c++ - std::initializer_list 和元素的求值顺序

Question

逗号 ( , ) 是 std::initializer_list 中的序列点吗？

---

示例:这是否是 UB:

#include <vector>

int main() 
{
    auto nums = []
    {
        static unsigned x = 2;
        return ( x++ % 2 ) + 1;
    };

    std::vector< int > v{ nums(), nums(), nums(), nums(), nums() };
    // not sure if this is different: (note the additional brackets)
    // std::vector< int > v({ nums(), nums(), nums(), nums(), nums() });
    for( auto i : v )
    {
        std::cout << i;
    }

    return 0;
}

Answer 1

根据 C++11 § 8.5.4 [dcl.init.list] 第 4 段:

4 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.

据我所知，GCC 4.8.1 有一个与初始值设定项评估相关的错误。我在这里描述了

http://cpp.forum24.ru/?1-3-0-00000063-000-0-0-1378892425

虽然文本是用俄语写的，但可以使用谷歌翻译等简单地将其翻译成英语。