CODEWITHSUNDEEP
c#hashgethashcodeiequalitycomparer
Chavoosh
Chavoosh

Reputation: 445

Definition of GetHashCode() in C#

Dictionary in C# uses GetHashCode() to retrieve hash code of a given key. I walk through whole of the Dictionary Class, but there is not any definition for GetHashCode() function. It is bothering me and I don't know how I can find definition of it in this class!

Assume I am using Dictionary<int,int> a = new Dictionary<int,int>(), now what is the hash code of a given key in this structure? (e.g. suppose this: a.Add(123,43). what is the hash code of this key, if number of buckets being 50)

This is a part of Insert() function of Dictionary class.

private void Insert(TKey key, TValue value, bool add)
    {
        int freeList;
        if (key == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
        }
        if (this.buckets == null)
        {
            this.Initialize(0);
        }
        int num = this.comparer.GetHashCode(key) & 0x7fffffff;
        int index = num % this.buckets.Length;

Upvotes: 0

Views: 323

Answers (2)

usr
usr

Reputation: 171178

If you don't specify an IEqualityComparer, Dictionary uses EqualityComparer<T>.Default. This is a comparer that will just call object.GetHashCode on the given argument. So look at Int32.GetHashCode.

Upvotes: 3

MarcinJuraszek
MarcinJuraszek

Reputation: 125620

GetHashCode is implemented on your TKey type, not on the Dictionary class.

For int.GetHashCode(), which your example uses, it's defined as:

public override int GetHashCode()
{
    return this;
}

Number of backets has nothing to do with the hashcode value.

Upvotes: 2

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