std :: vector元素是否保证是连续的？ [英] Are std::vector elements guaranteed to be contiguous?

问题描述

我的问题很简单：std :: vector元素保证是连续的？按顺序，我可以使用std :: vector的第一个元素的指针作为C数组？

My question is simple: are std::vector elements guaranteed to be contiguous? In order word, can I use the pointer to the first element of a std::vector as a C-array?

如果我的内存很好，C ++标准没有作出这样的保证。然而，std :: vector的要求是，如果元素不是连续的，它几乎是不可能满足的。

If my memory serves me well, the C++ standard did not make such guarantee. However, the std::vector requirements were such that it was virtually impossible to meet them if the elements were not contiguous.

有人可以澄清这一点吗？

Can somebody clarify this?

示例：

std::vector<int> values;
// ... fill up values

if( !values.empty() )
{
    int *array = &values[0];
    for( int i = 0; i < values.size(); ++i )
    {
        int v = array[i];
        // do something with 'v'
    }
}

推荐答案

这是从C ++ 98标准错过了，但后来作为TR的一部分添加。

This was missed from C++98 standard proper but later added as part of a TR. The forthcoming C++0x standard will of course contain this as a requirement.

从n2798（C ++ 0x草稿）：

From n2798 (draft of C++0x):

23.2.6类模板向量[vector]

1向量是支持随机存取迭代器的序列容器。此外，它支持（摊销）
常量时间插入和擦除操作结束;在中间插入和擦除取线性时间。存储
管理是自动处理的，虽然可以提供提示以提高效率。
向量的元素是连续存储的，意味着如果v是一个向量，其中T是某种类型的其他
而不是bool，则它遵守身份& v [n] ==& v [ 0] + n，对于所有0 <= n < v.size（）。

1 A vector is a sequence container that supports random access iterators. In addition, it supports (amortized) constant time insert and erase operations at the end; insert and erase in the middle take linear time. Storage management is handled automatically, though hints can be given to improve efficiency. The elements of a vector are stored contiguously, meaning that if v is a vector where T is some type other than bool, then it obeys the identity &v[n] == &v[0] + n for all 0 <= n < v.size().

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