c++ - 我可以在运行时检查内置类型吗？

Question

例如，

如果我写:

char c = CHAR_MAX;
c++;

我能否知道“c++”的结果是 int 还是 char，以便我确定它是否不是溢出？

Answer 1

我不知道你所说的“运行时检查”是什么意思，但我可以肯定地告诉你，c++ 会产生 char 类型的纯右值，并且c 始终是 char。 c 永远不会转换为 int。

根据 [expr.post.incr]/1 :

The value of a postfix ++ expression is the value of its operand. [ Note: The value obtained is a copy of the original value — end note ] The operand shall be a modifiable lvalue. The type of the operand shall be an arithmetic type other than cv bool, or a pointer to a complete object type. The value of the operand object is modified by adding 1 to it. The value computation of the ++ expression is sequenced before the modification of the operand object. With respect to an indeterminately-sequenced function call, the operation of postfix ++ is a single evaluation. [ Note: Therefore, a function call shall not intervene between the lvalue-to-rvalue conversion and the side effect associated with any single postfix ++ operator. — end note ] The result is a prvalue. The type of the result is the cv-unqualified version of the type of the operand. If the operand is a bit-field that cannot represent the incremented value, the resulting value of the bit-field is implementation-defined. See also [expr.add] and [expr.ass].

如 Nikos C. 所述在评论中，您应该在递增之前检查是否 c == CHAR_MAX。有关检查签名溢出的更多信息，请参阅 Detecting signed overflow in C/C++ .