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I want to have a data variable which will be an integer and its range will be from 0 - 1.000.000. For example normal int variables can store numbers from -2,147,483,648 to 2,147,483,647. I want the new data type to have less range so it can have LESS SIZE.

If there is a way to do that please let me know?

Brian Tompsett - 汤莱恩
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user3302398
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  • do you only need to store them or will you do some arithmetic ? – Michael M. Feb 12 '14 at 16:03
  • An integer type that has less range is far, far easier than one that has less range *and* has less size. You understand that your 0 to 1 million value would require 63% of the size of the standard integer, and would be much much slower? – Yakk - Adam Nevraumont Feb 12 '14 at 16:15

3 Answers3

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There isn't; you can't specify arbitrary ranges for variables like this in C++.

You need 20 bits to store 1,000,000 different values, so using a 32-bit integer is the best you can do without creating a custom data type (even then you'd only be saving 1 byte at 24 bits, since you can't allocate less than 8 bits).

As for enforcing the range of values, you could do that with a custom class, but I assume your goal isn't the validation but the size reduction.

TypeIA
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So, there's no true good answer to this problem. Here are a few thoughts though:

  1. If you're talking about an array of these 20 bit values, then perhaps the answers at this question will be helpful: Bit packing of array of integers

  2. On the other hand, perhaps we are talking about an object, that has 3 int20_ts in it, and you'd like it to take up less space than it would normally. In that case, we could use a bitfield.

    struct object {
    int a : 20;
    int b : 20;
    int c : 20;
} __attribute__((__packed__));

printf("sizeof object: %d\n", sizeof(struct object));

    This code will probably print 8, signifying that it is using 8 bytes of space, not the 12 that you would normally expect.

Community
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Bill Lynch
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You can only have data types to be multiple of 8 bits. This is because, otherwise that data type won't be addressable. Imagine a pointer to a 5 bit data. That won't exist.

HelloWorld123456789
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