C++ (~0L) 是什么意思？
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What does (~0L) mean?
提问by Noitidart
I'm doing some X11 ctypes coding, I don't know C but need some help understanding this.
我正在做一些 X11 ctypes 编码，我不知道 C，但需要一些帮助来理解这一点。
In the C code below (might be C++ im not sure) we see (~0L)what does that mean? In Javascript and Python ~0means -1.
在下面的 C 代码（可能是 C++ 我不确定）中，我们看到(~0L)了这意味着什么？在 Javascript 和 Python 中的~0意思是-1.
812 int result = GetProperty(window, property_name,
813 (~0L), // (all of them)
814 &type, &format, &num_items, &properties);
Thanks
谢谢
回答by Mark Ransom
0Lis a longinteger 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 longinteger with all the bits set to one.
0L是一个long整数值，所有位都设置为零 - 这通常是0. 该~方法反转所有位，这让你有一个long与所有设置为一个位整数。
In two's complement arithmetic (which is almost universal) a signed value with all bits set to one is -1.
在二进制补码算法（几乎是通用的）中，所有位都设置为 1 的有符号值是-1。
The reason for using ~0Linstead of -1Lis 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.
使用~0L而不是的原因-1L是为了更清楚地了解意图 - 它根本不打算用作数字，而是用作位的集合。
回答by Bill
Bitwise compliment of zero of long type.
长型零的按位补码。
