c++ - initializer_list c++11 中的评估顺序

Question

在下面的代码中，是否要求在 f2 之前调用 f1(或反之亦然)，还是未指定？

int f1();
int f2();

std::initializer_list<int> list { f1(), f2() };

Answer 1

这是 C++ 标准的一个有趣的角落，其中执行顺序定义明确。第 8.5.4 节 [dcl.init.list]，第 4 段:

Within the initializer-list of a braced-init-list, the initializer-clauses, including any that result from pack expansions (14.5.3), are evaluated in the order in which they appear. That is, every value computation and side effect associated with a given initializer-clause is sequenced before every value computation and side effect associated with any initializer-clause that follows it in the comma-separated list of the initializer-list.

因此在初始化列表中，函数调用是从左到右求值的。