Cursors are used to read messages that are not necessarily at the front of the queue. Cursors can be application-defined or implied, depending on the development platform you are using.
Using any number of application-defined cursors, C applications can navigate through a queue. Each cursor is independent of all other cursors, including those generated by other applications. Moving one cursor has no effect on where another cursor points.
ActiveX applications cannot use multiple, application-defined cursors. They have a single, implied cursor to navigate through the queue. Each application's implied cursor is, however, independent of other application's cursors.
Regardless of the development platform, there is no limit to the number of applications that can use cursors to navigate through a queue.