.. efun:: string traceprefix(string prefix)
  string traceprefix(int dummy)
  :include: <trace.h>

  If called with a string, only objects matching this prefix will be traced. The string must not contain a leading "/" because the object names are stored internally without it. If called with a number, the traceprefix will be ignored and all objects will be traced. Returns the last traceprefix or 0 if there wasn't any.

  :master:`valid_trace` is called with ``("traceprefix", prefix)`` as arguments to verify the use of this efun.

  .. usage::

    The following example shows the basics of how to set up (and later remove) a trace::

      object obj;
      string prefix;
      obj = find_player("wessex");
      prefix = object_name(obj);
      prefix = prefix[1..]; // cut off the leading "/"
      traceprefix(prefix);
        // From here on, only code in the object "std/player#69"
        // will be traced.
        //
      trace(TRACE_CALL | TRACE_CALL_OTHER | TRACE_RETURN | TRACE_ARGS);
      ...
      trace(TRACE_NOTHING);

  :history 3.2.9 changed: passes :arg:`prefix` to the :master:`valid_trace` apply as well.

  .. seealso:: :efun:`trace`