About exitframe

A user exit is a subroutine invoked by a software package for a predefined event in the execution of the package. Clients of the package can substitute their own subroutines in place of the default ones provided by the package vendor to provide customized functionality.

A typical use is replacing the user exits provided by a sort/merge package, whereby the user program provides its own subroutines for comparing records. The procedures provided by the user take the place of the default routines (usually stubs that do nothing but return to their caller) provided by the package vendor.

Procedures provided as user exits are typically compiled into a static library and linked directly with the package to produce an executable program. Another approach employs dynamic libraries to accomplish the same thing.