C++ Type casting base object to derived object

c++

Solution

`dynamic_cast` returns the casted pointer, it does not modify the parameter itself.

You need to do something like below.

// removed the & since the elements are now pointers
GradStudent* gStudent =  dynamic_cast<GradStudent*>(classRoom[1]); 
cout << gStudent->getInfo();

Caveat - for pointers, if it fails to cast `dynamic_cast` will return `nullptr`, you need to check for this to prevent a crash.

EDIT: Major Object slicing bug in your code - #1 is almost right

int arraySize = 3;
Student *classRoom;
classRoom = new Student[arraySize];

GradStudent gst1("Ta", "Da", 4444, 'A', "Death");
...
classRoom[0] = gst1;

Should be

int arraySize = 3;
Student **classRoom;
//      ^
classRoom = new Student*[arraySize];
//                     ^
GradStudent gst1("Ta", "Da", 4444, 'A', "Death");

classRoom[0] = &gst1;
//             ^

Or just

Student* classRoom[3];

GradStudent gst1("Ta", "Da", 4444, 'A', "Death");
...
classRoom[0] = gst1;

Without this, all data belonging to the derived class is lost, and the base class data alone is stored, this is called Object Slicing.

Problem

So I have a dynamically allocated array of base class. I've stored a few objects of its derived class inside the array. The student (base) class and its derived classes all have a `getInfo()` function, obviously the derived classes have overrided that base `getInfo()`. The goal is to used the `getinfo` function from the base class, then type class the two objects of the derived class, back into the derived class and use the overrided `getinfo()`. Everything up to "break" works perfect. It's figuring out how to type cast the objects back into the derived classes that's killing me. I've identified a few possible issues: 1) I didnt dynamically allocate correctly. Very possible because I hate pointers and very much suck at them. 2) I have no idea what Im doing with regard to actually type casting. A few things of note: 1) The base class getinfo is not virtual 2) I am not allowed to modify the base class. So, saviors of confusing code. What say you? Can you help this poor student out? EDIT!!! Updated code, now getting "Static_cast from Student ** to Gradstudent * is not allowed" ``` #include <iostream> #include "GradStudent.h" #include "UndergradStudent.h" int main() { int arraySize = 3; Student* classRoom[arraySize]; GradStudent gst1("Ta", "Da", 4444, 'A', "Death"); cout << gst1; UndergradStudent ust1("Bluh", "Bluh", 2222, 1); cout << ust1; Student bst1( "Blah", "Blah", 1111 ); classRoom[0] = &bst1; classRoom[1] = &gst1; classRoom[2] = &ust1; for (int x = 0; x < arraySize; x++) { cout << classRoom[x]->getInfo(); cout << endl; } cout << "TEST" << endl; GradStudent* gStudent = static_cast<GradStudent*>(&classRoom[2]); cout << gStudent->getInfo(); return 0; } ```

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