为什么“是"? Access数据库中值为-1的值? [英] Why is "Yes" a value of -1 in MS Access database?

问题描述

我正在查看MS Access中的链接数据.

I'm looking at linked data in MS Access.

是/否"字段的值为-1(是)和0(否).有人可以解释为什么将这种违反直觉的值用于是"吗? (显然，它应该是1和0)

The "Yes/No" fields contain the value -1 for YES and 0 for NO. Can someone explain why such a counter-intuitive value is used for "Yes"? (Obviously, it should be 1 and 0)

我想一定有一个很好的理由，我想知道.

I imagine there must be a good reason, and I would like to know it.

推荐答案

False的二进制表示形式是0000000000000000(使用多少位取决于实现方式).如果对它执行二进制NOT运算，它将被更改为1111111111111111，即True，但这是有符号整数-1的二进制表示形式.

The binary representation of False is 0000000000000000 (how many bits are used depends on the implementation). If you perform a binary NOT operation on it, it will be changed to 1111111111111111, i.e. True, but this is the binary representation of the signed integer -1.

最高有效位置的1位表示带负号的负数.通过反转所有位并加1来更改数字的符号.这称为 Two的补码.

A bit of 1 at the most significant position signals a negative number for signed numbers. Changing the sign of a number happens by inverting all the bits and adding 1. This is called the Two's complement.

让我们更改1111111111111111的符号.首先反转；我们得到: 0000000000000000

Let us change the sign of 1111111111111111. First invert; we get: 0000000000000000

然后添加一个: 0000000000000001，这是1.

Then add one: 0000000000000001, this is 1.

这证明1111111111111111是-1的二进制表示形式.

This is the proof that 1111111111111111 was the binary representation of -1.

更新

此外，比较这些值时请勿进行比较

Also, when comparing these values do not compare

x = -1

或

x = 1

相反，请进行比较

x <> 0

这总是给出正确的结果，而与使用的约定无关.大多数实现将任何不等于零的值都视为True.

this always gives the correct result, independently of the convention used. Most implementations treat any value unequal zero as True.

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