A function pointer is a data type whose values range over function addresses. Variables of this type appear in several programming languages such as C and Fortran. In Fortran, a dummy argument that appears in an EXTERNAL statement is a function pointer. Function pointers are supported in contexts such as the target of a call statement or an actual argument of such a statement.
A function pointer is a fullword quantity that is the address of a function descriptor. The function descriptor is a 3-word object. The first word contains the address of the entry point of the procedure, the second has the address of the TOC of the module in which the procedure is bound, and the third is the environment pointer for languages such as Pascal. There is only one function descriptor per entry point. It is bound into the same module as the function it identifies, if the function is external. The descriptor has an external name, which is the same as the function name, but without a leading . (dot). This descriptor name is used in all import and export operations.
Interlanguage Calling Conventions
Corresponding Data Types
Use the Subroutine Linkage Conventions in Interlanguage Calls
Sample Program: C Calling Fortran