Trying to write a std::iterator : Compilation error
- by Naveen
I am trying to write an std::iterator for the CArray<Type,ArgType> MFC class. This is what I have done till now:
template <class Type, class ArgType>
class CArrayIterator : public std::iterator<std::random_access_iterator_tag, ArgType>
{
public:
CArrayIterator(CArray<Type,ArgType>& array_in, int index_in = 0)
: m_pArray(&array_in), m_index(index_in)
{
}
void operator++() { ++m_index; }
void operator++(int) { ++m_index; }
void operator--() { --m_index; }
void operator--(int) { --m_index; }
void operator+=(int n) { m_index += n; }
void operator-=(int n) { m_index -= n; }
typename ArgType operator*() const{ return m_pArray->GetAt(m_index); }
typename ArgType operator->() const { return m_pArray->GetAt(m_index); }
bool operator==(const CArrayIterator& other) const
{
return m_pArray == other.m_pArray && m_index == other.m_index;
}
bool operator!=(const CArrayIterator& other) const
{
return ! (operator==(other));
}
private:
CArray<Type,ArgType>* m_pArray;
int m_index;
};
I also provided two helper functions to create the iterators like this:
template<class Type, class ArgType>
CArrayIterator<Type,ArgType> make_begin(CArray<Type,ArgType>& array_in)
{
return CArrayIterator<Type,ArgType>(array_in, 0);
}
template<class Type, class ArgType>
CArrayIterator<Type,ArgType> make_end(CArray<Type,ArgType>& array_in)
{
return CArrayIterator<Type,ArgType>(array_in, array_in.GetSize());
}
To test the code, I wrote a simple class A and tried to use it like this:
class A
{
public:
A(int n): m_i(n)
{
}
int get() const
{
return m_i;
}
private:
int m_i;
};
struct Test
{
void operator()(A* p)
{
std::cout<<p->get()<<"\n";
}
};
int main(int argc, char **argv)
{
CArray<A*, A*> b;
b.Add(new A(10));
b.Add(new A(20));
std::for_each(make_begin(b), make_end(b), Test());
return 0;
}
But when I compile this code, I get the following error:
Error 4 error C2784: 'bool
std::operator <(const
std::_Tree<_Traits &,const
std::_Tree<_Traits &)' : could not
deduce template argument for 'const
std::_Tree<_Traits &' from
'CArrayIterator' C:\Program
Files\Microsoft Visual Studio
9.0\VC\include\xutility 1564 Vs8Console
Can anybody throw some light on what I am doing wrong and how it can be corrected? I am using VC9 compiler if it matters.
