Functions that have C linkage and debug information can be used in a monitored expression. To do this, add the expression to the Monitors view using the Monitor Expression dialog box. This will add the function to the Monitors view and evaluate it, however it will be disabled and not updated as you debug. The monitor cannot be permanently enabled, however, you can evaluate it at any time by right-clicking the function and selecting Evaluate now.
For a list of function call limitations, see the related topic.