C / C ++中的任意大小整数 [英] Arbitrary size integers in C/C++

问题描述

• 有没有办法用c / c ++创建任意大小的整数？

例如：

int main(void) {
  Int i = Int(3); //3-bit integer
  i = 1; //Represented as: 001
}

---

奖金

• 有没有办法对浮动值做同样的事情？



推荐答案

你不能创建大小小于 char 的整数（也就是说，每个对象都有以字节为单位的大小，是 sizeof（char）的倍数，即1）。但这不是问题，因为你可以在更大的数字内打包数字。

You can't create integers of size less than char (that is, each object has a size in bytes that's a multiple of sizeof(char), which is 1). But that's not a problem since you can pack numbers inside a larger number.

const unsigned size_in_bits = 3;
unsigned a = 1; // 001
unsigned b = 5; // 101
unsigned packed = (b << size_in_bits*1) | (a << size_in_bits*0); // 101001
unsigned unpacked_a = (packed >> size_in_bits*0) & ((1 << size_in_bits)-1);
unsigned unpacked_b = (packed >> size_in_bits*1) & ((1 << size_in_bits)-1);

或使用位域（语法更好，但二进制布局是实现定义的）

or use bitfields (the syntax is nicer, but the binary layout is implementation-defined)

struct Date
{
    unsigned day : 5;
    unsigned month : 4;
    unsigned year : 21; 
};

Date d;
d.day = 5; d.month = 11; d.year = 2014;

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