i have a stl list of myclass and a pointer to a myclass-objects. now i do listofmyclass.push_back() to create one object of myclass. how can i now assign the pointer to the myclass-object to the new object that was just created?

listofmyclass.push_back() is invalid C++ code. You need to push back some object. If you do that you have a pointer to it.

You can do this:

listofmyclass.push_back( MyClass() );
MyClass* = &(*listofmyclass.rbegin());

I believe.

But if you do this:

list<MyClass> listofmyclass;
MyClass* mc = new MyClass();
listofmyclass.push_back(*mc);
mc = &listofmyclass.back();

you'll leak memory. The memory allocated in line 2 is copied to a new list entry in line 3. Then the pointer is set to the copy in line 4, leaving the original data allocated, but unreferenced.
Correctly, you would either:

list<MyClass> listofmyclass;
MyClass* mc = new MyClass();
listofmyclass.push_back(*mc);
delete mc;
mc = &listofmyclass.back();

or:

list<MyClass*> listofmyclass;
MyClass* mc = new MyClass();
listofmyclass.push_back(mc);
// ...and somewhere else to clean up:
MyClass* mc = &listofmyclass.pop_back();
delete mc;
// or something similar.

...in which case you will have to delete all list entries yourself when you no longer need them. The list now only holds pointers to objects.

Do the easy thing of first storing the created value in a local pointer, then push back the local pointer's value:

MyClass *obj = new MyClass();
objList.push_back(obj);

The function is front(), not first().

where?

someone said that list.push_back() is invalid.
so i have to call at last list.push_back(myclass()); ??