Question

Recently I have been reading up on some of the flaws with the Java substring method – specifically relating to memory, and how java keeps a reference to the original string. Ironically I am also developing a server application that uses C# .Net’s implementation of substring many tens of times in a second. That got me thinking…

1. Are there memory issues with the C# (.Net) string.Substring?
2. What is the performance like on string.Substring? Is there a faster way to split a string based on start/end position?

Answer 1

Looking at .NET’s implementation of String.Substring, a substring does not share memory with the original.

private unsafe string InternalSubString(int startIndex, int length, bool fAlwaysCopy)
{
    if (((startIndex == 0) && (length == this.Length)) && !fAlwaysCopy)
    {
        return this;
    }

    // Allocate new (separate) string
    string str = FastAllocateString(length);

    // Copy chars from old string to new string
    fixed (char* chRef = &str.m_firstChar)
    {
        fixed (char* chRef2 = &this.m_firstChar)
        {
            wstrcpy(chRef, chRef2 + startIndex, length);
        }
    }
    return str;
}