Hashtables

Well I was looking for a hash-map in C++ since doing something like

myMap[i];

Where myMap is an std::map<> takes logarithmic look up.

So after some looking around I did manage to find that there were hash-maps for C++, but after that I had to do some more searching to see what libraries I needed to include in order to use them.

Below is a little program that just prints the integers 1 to 10 followed by hello world, that makes use of a hash-map.

#include<iostream>
#include<ext/hash_map>
#include<string>
using namespace std;
using namespace __gnu_cxx;

int main()
{
 hash_map<int,int> myhash;
 for(int i=0;i<10;i++)
     myhash[i]=i+1;
 for(typeof(myhash.begin()) i=myhash.begin();i!=myhash.end();i++)
     cout<<i->second<<' ';
 cout<<"hello world\n";
 return 0;
}

Certainly not the most user friendly stuff to type at the beginning but I suppose it is worth it. I should mention that when I wrote the second for loop I had no idea if it would compile or not since I didn't know that you could use iterators on hash_maps. Also unlike std::map, __gnu_cxx::hash_map does not store the keys in an ordered fashion, just something to be aware of.

As a side note, if you didn't add the line

using namespace __gnu_cxx;

you would have to type

__gnu_cxx::hash_map<Tyep&key,Type&value>;

This should be obvious but you never know when/if you'll one day forget.