Why does .NET create new substrings instead of pointing into existing strings?

Question

From a brief look using Reflector, it looks like String.Substring() allocates memory for each substring. Am I correct that this is the case? I thought that woul

Answer 1

Each string has to have it's own string data, with the way that the String class is implemented.

You can make your own SubString structure that uses part of a string:

public struct SubString {

   private string _str;
   private int _offset, _len;

   public SubString(string str, int offset, int len) {
      _str = str;
      _offset = offset;
      _len = len;
   }

   public int Length { get { return _len; } }

   public char this[int index] {
      get {
         if (index < 0 || index > len) throw new IndexOutOfRangeException();
         return _str[_offset + index];
      }
   }

   public void WriteToStringBuilder(StringBuilder s) {
      s.Write(_str, _offset, _len);
   }

   public override string ToString() {
      return _str.Substring(_offset, _len);
   }

}

You can flesh it out with other methods like comparison that is also possible to do without extracting the string.