internal static class StringFunctions
{
    //------------------------------------------------------------------------------------
    //  This method allows replacing a single character in a string, to help convert
    //  C++ code where a single character in a character array is replaced.
    //------------------------------------------------------------------------------------
    internal static string ChangeCharacter(string sourcestring, int charindex, char changechar)
    {
        return (charindex > 0 ? sourcestring.Substring(0, charindex) : "")
            + changechar.ToString() + (charindex < sourcestring.Length - 1 ? sourcestring.Substring(charindex + 1) : "");
    }

    //------------------------------------------------------------------------------------
    //  This method simulates the classic C string function 'isxdigit' (and 'iswxdigit').
    //------------------------------------------------------------------------------------
    internal static bool IsXDigit(char character)
    {
        if (char.IsDigit(character))
            return true;
        else if ("ABCDEFabcdef".IndexOf(character) > -1)
            return true;
        else
            return false;
    }

    //------------------------------------------------------------------------------------
    //  This method simulates the classic C string function 'strchr' (and 'wcschr').
    //------------------------------------------------------------------------------------
    internal static string StrChr(string stringtosearch, char chartofind)
    {
        int index = stringtosearch.IndexOf(chartofind);
        if (index > -1)
            return stringtosearch.Substring(index);
        else
            return null;
    }

    //------------------------------------------------------------------------------------
    //  This method simulates the classic C string function 'strrchr' (and 'wcsrchr').
    //------------------------------------------------------------------------------------
    internal static string StrRChr(string stringtosearch, char chartofind)
    {
        int index = stringtosearch.LastIndexOf(chartofind);
        if (index > -1)
            return stringtosearch.Substring(index);
        else
            return null;
    }

    //------------------------------------------------------------------------------------
    //  This method simulates the classic C string function 'strstr' (and 'wcsstr').
    //------------------------------------------------------------------------------------
    internal static string StrStr(string stringtosearch, string stringtofind)
    {
        int index = stringtosearch.IndexOf(stringtofind);
        if (index > -1)
            return stringtosearch.Substring(index);
        else
            return null;
    }

    //------------------------------------------------------------------------------------
    //  This method simulates the classic C string function 'strtok' (and 'wcstok').
    //  Note that the .NET string 'Split' method cannot be used to simulate 'strtok' since
    //  it doesn't allow changing the delimiters between each token retrieval.
    //------------------------------------------------------------------------------------
    private static string activestring;
    private static int activeposition;
    internal static string StrTok(string stringtotokenize, string delimiters)
    {
        if (stringtotokenize != null)
        {
            activestring = stringtotokenize;
            activeposition = -1;
        }

        //the stringtotokenize was never set:
        if (activestring == null)
            return null;

        //all tokens have already been extracted:
        if (activeposition == activestring.Length)
            return null;

        //bypass delimiters:
        activeposition++;
        while (activeposition < activestring.Length && delimiters.IndexOf(activestring[activeposition]) > -1)
        {
            activeposition++;
        }

        //only delimiters were left, so return null:
        if (activeposition == activestring.Length)
            return null;

        //get starting position of string to return:
        int startingposition = activeposition;

        //read until next delimiter:
        do
        {
            activeposition++;
        } while (activeposition < activestring.Length && delimiters.IndexOf(activestring[activeposition]) == -1);

        return activestring.Substring(startingposition, activeposition - startingposition);
    }
}