Release 10.1A: OpenEdge Development:
Programming Interfaces

> ## Writing C functions

> Figure 18–4 shows the relationship between the `PRODSP()` dispatch routine that Progress supplies and your C functions.

> Figure 18–4: Relationship between PRODSP() and your C functions

> In general, your C functions can perform the following tasks:

> - Call HLC library functions to read data from and write data to Progress shared buffers and variables. HLC library functions are C functions that Progress provides to access the OpenEdge application environment from a user-written C function.

> - Perform operations using data from both OpenEdge and other sources. Other sources might include optical scanners, process monitor and control devices, spreadsheets, and other devices or applications not supported directly by OpenEdge.

> Your C functions consist of functions called directly from `PRODSP()` (top-level functions), and functions called directly or indirectly from the top-level functions (subfunctions). All top-level functions must return control to Progress, regardless of the subfunctions called.

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