我可以投一个std ::数组切片？或者是有什么我可以用呢？ [英] Can I cast a std::array to slice? Or is there anything else I can use instead?

问题描述

这是不确定的行为？

std::array<int, 5> x = {3, 5, 1, 2, 3};
std::array<int, 3>& y = *reinterpret_cast<std::array<int, 3>*>(&x[1]);
for(int i = 0; i != 3; i++) {
    std::cout << y[i] << "\n";
}

也许是的，但我真的觉得应该有一个安全办法切片的std ::阵列秒。

编辑：以下拉狄克的建议：

template<unsigned N, unsigned start, unsigned end, typename T>
std::array<T, end - start>& array_slice(std::array<T, N>& x)
{
    static_assert(start <= end, "start <= end");
    static_assert(end <= N-1, "end <= N");
    return *reinterpret_cast<std::array<T, end - start>*>(&x[start]);
}

编辑：确定，我决定，我很不满意的std ::阵列和将移动到别的东西，任何想法？

Ok, I decided that I'm unhappy with std::arrays and will move to something else, any ideas?

推荐答案

是的，这是不确定的行为。你把同一类型和 reinter pret_cast ING到另一个。事实上，使用 reinter pret_cast的应该是一个大红旗此处有怪物！

Yes, that is undefined behavior. You're taking one type and reinterpret_casting it to another. Indeed, the use of the reinterpret_cast should be a big red flag for "here there be dragons!"

对于数组切片，这是不会发生的。 A 的std ::阵列包含的值;这片将包含的引用的该阵列的一部分。因此，它不会是一个的std ::阵列。你可以的复制的阵列的片，但不能使用的std ::阵列。您需要使用的std ::矢量，因为它允许构造函数从一个值范围的通话，以及建筑。记住：的std ::阵列只是围绕一个C数组一个更好的包装

As for slicing arrays, that's not going to happen. A std::array contains values; a slice of this would contain references to part of that array. And therefore, it would not be a std::array. You can copy slices of arrays, but not using std::array. You would need to use std::vector, since it allows the calling of constructors, as well as construction from a range of values. Remember: std::array is just a nicer wrapper around a C-style array.

该委员会正在研究的模板 ARRAY_REF＆LT; T＆GT; 类，而这正是它说：到类型的数组中某一段参考 T 。这可能是一个常规的C风格的数组，的std ::矢量，一个的std ::阵列，或者只是一些内存分配与新T [] 。有的类已经的一些库实现，但没有什么是尚未标准化。

The committee is looking into a template array_ref<T> class, which is exactly what it says: a reference to some segment of an array of type T. This could be a regular C-style array, a std::vector, a std::array, or just some memory allocated with new T[]. There are some library implementations of the class already, but nothing is standardized yet.

继拉狄克的建议：

躲在一个函数未定义行为的不让它定义的行为的。你可以尝试pretend它不是不确定的，但它仍然是。那一刻您使用 reinter pret_cast ，你心甘情愿地放弃生活在C ++ - 土地

Hiding the undefined behavior in a function does not make it defined behavior. You can try to pretend that it isn't undefined, but it still is. The moment you use that reinterpret_cast, you willingly give up living in C++-land.

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