运算符优先级（bool 之前的 void*？）
在回答这个问题时，我做了一些研究，这确实让我感到困惑。
我注意到成功打开的两个 ifstream 不相等，但失败的两个 ifstream 相等。 首先我查看了 cplusplus.com。 operator ! 返回badbit 和failbit。我认为与此相反的仍然是返回这两个位的状态，但是翻转了。
- 错误，因为两次成功的调用并不相等。
然后我认为这是一个会返回某些内容的 operator bool 。因此，我尝试从 ifstream 回溯并找到 istream::operator bool()，它返回 _Ok。
- 但是仍然错误，这似乎根本没有被调用（也不可能被调用，因为两个成功的调用仍然不相等）。
所以我改变了我的方法并检查了 Visual Studio 中的反汇编。我发现了什么？if (file0 != file1) { 不会调用运算符 bool()，而是调用运算符 void* () （或者实际上是__imp_std::ios_base::operator void *）。
所以我的问题是..
- 在尝试将其转换为指针值之前，是否不应该调用任何找到的运算符 bool () ？
- 是不是我错过了一些
operator bool()，而它又调用了operator void*？ 这是一些我不理解的优化吗？
或者我完全错了，C++ 实际上认为在此比较中
void*比bool更好匹配？
When answering this question I made some research which really confuses me.
I noticed that two ifstreams that succesfully open are not equal but two ifstreams that fail are.
At first i checked cplusplus.com. The operator ! returns the status of the badbit and failbit. I think that the opposite of this would still be to return the status of these two bits, but flipped.
- Wrong, because two succesful calls are not equal.
So then I figured it was an operator bool somewhere that would return something. So I tried to backtrack from ifstream and found the istream::operator bool(), which is returning _Ok.
- Still wrong however, this doesn't seem to be called at all (and couldn't be, since the two successful calls are still not equal).
So I changed my approach and checked the disassembly from Visual Studio. And what do I find?if (file0 != file1) { doesn't call the operator bool(), but rather the operator void* () (or really __imp_std::ios_base::operator void *).
So the questions I have are..
- Shouldn't any
operator bool ()found be called before trying to casting it to pointer values? - Is it some
operator bool()I missed that in turn is calling theoperator void*? Is this some optimizing that I don't understand?
Or am I completely wrong in that C++ actually thinks that
void*is a better match thanboolin this comparison?
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（1）
1.) 不能多次重载但返回类型不同。
2.) 是的，
operator!返回 badbit/failbit，但是operator!与operator!=完全不同，后者是你正在使用。1.) You cannot overload multiple times but with different return types.
2.) Yes,
operator!returns the badbit/failbit, butoperator!is something entirely different fromoperator!=, which is the one you are using.