C++ what type should I use if I know the exact type from a few possible?

Question

hope you'll help me to understand. I have a class, that defines a buffer:

typedef std::variant<signed char, unsigned char, short, unsigned short, int, unsigned int, float> BufferData;

struct BufferAttribute {
  unsigned int index;
  int size = 4;
  char format = ATTRIBUTE_FORMAT::FLOAT;
  bool normalized = false;
  int stride = 0;
  int offset = 0;
  std::vector<BufferData> data;
  std::string name;
};

As you can see, I have a char that defines a format, so in the future, I will know the exact data format. But as for the data, I'm using a variant which makes me worry about the performance of the visitor. What type can I use to make it faster or better? Or do you think that Variant is a good choice?

P.S. I worrying about processing thousands of numbers from this buffer in real-time in my game app.

If you have the format already attached to it, why not just use a union? — IWonderWhatThisAPIDoes, Feb 19 '21 at 07:44
@СергейШарпов The main advantage of `std::variant` is type safety. I guess it's even a bit slower then a tuple. — Lukas-T, Feb 19 '21 at 07:56
@СергейШарпов Unlike variant, union is not foolproofed, that makes it as fast as it gets. — IWonderWhatThisAPIDoes, Feb 19 '21 at 07:58
I'm assuming that all the data in one buffer is the same... so using a `std::variant, std::vector, ...>` would make more sense to me. — super, Feb 19 '21 at 07:59
@super it's true, I like your way, it would be easier to get a correct buffer once than cast each buffer member all the time. Thank you. — Sergey Sharpov, Feb 19 '21 at 08:04
I agree with @super : you probably need a variant of vectors rather than a vector of variant. Maybe you need a variant of pairs; format>. — Bktero, Feb 19 '21 at 08:56

score 2 · Answer 1 · answered Feb 19 '21 at 07:53

If you are concerned about performance, you have to measure it in your use case. General statements wrt. performance tend to be wrong or may out date with the next compiler version and or hardware generation.

Here the general performance of std::variant has been analyzed.

If this is applicable to you is in question. You have to make sure that the ´std::variant´ in BufferAttribute actually is your hotspot. You can find the hotspots using a tool such as perf or vTune.

Thank you, I'll get in touch with these tools. – Sergey Sharpov Feb 19 '21 at 07:56 — Sergey Sharpov, Feb 19 '21 at 07:56

C++ what type should I use if I know the exact type from a few possible?

1 Answers1