波浪号çVS无符号整数签署 [英] Tilde C unsigned vs signed integer

问题描述

例如：

unsigned int i = ~0;

结果：最大数，我可以分配到 I

Result: Max number I can assign to i

和

signed int y = ~0;

结果： 1

为什么我得到 1 ？我不应该得到我可以分配给 y中的最大数量？

Why do I get -1? Shouldn't I get the maximum number that I can assign to y?

推荐答案

两个 4294967295 （又名 UINT_MAX ）和 1 具有相同的二进制重新$ p $ 0xFFFFFFFF的的psentation位或32位全部设置为 1 。这是因为有符号数是使用补重新presented。负数有MSB（最显著位）设置为 1 和翻转位的其余部分，添加 1 和乘以 1 。所以，如果你有MSB设置为 1 和位也设置为 1 的其余部分，你将它们翻转（获得32个零），添加 1 （获得 1 ）和 1 终于得到 1 。

Both 4294967295 (a.k.a. UINT_MAX) and -1 have the same binary representation of 0xFFFFFFFF or 32 bits all set to 1. This is because signed numbers are represented using two's complement. A negative number has its MSB (most significant bit) set to 1 and its value determined by flipping the rest of the bits, adding 1 and multiplying by -1. So if you have the MSB set to 1 and the rest of the bits also set to 1, you flip them (get 32 zeros), add 1 (get 1) and multiply by -1 to finally get -1.

这使得它更容易为CPU做数学题，因为它需要为负数没有特别的异常。例如，尝试添加 0xFFFFFFFF的（-1）和 1 。由于只有32位的房间，这会溢出，结果将是 0 如预期

This makes it easier for the CPU to do the math as it needs no special exceptions for negative numbers. For example, try adding 0xFFFFFFFF (-1) and 1. Since there is only room for 32 bits, this will overflow and the result will be 0 as expected.

更多信息请访问：

http://en.wikipedia.org/wiki/Two%27s_complement

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