The following diagram shows the interaction of the SAP Automation GUI Library with R/3 and with your application, for applications written in C.

When an R/3 end-user access R/3 screens, SAPGUI interacts between the user and the R/3 application server.

The GUI Library allows your C program to access the data stream that is sent between the R/3 application server and its SAPGUI process and use this data in your program. The GUI Library component interacts with the R/3 SAPGUI and the R/3 application server, placing the screen data that is communicated between them in a special data structure. Your C program can then read or write data into or out of that data structure.

A C program using the GUI Library can use the interaction between an end user and SAPGUI screens, or it can replace the GUI screens with its own interface, while blocking the SAPGUI screens from being displayed.