c++ - 为什么 C++ 不将 INT_MIN 定义为 (1<<31)

Question

我理解 C++ 将 INT_MIN 定义为 (-2147483647 - 1) 的原因，但他们为什么不直接使用 1<<31 呢？既防止溢出又易于理解。

Answer 1

That prevent the overflow and also easy to understand

如果通过左移一个正数试图得到一个负数，它如何防止溢出？ ;)

请记住，有符号整数溢出是未定义行为。根据 C++11 标准的第 5.8/2 段:

The value of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are zero-filled. [...] Otherwise, if E1 has a signed type and non-negative value, and E1×2^E2 is representable in the corresponding unsigned type of the result type, then that value, converted to the result type, is the resulting value; otherwise, the behavior is undefined.

此外，根据第 5/4 段:

If during the evaluation of an expression, the result is not mathematically defined or not in the range of representable values for its type, the behavior is undefined. [...]