

[Christian Hackl]

su************* *@yahoo.com, India wrote:

int main()
{
typedef pair<int, intp_type;

multiset<p_type c1;

c1.insert(make_ pair(0, 2));
c1.insert(make_ pair(0, 0));
c1.insert(make_ pair(0, 1));
c1.insert(make_ pair(2, 3));

multimap<int, intc3;

c3.insert(make_ pair(5, 0));
c3.insert(make_ pair(0, 0));
c3.insert(make_ pair(3, 2));
c3.insert(make_ pair(0, -1));
c3.insert(make_ pair(1, -1));

multimap<int, intdest;

merge(c1.begin( ), c1.end(), c3.begin(), c3.end(),
inserter(dest, dest.begin()));

return EXIT_SUCCESS;
}

[...]

z.cpp:32: instantiated from here
/usr/lib/gcc/i386-redhat-linux/3.4.3/../../../../include/c++/3.4.3/
bits/stl_algo.h:2979 : error: no match for 'operator<' in '(&__first2)-

>std::_Rb_tree_ iterator<_Tp>:: operator* [with _Tp = std::pair<const

int, int>]() < (&__first1)-

>std::_Rb_tree_ const_iterator< _Tp>::operator* [with _Tp =

main()::p_type]()'

The value type of your multimap is actually std::pair<const int, int>.
However, std::pair<const int, intand std::pair<int, intare unrelated
types. The basic problem of type incompatibility can be illustrated by a
simpler example:

#include <utility>

int main()
{
std::pair<const int, inta;
std::pair<int, intb;

a < b; // error
}

Depending on how big your containers really are and how often that piece
of code is executed, a viable solution may be copying your
std::pair<const int, intelements from the multimap into a new range of
std::pair<int, intand use that one in std::merge.
--
Christian Hackl