What is the best way to use a HashMap in C

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I'm aware that STL offers a HashMap API, but I can't locate any excellent and detailed documentation with examples.

Any good examples would be much appreciated.
Jun 9 in C++ by Nicholas
• 5,020 points
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1 answer to this question.

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The ordered and unordered map containers (std::map and std::unordered map) are included in the standard library. 

The items in an ordered map are sorted by key, and insert and access are in O (log n). 

For ordered maps, the standard library often use red black trees. 

However, this is only an implementation detail. 

Insert and access are in O in an unordered map (1). 

It is simply another term for a hashtable.

An illustration using (ordered) std::map:

#include <map>
#include <iostream>
#include <cassert>

int main(int argc, char **argv)
{
  std::map<std::string, int> m;
  m["hello"] = 23;
  // check if key is present
  if (m.find("world") != m.end())
    std::cout << "map contains key world!\n";
  // retrieve
  std::cout << m["hello"] << '\n';
  std::map<std::string, int>::iterator i = m.find("hello");
  assert(i != m.end());
  std::cout << "Key: " << i->first << " Value: " << i->second << '\n';
  return 0;
}

Output:

23
Key: hello Value: 23

If you require ordering in your container and don't mind the O(log n) runtime, use std::map.

answered Jun 10 by Damon
• 4,960 points

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