修复 bool 相关的示例代码 - #80
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archibate
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Feb 26, 2025
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docs/undef.md
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| ```cpp | ||
| char c = 0; | ||
| bool b = *(bool *)&c; // 可以，b = false |
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为什么把原来的代码删除了？
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原来的写法导致 UB。你觉得应该保留吗？
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你是说 bool b = *(bool *)&c; 是UB？为什么？据我所知char和任意类型的“类型双关”都是允许的，bool和char当然也是可以“类型双关”的。
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你是说 bool b = *(bool *)&c; 是UB？为什么？据我所知char和任意类型的“类型双关”都是允许的，bool和char当然也是可以“类型双关”的。
这里的类型双关是单向的。只能通过 char 泛左值访问 bool 对象，但不能反过来。是否有什么资料导致你认为类型双关是双向的呢？
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Fixes #74.
严格来说标准并未要求 sizeof(bool) == 1，并且标准允许字节有更多的位。更正后的写法只是适用于绝大多数平台。