在C ++中，将数据存储在矢量对象中的效率如何？

Question

I'm making a small virtual machine; in my virtual machine I read instructions from a binary file. Each instruction is 1 byte in size. When the VM starts, it loads the binary file into a vector. Then I use a switch and a for loop to execute the instructions.

But here's where my question starts. I have a vector called "Stack"; it's my virtual machines stack for the program that's running. The problem is I want to store different kinds of data in the vector (Signed and Unsigned Integers, Strings, etc ...).

To do this I created my own object (robj) and made the vector of type "robj". This lets me store the kind of data I want, but my question is: is this wasteful?

Here's the implementation of my object:

class robj {

public:
    int signed_int = 0;
    unsigned int unsigned_int = 0;

};

As you can see, my object is really small at the moment, but it will get larger as I add things like strings. The part that I think is wasteful is that, if I store a signed integer on the stack I also have to store an unsigned one because the object defines both types of integers. And this problem will only get worse as I make the object bigger.

So I'd just like to know, is there a less wasteful way to do this?

Answer 1

This is what Boost.Variant is for. It implements discriminated unions so you don't have to:

std::vector<boost::variant<
   int,
   unsigned int
>> v;

Answer 2

There can be 2 solutions

1. Use union

union robj {
  int signed_int;
  unsigned int unsigned int;
};

2. Use inheritance

class type_base
{
  type_data my_type;
public:
  type_base(const type_data &t) : my_type(t) {}
  virtual parse_data() = 0;
  virtual serialize_data() = 0;
  virtual type_data get_type() {
    return my_type;
  }
  virtual type_base *clone() = 0;
};

class signed_int : public type_base {
public:
  int signed_int;
};

You can also templatize your type where the template inherits from type_base.

^{Make sure that you never make a vector of type_base which can cause object slicing. Thanks to Alain for his comment}