Template Compare iterator

Question

I have a class that is declared as follows comparator:

    template <typename _Type, typename _Comparator = std::equal_to<typename _Type::value_type> >
        class CSearch {
public:    
    CSearch() : comp(_Comparator()) {
    };

    CSearch(const _Comparator &_cmp) : comp(_cmp) {
    };
    void Add(int id, const _Type & needle);
    set<int> Search(const _Type & hayHeap) const;    
protected:
    _Comparator comp;
    vector<pair<int, _Type> > m_Db;
};

template <typename _Type, typename _Comparator>
void CSearch<_Type, _Comparator>::Add(int id, const _Type& needle) {
    m_Db.push_back(pair<int, _Type>(id, needle));
}

template <typename _Type, typename _Comparator>
set<int> CSearch<_Type, _Comparator>::Search(const _Type & hayHeap) const {
    set<int> s_search; 
    typename vector< pair<int, _Type> >::const_iterator it;
    typename _Type::const_iterator hayStackIterator;

    for (hayStackIterator = hayHeap.begin(); hayStackIterator != hayHeap.end(); ++hayStackIterator){        
        for(it=m_Db.begin(); it!=m_Db.end(); ++it){
            if(comp(*it, *hayStackIterator))
                s_search.insert(it->first);                
        }
    }
    return s_search;
}

//-------------------
int main(int argc, char** argv) {

    CSearch <string> test1;
    test1 . Add    ( 0, "hello" );
    test1 . Add    ( 1, "world" );
    test1 . Add    ( 2, "rld" );
    test1 . Add    ( 3, "ell" );
    test1 . Add    ( 4, "hell" );
    printSet ( test1 . Search ( "hello world!" ) );
    // 0, 1, 2, 3, 4
    printSet ( test1 . Search ( "hEllo world!" ) );
    // 1, 2

    CSearch <string, bool (*)(const char &, const char &)> test2 ( upperCaseCompare );
    test2 . Add    ( 0, "hello" );
    test2 . Add    ( 1, "world" );
    test2 . Add    ( 2, "rld" );
    test2 . Add    ( 3, "ell" );
    test2 . Add    ( 4, "hell" );
    printSet ( test2 . Search ( "HeLlO WoRlD!" ) );
    // 0, 1, 2, 3, 4
    printSet ( test2 . Search ( "hallo world!" ) );
    // 1, 2

    CSearch <string, CharComparator> test3 ( CharComparator ( false ) );
    test3 . Add    ( 0, "hello" );
    test3 . Add    ( 1, "world" );
    test3 . Add    ( 2, "rld" );
    test3 . Add    ( 3, "ell" );
    test3 . Add    ( 4, "hell" );
    printSet ( test3 . Search ( "heLLo world!" ) );
    // 0, 1, 2, 3, 4
    printSet ( test3 . Search ( "Well, templates are hell" ) );
    return 0;

}

The Search function does not translate condition:

if(comp(*it, *hayStackIterator))...

Can you help?

Translate error:

main.cpp:101:44: instantiated from here main.cpp:55:13: error: no match for call to ‘(const std::equal_to) (const std::pair >&, const char&)’ /usr/include/c++/4.6/bits/stl_function.h:205:12: note: candidate is: /usr/include/c++/4.6/bits/stl_function.h:208:7: note: bool std::equal_to<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = char] /usr/include/c++/4.6/bits/stl_function.h:208:7: note: no known conversion for argument 1 from ‘const std::pair >’ to ‘const char&’ main.cpp: In member function ‘std::set CSearch<_Type, _Comparator>::Search(const _Type&) const [with _Type = std::basic_string, _Comparator = bool (*)(const char&, const char&)]’: main.cpp:112:44: instantiated from here main.cpp:55:13: error: invalid initialization of reference of type ‘const char&’ from expression of type ‘const std::pair >’ main.cpp: In member function ‘std::set CSearch<_Type, _Comparator>::Search(const _Type&) const [with _Type = std::basic_string, _Comparator = CharComparator]’: main.cpp:123:44: instantiated from here main.cpp:55:13: error: no match for call to ‘(const CharComparator) (const std::pair >&, const char&)’ main.cpp:64:7: note: candidate is: main.cpp:69:16: note: bool CharComparator::operator()(const char&, const char&) const main.cpp:69:16: note: no known conversion for argument 1 from ‘const std::pair >’ to ‘const char&’ main.cpp: In member function ‘std::set CSearch<_Type, _Comparator>::Search(const _Type&) const [with _Type = std::vector, _Comparator = std::equal_to]’: main.cpp:134:52: instantiated from here main.cpp:55:13: error: no match for call to ‘(const std::equal_to) (const std::pair >&, const int&)’ /usr/include/c++/4.6/bits/stl_function.h:205:12: note: candidate is: /usr/include/c++/4.6/bits/stl_function.h:208:7: note: bool std::equal_to<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = int] /usr/include/c++/4.6/bits/stl_function.h:208:7: note: no known conversion for argument 1 from ‘const std::pair >’ to ‘const int&’ main.cpp: In member function ‘std::set CSearch<_Type, _Comparator>::Search(const _Type&) const [with _Type = std::vector >, _Comparator = std::equal_to >]’: main.cpp:145:53:
instantiated from here main.cpp:55:13: error: no match for call to ‘(const std::equal_to >) (const std::pair > >&, const std::basic_string&)’ /usr/include/c++/4.6/bits/stl_function.h:205:12: note: candidate is: /usr/include/c++/4.6/bits/stl_function.h:208:7: note: bool std::equal_to<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = std::basic_string] /usr/include/c++/4.6/bits/stl_function.h:208:7: note: no known conversion for argument 1 from ‘const std::pair > >’ to ‘const std::basic_string&’

Can't you cut your code down to the parts that are relevant to the problem? — 0x499602D2
Your code is not compilable. printSet, upperCaseCompare, CharComparator were not found. — gongzhitaao

awesoon awesoon · Accepted Answer · 2013-05-05T15:37:36

The error message is pretty clear.

if(comp(*it, *hayStackIterator))

*it has type const std::pair<int, std::string>&, but *hayStackIterator has type const char&. You can't compare them.

Template Compare iterator

1 Answers