C / C++ / MFC

George_George wrote:

My question is, how to check whether we insert a new key/value pair or overwrite the same key with new value if we use [] operator.

George_George wrote:

using [] could never tell us whether we insert new pair or overwriting an old pair

mapped_type& operator[](const key_type& _Keyval)
     {	
           // find element matching _Keyval or insert with default mapped
	   iterator _Where = this->lower_bound(_Keyval);
           if ( _Where == this->end() || 
                this->comp(_Keyval, this->_Key(_Where._Mynode())))
			_Where = this->insert(_Where,
				value_type(_Keyval, mapped_type()));
		return ((*_Where).second);
     }

George_George wrote:

I am so bad to express my idea and question.

George_George wrote:

Sorry my English is not very good. You mean there is no way to check whether insert a new element or overwriting existing element if we use [] operator?

George_George wrote:

When using mapvariable[somekey] = somevalue to insert into a map variable, how to check whether there is conflicting key value in the map in an elegant way?

// An empty map.
map<cstring,cstring> TempMap;

// If you lookup a for a key which is not present,
// it will create empty entry and return. It won't
// throw any error.
CString LookupKey = _T("key"); // Key which is not present.
CString Value = TempMap[LookupKey];

George_George wrote:

using find is the optimum solution to check existence, and using [] could never tell us whether we insert new pair or overwriting an old pair, all are correct understanding?

ani_ikram wrote:

SetDlgItemText(IDC_EDIT1,' abc \n xyz ');

ani_ikram wrote:

yes it is working but like thie

cout << *it << endl;

  for ( it=available_music_list.begin() ; it != available_music_list.end(); it++ )
    (*it).PrintMe();

void Music::PrintMe()
{
  cout << artist << endl;
  cout << band << endl;
  cout << release_year << endl;
  // ...
}

FrankMookie wrote:

My question is how do I call show_available_music from Main.cpp.

FrankMookie wrote:

I have a similar function that shows all the bands in a list.