c++ - How to measure Memory Usage of std::unordered_map -


we know hash table based container implementations std::unordered_map use lot memory don't know how how much?

apart space complexity notations, , not considering if container element pointer larger object:

is there way figure out how many bytes being used such container during run-time?

is there way tell, @ runtime, how memory any container uses?

if want rough size, think bucket_count() , max_load_factor() enough, gives current count of buckets , load factor.

rational:

  • if load_factor <= 1, indicates bucket_count() >= items in map, bucket_count() size of memory usage.

  • if load_factor > 1, bucket_count() * load_factor indicates max item in map. note max size, not real size.

so rough memory usage this:

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

if want accurate memory usage, may need count buckets see how many elements in it:

  size_t count = 0;   (unsigned = 0; < 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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