std :: pair中的初始化列表 [英] Initializer list inside std::pair

问题描述

此代码:

#include <iostream>
#include <string>

std::pair<std::initializer_list<std::string>, int> groups{ { "A", "B" }, 0 };

int main()
{
    for (const auto& i : groups.first)
    {
        std::cout << i << '\n';
    }
    return 0;
}

编译但返回段错误.为什么?

compiles but returns segfault. Why?

在gcc 8.3.0和在线编译器上进行了测试.

Tested on gcc 8.3.0 and on online compilers.

推荐答案

std :: initializer_list 并不意味着要存储，它仅用于...很好的初始化.在内部，它仅存储指向第一个元素和大小的指针.在您的代码中， std :: string 对象是临时对象，而 initializer_list 既不拥有它们的所有权，也不延长其寿命，也不复制它们(因为它不是容器)，因此它们在创建后立即超出范围，但是您的 initializer_list 仍然保留指向它们的指针.这就是为什么您会遇到细分错误.

std::initializer_list is not meant to be stored, it is just meant for ... well initialization. Internally it just stores a pointer to the first element and the size. In your code the std::string objects are temporaries and the initializer_list neither takes ownership of them, neither extends their life, neither copies them (because it's not a container) so they go out of scope immediately after creation, but your initializer_list still holds a pointer to them. That is why you get segmentation fault.

要存储，您应该使用一个容器，例如 std :: vector 或 std :: array .

For storing you should use a container, like std::vector or std::array.

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