如何测量std :: unordered_map的内存使用情况 [英] How to measure Memory Usage of std::unordered_map

问题描述

我们知道基于哈希表的容器实现，例如 std :: unordered_map 使用大量内存，但是我不知道多少?

We know that hash table based container implementations like std::unordered_map use a lot memory but I don't know how much is how much?

除了空间复杂度符号外，不考虑容器元素是否是指向更大对象的指针:

Apart from space complexity notations, and not considering if a container element is a pointer to a larger object:

有什么方法可以计算出运行时此类容器使用了多少个字节?

Is there any way to figure out how many bytes is being used by such a container during run-time?

是否有一种方法可以在运行时告诉任何容器使用多少内存?

Is there a way to tell, at runtime, how much memory any container uses?

推荐答案

如果您想获得大致尺寸，我认为 bucket_count()和 max_load_factor()是足够，它给出了当前的铲斗数量和负载系数.

If you want to get a rough size, I think bucket_count() and max_load_factor() is enough, which gives the current count of buckets and the load factor.

理性:

• 如果 load_factor < == 1，则表示 bucket_count()> =映射中的项目，则bucket_count()是内存大小用法.

• If load_factor <= 1, it indicates that bucket_count() >= the items in the map, then bucket_count() is the size of memory usage.

如果 load_factor > 1，则 bucket_count() * load_factor 表示地图中的最大商品.请注意，这是最大大小，而不是实际大小.

If load_factor > 1, then bucket_count() * load_factor indicates the max item in the map. Note this is the max size, not the real size.

因此，粗略的内存使用情况可能看起来像这样:

So for a rough memory usage could look like this:

  unsigned n = mymap.bucket_count();
  float m = mymap.max_load_factor();
  if (m > 1.0) {
    return n * m;
  }
  else {
    return n;
  }

如果要获取准确的内存使用情况，则可能需要计算所有存储桶以查看其中的元素数量:

If you want to get the accurate memory usage, you may need to count all the buckets to see how many elements in it:

  size_t count = 0;
  for (unsigned i = 0; i < mymap.bucket_count(); ++i) {
    size_t bucket_size = mymap.bucket_size(i);
    if (bucket_size == 0) {
      count++;
    }
    else {
      count += bucket_size;
    }
  }

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