是什么（〜0L）是什么意思？ [英] What does (~0L) mean?

问题描述

我做了一些X11 ctypes的编码，我不知道C，但需要一些帮助理解这一点。

I'm doing some X11 ctypes coding, I don't know C but need some help understanding this.

在下面的C code（可能是C ++林不知道）我们看到（〜0L）这是什么意思？在Javascript和Python 0〜办法 1 。

In the C code below (might be C++ im not sure) we see (~0L) what does that mean? In Javascript and Python ~0 means -1.

812   int result = GetProperty(window, property_name,
813                            (~0L), // (all of them)
814                            &type, &format, &num_items, &properties);

感谢

推荐答案

0L 是一个长的整数值所有位设置为零 - 这通常是的定义0 。在〜表示反转所有位，这让您与设置为1的所有位长整数。

0L is a long integer value with all the bits set to zero - that's generally the definition of 0. The ~ means to invert all the bits, which leaves you with a long integer with all the bits set to one.

在补运算（这几乎是普遍的）一个符号值均设置为1所有位为 1 。

In two's complement arithmetic (which is almost universal) a signed value with all bits set to one is -1.

之所以使用〜0L 而不是 -1L 是要对意图更加清晰 - 它并不意味着被用作一个数在所有的，而是作为位的集合

The reason for using ~0L instead of -1L is to be clearer about the intent - it's not meant to be used as a number at all, but rather as a collection of bits.

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