空矢量的开销成本是多少？ [英] What is the overhead cost of an empty vector?

问题描述

具有空向量vs具有指向向量的指针的内存开销是多少？

选项A：

  std :: vector< int> v; 
  

选项B：

  std :: vector< int> * v = NULL; 
 

我相信选项B需要1个32位指针（假设这里为32位）


解决方案

对于问题：这取决于实现。对于MSVC 7.1，这是：

  std :: cout< sizeof（std :: vector< int>）< std :: endl; 
  

给我16.（3指针：容量的开始，结束和结束，加上一个分配器）

但是应注意指向矢量的指针有较大的开销：

$ b $

>

What is the memory overhead of having an empty vector vs having a pointer to a vector?

Option A:

std::vector<int> v;

Option B:

std::vector<int> *v = NULL;

I believe that option B takes 1 32 bit pointer (assuming 32 bit here) How much memory does the empty 'v' take up?

解决方案

As for the question as asked: It depends on the implementation. With MSVC 7.1 this:

std:: cout << sizeof(std::vector<int>) << std::endl;

gives me 16. (3 pointers: begin, end, and end of capacity, plus an allocator)

However it should be noted that the pointer-to-vector has a larger overhead:

• in both time and space in the non-empty case
• in complexity in all cases.

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