Use byte[] as key in dictionary

Question

I need to use a byte[] as a key in a Dictionary. Since byte[] doesn\'t override the default GetHashCode method, two sepa

Answer 1

By default byte[] will be compared by reference which is not what you want in this case. What you need to do is specify a custom IEqualityComparer and do the comparison you want.

For example

public class ByteArrayComparer : IEqualityComparer {
  public bool Equals(byte[] left, byte[] right) {
    if ( left == null || right == null ) {
      return left == right;
    }
    return left.SequenceEqual(right);
  }
  public int GetHashCode(byte[] key) {
    if (key == null)
      throw new ArgumentNullException("key");
    return key.Sum(b => b);
  }
}

Then you can do

var dict = new Dictionary(new ByteArrayComparer());

Solution for 2.0

public class ByteArrayComparer : IEqualityComparer {
  public bool Equals(byte[] left, byte[] right) {
    if ( left == null || right == null ) {
      return left == right;
    }
    if ( left.Length != right.Length ) {
      return false;
    }
    for ( int i= 0; i < left.Length; i++) {
      if ( left[i] != right[i] ) {
        return false;
      }
    }
    return true;
  }
  public int GetHashCode(byte[] key) {
    if (key == null)
      throw new ArgumentNullException("key");
    int sum = 0;
    foreach ( byte cur in key ) {
      sum += cur;
    }
    return sum;
  }
}