Qt's QHash has an interesting feature which allows you to replace a value during iteration of a hashtable:

http://doc.qt.nokia.com/latest/qhash-iterator.html#value

QHash<uint, ServiceRequest*>::iterator i = priv->requests.begin();
while (i != priv->requests.end()) {
  if (i.key() == "Hello")
     i.value() = "Bonjour";
  ++i;
}

In GLib something similar could be done by adding alongside the already existing g_hash_table_iter_remove a g_hash_table_iter_replace.