为什么无效套接字在 WinSock2.h (c++) 中定义为 ~0?
在WinSock2.h中，invalid socket和socket error是这样定义的?这有什么意义吗?
In WinSock2.h, the invalid socket and socket error are defined as these? Is there any significance to this?
#define INVALID_SOCKET (SOCKET)(~0)
#define SOCKET_ERROR (-1)
推荐答案
在二进制补码系统上(Windows 总是二进制补码)，~0 等于 -1，所以对编译器没有意义.
On a two's complement system (and Windows is always two's complement), ~0 is equal to -1, so there's no significance to the compiler.
可能对读者有意义:~0 强调它是一个所有位都设置的值，而 -1 强调它是一个小于 0 的值 1.
There may be a significance to the reader: ~0 emphasizes that it's a value with all bits set, whereas -1 emphasizes that it's a value 1 less than 0.
旁白:
在不是二进制补码的系统上，假设 SOCKET 是无符号类型，通常 错误 写成 (SOCKET)(~0).原因是在这样的系统上，~0 不代表值 -1，它是 INT_MIN、负零或陷阱表示之一.因此，它不一定会转换为类型 SOCKET 作为所有位为零的值，而是将转换为 INT_MAX+2、0 或goodness-knows-what(也许是所有位设置的值).
On a system which is not two's complement, and assuming that SOCKET is an unsigned type, it is generally wrong to write (SOCKET)(~0). The reason is that on such systems, ~0 does not represent the value -1, it's one of INT_MIN, negative zero, or a trap representation. Hence it will not necessarily convert to type SOCKET as the value with all bits zero, rather it will convert as INT_MAX+2, 0, or goodness-knows-what (perhaps the value with all bits set).
所以通常你应该用 -1 初始化无符号类型以获得所有位设置的值.你可以使用UINT_MAX，或~0UL，或类似的，如果你知道你正在处理的无符号类型.但这并不值得，因为 -1 适用于所有无符号类型.
So generally you should initialize unsigned types with -1 to get the value with all bits set. You could use UINT_MAX, or ~0UL, or similar, if you know which unsigned type you're dealing with. But it's not worth it, because -1 works for all unsigned types.
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