问题描述
在中我讨论使用 std :: ifstream 对象转换为 bool 来测试流是否仍处于良好状态。我在Josuttis的书中查看了更多的信息（如果你感兴趣的话，第600页），事实证明 iostream 对象实际上重载 void * 。当流错误（可以隐式转换为 false ）时返回空指针，否则返回非空指针（隐式转换为 true ）。为什么他们只是重载 operator bool ？
In this answer I talk about using a std::ifstream object's conversion to bool to test whether the stream is still in a good state. I looked in the Josuttis book for more information (p. 600 if you're interested), and it turns out that the iostream objects actually overload operator void*. It returns a null pointer when the stream is bad (which can be implicitly converted to false), and a non-null pointer otherwise (implicitly converted to true). Why don't they just overload operator bool?
推荐答案
一个安全bool问题的实例。
This is an instance of the "safe bool" problem.
这里是一篇好文章：。
C ++ 0x可帮助 explicit 转换函数，以及Kristo提到的更改。另请参见。
C++0x helps the situation with explicit conversion functions, as well as the change that Kristo mentions. See also Is the safe-bool idiom obsolete? .
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