loop on a map same way as array

Question

I'm trying to loop on containers(map, set,vector,list) and array the same way. Here is the code:

template<typename TYPE>
void AddXmlOfContAttribute(TYPE *it)
{
    m_ss<<"<SingleNode ";
    AddXmlAttribute("Value" , *it);
    m_ss<<"/>\n";
}



template<typename TYPE1,typename TYPE2>
void AddXmlOfContAttribute(std::pair<TYPE1,TYPE2> tpair)
{
    m_ss<<"<MapNode ";
    AddXmlAttribute("key"   , tpair->first);
    AddXmlAttribute("Value" , tpair->second);
    m_ss<<"/>\n";
}




template<typename TYPE>
    void AddContainerToXml(std::string str, TYPE it_begin ,  TYPE it_end)
    {
        if(it_begin != it_end)
        {
            m_ss<<"<"<<str<<">\n";

            //std::for_each(it_begin , it_end, AddXmlOfContAttribute);

            for( ; it_begin != it_end ; it_begin++)
                AddXmlOfContAttribute(it_begin);

            m_ss<<"</"<<str<<">\n";
        }
    }

I get the following error:

In member function ‘void AddElementToBackupFileFunctor::AddContainerToXml(CrString, TYPE, TYPE) [with TYPE = std::_Rb_tree_const_iterator >]’ instantiated from here error: no matching function for call to
AddElementToBackupFileFunctor::AddXmlOfContAttribute(std::_Rb_tree_const_iterator >&)’

How do i do it in normal loop? Bonus question :How do i do it in for_each loop?

score 1 · Answer 1 · edited May 23 '17 at 12:27

1

So, in short, I have constructed an example that should explain all you need here.

In order to do what you want, you have to first change your handlers to structs with static methods (this is required because you cannot partially specialize function templates, see here):

template<typename TYPE>
struct value_handler {
    static void AddXmlOfContAttribute(AddElementToBackupFileFunctor& context, 
                                      TYPE value) {
        // handle normal values here
        // context replaces this-pointer
    }
};

// partial specialization for pairs
template<typename TYPE1, typename TYPE2>
struct value_handler<std::pair<TYPE1, TYPE2> > {
    static void AddXmlOfContAttribute(AddElementToBackupFileFunctor& context, 
                                      std::pair<TYPE1, TYPE2> value) {
        // handle values that are pairs here
        // context replaces this-pointer
    }
};

The value-parameters cannot be references, because that would screw up std::bind1st (a workaround using Boost is described here). To use this with std::for_each, do the following:

std::for_each(begin, end, std::bind1st(
    std::ptr_fun(&AddElementToBackupFileFunctor::value_handler<typename TYPE::value_type>::AddXmlOfContAttribute), 
    *this));

edited May 23 '17 at 12:27

Community

1
1

answered Jun 22 '11 at 09:13

Björn Pollex

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Ok , what about the call to the map function? Can i also call it with TYPE & ? – DavidBobo Jun 22 '11 at 09:22
AddXmlOfContAttribute(std::pair tpair) – DavidBobo Jun 22 '11 at 09:26
This is what the second part of my answer shows. I will explain further in a moment. – Björn Pollex Jun 22 '11 at 09:30
@David: I have posted a new answer that does the automatic specialization you want with `std::for_each`. – Björn Pollex Jun 22 '11 at 10:25
Thank u for the answer. I think i'll use the regular loop solution. I don't see any advatage in using for_each. Tell me if i'm wrong but, ususally for_each is only a matter of esthetic. And here it made it more complicated. – DavidBobo Jun 22 '11 at 11:12

progician · Answer 2 · 2011-06-22T09:43:05.967

0

The compilation error comes from this line:

AddXmlOfContAttribute(it_begin);

This should be:

AddXmlOfContAttribute(*it_begin);

I am a moron I didn't realize the first overload... that should be the reference as sc said.

edited Jun 22 '11 at 09:43

answered Jun 22 '11 at 09:36

progician

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loop on a map same way as array

2 Answers2