The RFC API allows you to call ABAP function modules from C programs as well as receiving call requests issued from an ABAP program by the CALL FUNCTION interface.
The RFC API consists of three main parts:
the include file saprfc.h
This file contains data type and structure definitions as well as the prototypes (declarations) of the functions forming the API.
the include file sapitab.h
This file defines an interface for manipulating ABAP internal tables.
the library librfc.a (librfc32.dll, etc)
This library contains the functions of the API.