std::vector 和多维数组的连续内存

问题描述

我知道标准不会强制std::vector分配连续的内存块，但所有实现都遵守这一点.

I know that the standard does not force std::vector to allocate contiguous memory blocks, but all implementations obey this nevertheless.

假设我想创建一个多维静态数组的向量.为简单起见，考虑 2 个维度，以及一个长度为 N 的向量.也就是说，我希望创建一个包含 N 个元素的向量，例如 int[5].

Suppose I wish to create a vector of a multidimensional, static array. Consider 2 dimensions for simplicity, and a vector of length N. That is I wish to create a vector with N elements of, say, int[5].

我能确定所有 N*5 整数现在在内存中都是连续的吗?这样我原则上就可以通过知道第一个元素的地址来访问所有整数?此实现是否依赖?

Can I be certain that all N*5 integers are now contiguous in memory? So that I in principle could access all of the integers simply by knowing the address of the first element? Is this implementation dependent?

作为参考，我目前在连续内存块中创建二维数组的方式是首先创建一个长度为 N 的 float* 数组(动态)，将所有 N*5 个浮点数分配到一个数组中，然后复制每个数组的地址float* 的第一个数组中的第 5 个元素.

For reference the way I currently create a 2D array in a contiguous memory block is by first making a (dynamic) array of float* of length N, allocating all N*5 floats in one array and then copying the address of every 5th element into the first array of float*.

推荐答案

作为参考，我目前在连续内存块中创建二维数组的方式是首先创建一个长度为 N 的 float* 数组(动态)，将所有 N*5 个浮点数分配到一个数组中，然后复制每个数组的地址第 5 个元素进入 float* 的第一个数组.

For reference the way I currently create a 2D array in a contiguous memory block is by first making a (dynamic) array of float* of length N, allocating all N*5 floats in one array and then copying the address of every 5th element into the first array of float*.

那不是二维数组，而是指针数组.如果你想要一个真正的二维数组，这就是它的完成方式:

That's not a 2D array, that's an array of pointers. If you want a real 2D array, this is how it's done:

float (*p)[5] = new float[N][5];

p [0] [0] = 42;   // access first element
p[N-1][4] = 42;   // access last element

delete[] p;

注意只有一个分配.我可以建议阅读更多关于在 C++ 中使用数组的内容吗?

Note there is only a single allocation. May I suggest reading more about using arrays in C++?

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