c++ - 逗号分隔变量定义中的先序关系

Question

让我们从以下示例代码开始:

int a = 0, b = a++, c = a;

a++ 是否在 a 之前(在 c = a 内)？ a++ 和 a 似乎符合完整表达式的条件，并且根据 cppreference (规则 1)，答案应该是肯定的。但我不确定。

Answer 1

是的。作为Brian指出，这不是逗号运算符，而是一个init-declarator-list。从 [dcl.decl] 我们有:

Each init-declarator in a declaration is analyzed separately as if it was in a declaration by itself.

用脚注阐明:

A declaration with several declarators is usually equivalent to the corresponding sequence of declarations each with a single declarator. That is

T D1, D2, ... Dn;

is usually equivalent to

T D1; T D2; ... T Dn;

where T is a decl-specifier-seq and each Di is an init-declarator.

有两个异常(exception)，一个是隐藏类型的名称，一个是auto，两者都不适用。所以最终，您拥有的代码完全等同于:

int a = 0;
int b = a++;
int c = a;

您应该首先写下它，因为它不需要搜索标准来确保您做的事情是有效的!