在C ++中，我怎么能测试的几个标志与＆QUOT组合之一; |＆QUOT;在一个说法？ [英] In C++, how can I test for one of several flags combined with "|" in one argument?

问题描述

我旁边code：

int main()
{
 OwnSelect(23, FD_READ | FD_WRITE); // <---- Several arguments as one
 return 0;
}

int OwnSelect(SOCKET s, long lNetworkEvents)
{
 // How can i check that FD_READ has been passed?
 if(lNetworkEvents == FD_READ)
 {
  // never here
 }
 return 0;
}

如何检查FD_READ已经过去了不管另一FD已通过与FD_READ。
谢谢！

How can i check that FD_READ has been passed no matter if another FD has been passed with FD_READ. Thanks!

推荐答案

好像你对位的基本位操作在这里错过了。你比特OR FD_READ和FD_WRITE（| =按位OR），从而设置由两个值表示的位，作为一个参数。要检查是否FD_READ获得通过，你需要和lNetworkEvents与FD_READ和检查结果等于FD_READ，像这样：

Seems like you're missing out on a bit of basic bit manipulation here. You're OR'ing FD_READ and FD_WRITE (| = bitwise OR), thereby setting the bits indicated by both values, as a parameter. To check if FD_READ was passed, you need to AND lNetworkEvents with FD_READ and check if the result equals FD_READ, like so:


    如果（FD_READ ==（lNetworkEvents＆放大器; FD_READ））{...}


这当然假设FD_READ和FD_WRITE是注定要这样使用值（即通常不具有重叠位）。

This of course assuming that FD_READ and FD_WRITE are values that were meant to be used this way (i.e. typically don't have overlapping bits).

编辑：固定，wabepper是绝对正确的:)哎呀

edit: fixed, wabepper is absolutely right :) oops!

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