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

Answer 1

是的。正如指出的那样，这不是逗号运算符，而是 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.

用脚注澄清：

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.

有两个例外，一个是隐藏类型的名称，另一个是 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;

你应该首先写下哪个，因为它不需要搜索标准来确保你做的事情有效！

逗号分隔变量定义中的先序关系

Sequence-before relation in comma-separated variable definitions

c++

operator-precedence