数组向量的内存布局是什么? [英] What is the memory layout of a vector of arrays?

问题描述

类型为Vec<[f3; 5]>的变量是作为一个连续数组(为Vec::len() * 5 * sizeof(f32)个字节)存储还是作为指针的Vec存储?

Are variables of type Vec<[f3; 5]> stored as one contiguous array (of Vec::len() * 5 * sizeof(f32) bytes) or is it stored as a Vec of pointers?

推荐答案

Vec<T>的内容与self.capacity() * std::mem::size_of::<T>()字节一样，是单个堆分配(与T无关). (Vec求和，这是Vec<T>的全部要点，而不是Box<[T]>，因此在此计算中，容量而不是长度是要紧的.)实际的Vec<T>本身需要三个词(

The contents of a Vec<T> is, regardless of T, a single heap allocation, of self.capacity() * std::mem::size_of::<T>() bytes. (Vec overallocates—that’s the whole point of Vec<T> instead of Box<[T]>—so it’s the capacity, not the length, that matter in this calculation.) The actual Vec<T> itself takes three words (24 bytes on a 64-bit machine).

[f32; 5]只是一块内存，其中包含五个32位浮点数，没有间接寻址；这是二十个字节(因此 std::mem::size_of::<[f32; 5]>() == 20 ).

[f32; 5] is just a chunk of memory containing five 32-bit floating-point numbers, with no indirection; this comes to twenty bytes (hence std::mem::size_of::<[f32; 5]>() == 20).

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