HLC and OpenEdge
The Host Language Call (HLC) Interface is an OpenEdgeŽ feature that allows you to write and call your own C language functions directly from a Progress procedure using the 4GL CALL statement. Using HLC library functions, your C functions can read from or write to shared variables and shared buffer fields defined in the Progress context, interact with the Progress display, test for Progress interrupts, and access Progress-managed timer services. Ultimately, you can use HLC to access devices not supported directly in Progress (such as process sensors or ATM terminals), and exchange data between your Progress procedures and these devices.
HLC provides access to third-party application program interfaces from your 4GL applications, similar to using shared libraries in the Windows environment (see the chapter on shared library and DLL support in OpenEdge Development: Programming Interfaces ).
Figure 18–1 shows a top-down structure diagram for an OpenEdge application that calls your application functions using HLC.
