QuickFix.Message.ExtractBeginString C# (CSharp) Method

        public static string ExtractBeginString(string msgstr)
        {
            int i = 0;
            return ExtractField(msgstr, ref i, null, null).Obj;
        }

        /// <summary>
        /// Constructs a group and stores it in this Message object
        /// </summary>
        /// <param name="grpNoFld">the group's counter field</param>
        /// <param name="msgstr">full message string</param>
        /// <param name="pos">starting character position of group</param>
        /// <param name="fieldMap">full message as FieldMap</param>
        /// <param name="dd">group definition structure from dd</param>
        /// <param name="sessionDataDictionary"></param>
        /// <param name="appDD"></param>
        /// <param name="msgFactory">if null, then this method will use the generic Group class constructor</param>
        /// <returns></returns>
        protected int SetGroup(
            StringField grpNoFld, string msgstr, int pos, FieldMap fieldMap, DataDictionary.IGroupSpec dd,
            DataDictionary.DataDictionary sessionDataDictionary, DataDictionary.DataDictionary appDD, IMessageFactory msgFactory)
        {
            int   grpEntryDelimiterTag = dd.Delim;
            int   grpPos = pos;
            Group grp    = null; // the group entry being constructed

            while (pos < msgstr.Length)
            {
                grpPos = pos;
                StringField f = ExtractField(msgstr, ref pos, sessionDataDictionary, appDD);
                if (f.Tag == grpEntryDelimiterTag)
                {
                    // This is the start of a group entry.

                    if (grp != null)
                    {
                        // We were already building an entry, so the delimiter means it's done.
                        fieldMap.AddGroup(grp, false);
                        grp = null; // prepare for new Group
                    }

                    // Create a new group!
                    if (msgFactory != null)
                    {
                        grp = msgFactory.Create(Message.ExtractBeginString(msgstr), Message.GetMsgType(msgstr), grpNoFld.Tag);
                    }

                    //If above failed (shouldn't ever happen), just use a generic Group.
                    if (grp == null)
                    {
                        grp = new Group(grpNoFld.Tag, grpEntryDelimiterTag);
                    }
                }
                else if (!dd.IsField(f.Tag))
                {
                    // This field is not in the group, thus the repeating group is done.

                    if (grp != null)
                    {
                        fieldMap.AddGroup(grp, false);
                    }
                    return(grpPos);
                }

                if (grp == null)
                {
                    // This means we got into the group's fields without finding a delimiter tag.
                    throw new GroupDelimiterTagException(grpNoFld.Tag, grpEntryDelimiterTag);
                }

                // f is just a field in our group entry.  Add it and iterate again.
                grp.SetField(f);
                if (dd.IsGroup(f.Tag))
                {
                    // f is a counter for a nested group.  Recurse!
                    pos = SetGroup(f, msgstr, pos, grp, dd.GetGroupSpec(f.Tag), sessionDataDictionary, appDD, msgFactory);
                }
            }

            return(grpPos);
        }