c - 是否定义了 _Bool 递增？

Question

C 标准将 _Bool 定义为包含 0 或 1 的无符号类型。如果 _Bool 类型的值 1 递增，据我所知，有两个选项:

该值在 1 到 0 之间环绕

该值增加到 2，它是非零值，因此在转换回 _Bool

时变为 1。

在我的系统上的 GCC 和 Clang 上，行为似乎是后者。这是否由标准明确定义？

Answer 1

来自 C 标准(6.3.1.2 boolean 类型)

1 When any scalar value is converted to _Bool, the result is 0 if the value compares equal to 0; otherwise, the result is 1.

例如 6.5.3.1 前缀自增和自减运算符

2 The value of the operand of the prefix ++ operator is incremented. The result is the new value of the operand after incrementation. The expression ++E is equivalent to (E+=1).

最后 6.5.16.2 复合赋值

3 A compound assignment of the form E1 op = E2 is equivalent to the simple assignment expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with respect to an indeterminately-sequenced function call, the operation of a compound assignment is a single evaluation. If E1 has an atomic type, compound assignment is a read-modify-write operation with memory_order_seq_cst memory order semantics.

注意(6.3 转换)

— The rank of _Bool shall be less than the rank of all other standard integer types.

因此在表达式中使用的类型 _Bool 被转换为具有更高等级的其他类型。