# User Interface Library

This section describes the functions in the User Interface Library. The User Interface Library is a set of functions for controlling a graphical user interface. A graphical user interface is a collection of objects such as menu bars, panels, controls, and graphs. You can construct the user interface programmatically or with the User Interface Editor. To access information about each function, you can use the function tree list of User Interface Library functions or click on the function name in the left pane of the Help window, in the Alphabetical List of Functions section of the Contents tab.

## Reporting Errors

All the functions in the User Interface Library return an integer code containing the result of the call. If the return code is negative, an error occurred. Otherwise, the function completed successfully. Refer to the User Interface Library error messages section for a complete list of error messages. You can also use GetUILErrorString to convert the error number returned into a text error message.