C++ Object Creation through Inputs - c++

Question

I would like to create objects of a class with the name of an input
class Rectangle {
public:
int width;
int height;
...
//assume a constructor that assigns (width, height)
}
how would i generate an object of a new name using an input. (not me typing Rectangle myRectangle(1,1); )
assume that there is anywhere from 1 to infinite objects created by the user
(i am not looking for help with the human input, or checking if they still want an input, solely how to use an input to create a uniquely named object)
this is my first stack overflow post so please inform me if i did something wrong.
Cheers,
Coal lad

Answer 1

You can use a map from (user supplied) class name to a factory function.
class Creatable {
virtual ~Creatable() {}
};
class Rectangle : public Creatable {
int width;
int height;
};
class Circle : public Creatable {
int radius;
};
// assume suitable constructors for these
// Given a string (with parameters such as the
// radius or width/height) construct an object
// and return a managed pointer to it
using FactoryFunction_t =
std::function<std::unique_ptr<Creatable>(std::string const &)>;
// maps for example "rectangle" to a function which parses width and height from the string and returns an allocated rectangle
std::map<std::string, FactoryFunction_t> factories;
factories.insert({{"rectangle", CreateRectangle}, {"circle", CreateCircle}});
factories.at("rectangle")("width=21; height=42;");
Instead of using polymorphism (a common base class) you can also use std::variant if the possible classes are known at compile time.
Instead of having each factory function parse a string you can also parse the parameters before - for example into a map parameter name -> parameter value and pass that to the factory functions.
If you want to let the user name the created objects then you could keep the managed pointers from above in a map:
std::map<std::string, std::unique_ptr<Creatable>> objects;
objects["my_rectangle"] = factories.at("rectangle")("width=21; height=42;");
This could be the result from input from the user similar to this:
my_rectangle = rectangle(width=21;height=42;);

Answer 2

#include<vector>
class Rectangle {
public:
int width;
int height;
};
int main(){
/*You can't use unique names. You can use a vector of objects
std::vector<Rectangles> rectsVector; and then when you want
to create anew object ask the user for (width,height) then
rectVector.push_back(Rectangle{width,height}) and so on*/
std::vector<Rectangle> rectsVector;
size_t width{3},height{2};
rectsVector.push_back(Rectangle{width,height});
return 0;
}