Table Iterators

In the examples up to now, the code, which wanted to get values from the table, knew what the keys were. It's also useful to be able to write generic code which can operate on a table without knowing the keys. ``Table iterators'' (``iterators'', for short) are used for this.

An iterator is an abstraction of a pointer to a particular table entry. Iterators are analogous to the DIR * pointers used by the POSIX opendir(), readdir(), closedir(), and similar functions, to Perl hash tables' each(), keys(), and values(), and to the C++ Standard Template Library's forward iterators.

At any time, the entries in a table may be considered to be in some arbitrary (implementation-defined) order; an iterator may be used to walk through some or all of the table entries in this order. This order is guaranteed to remain unchanged for any given table, so long as no changes are made to that table, so long as no Util_TableSet*(), Util_TableSet*Array(), Util_TableSetGeneric(), Util_TableSetGenericArray(), Util_TableSetString(), or Util_TableDeleteKey() calls are made on that table (making such calls on other tables doesn't matter). The order may change if there is any change in the table, and it may differ even between different tables with identical key/value contents (including those produced by Util_TableClone()).^part178

Any change in the table also invalidates all iterators pointing anywhere in the table; using any such iterator is an error. Multiple iterators may point into the same table; they all use the same order, and (unlike in Perl) they're all independent.

The detailed function description in the Reference Manual for Util_TableItQueryKeyValueInfo() has an example of using an iterator to print out all the entries in a table.