Change class variable after finding - c++

Question

I am currently working on a chess engine in C++, and in the engine, I'm trying to modify a string variable "piece" inside of a class "ChessTile" within another class called "ChessBoard".
Anyways when I use a function to return a class, then modify said class, it doesn't change the source variable, and I was wondering how you do that.
Here is a simple script I wrote to demonstrate:
#include <iostream>
#include <string>
class child {
private:
int myVar;
public:
child(int v) {
myVar = v;
}
int getVar() {
return myVar;
}
int setVar(int Svar) {
this->myVar = Svar;
return 0;
}
};
class parent {
public:
child baby = child(0);
child findMyChild(int var) {
if (var == 1) {
return baby;
}
}
};
parent DAD;
int main() {
std::cout << DAD.findMyChild(1).getVar() << std::endl;
DAD.findMyChild(1).setVar(50);
std::cout << DAD.findMyChild(1).getVar() << std::endl;
}
The output for this is:
0
0
But I'm wanting it to be:
0
50
If necessary, I can also post my chess engine. Thank you!

Answer 1

In your code, findMyChild() is returning a copy of the baby ( function returning by value), use return by reference instead like so.
child& parent::findMyChild(int var) {
if (var == 1)
{
return baby;
}
/* other codes */
return baby;
}

Answer 2

You are returning a copy of child in findMyChild. Therefore, you modify only that copy, not the member itself.
You should return a pointer to the member
child* findMyChild(int var) {
return var == 1
? &baby
: nullptr;
}
then dereference it to get/set its value. For example:
DAD.findMyChild(1)->setVar(50);
Since findMyChild can return null pointer in my code you should check its existence before accessing
child* c = DAD.findMyChild(1);
if (c) c->setVar(50);

Answer 3

You can do it via returning pointer/reference of child as stated by another comment or you can do it via an interface in parent class.
#include <iostream>
#include <string>
#define FIRST_CHILD 1
#define CANNOT_FIND_CHILD -1
class child {
private:
int myVar;
public:
child(int v) {
myVar = v;
}
int childGetVar() {
return myVar;
}
int childSetVar(int Svar) {
this->myVar = Svar;
return 0;
}
};
class parent {
public:
child baby = child(0);
int getVar(int var) {
if (var == FIRST_CHILD)
return baby.childGetVar();
return CANNOT_FIND_CHILD;
}
int setVar(int var, int Svar) {
if (var == FIRST_CHILD)
baby.childSetVar(Svar);
return CANNOT_FIND_CHILD;
}
};
parent DAD;
int main() {
std::cout << DAD.getVar(FIRST_CHILD) << std::endl;
DAD.setVar(FIRST_CHILD, 50);
std::cout << DAD.getVar(FIRST_CHILD) << std::endl;
}