Dynamic Program

A  couple of weeks ago I  received some code snippets in reply to a problem I posted regarding dynamic program calls. Barbara Morris (thank you very much Barbara!) posted the original snippets.  I'm yet to get a clean-compile but I wanted to post my interpretation of the code and was wondering if somebody could confirm or correct my thoughts please? Following is Barbara's code with my annotations in italics:

#include <miptrnam.h>   include files for prototypes.miptrnam holds the prototype for rslvsp. I tried making sense of the header files but could not. I did this to find where _Program comes from in the rslvsp function .

#include <stdio.h>                                             

/*----------------------*/
/* typedef of a program */
/*----------------------*/
typedef void (somepgm_t)(int i, char *p);                               define the general form of the program that will eventually be called. I'm not sure what the

                                                                        correct terminology is, but I think this creates a template which the program eventually called has

has to map into?

#pragma linkage(somepgm_t, OS)                          defines a connection from somepgm_t     to the operating system. OS means OS400?

int main(void)                                                  the main function in my program.....
{
somepgm_t * somepgm = NULL;                             the pointer (*somepgm) is of type somepgm_t and is set to NULL which I presume is

a substitute value  or a C keyword for all zeroes? Somepgm will later on be set to the system space address of the program I want to call.

char pgmname[11] = "#JUNKLE";                           this is the program name. In my program I can just have a string variable and populate it

char libname[11] = "BMORRIS";                                   according to my own logic. I presume libname can be set to "*LIBL" ?

  /*----------------------------*/
  /* Get a system pointer to    */
  /* the program.               */
  /*----------------------------*/
somepgm = rslvsp (_Program, pgmname, libname,           obtain the system space address of where the program held in the pgmname field is.

_AUTH_OBJ_MGMT);                                I'm unsure where the _Program value comes from. Somepgm was declared earlier 

if (somepgm != NULL)                                            If the address is not null then the function found the program and obtained the address

  {
somepgm (5, "abcde");                                   therefore invoke it.  The 'form' of the call is as per the typedef earlier.

In my application I need to invoke a program which requires 3 parameters. Each parameter is in fact declared as an external DS via the #PRAGMA mapinc declaration. Do I therefore amend the typedef to look like ......typedef void(somepgm_t) (char *a, char *b, char *c)? where a,b, and c are the structure names assigned by the compiler?

I'm sorry for making this sound complicated, but I thought it might be useful for others approaching C for the first time and used to RPG constructs, especially in the way that external AS/400 objects are made visible to a program.

I've found a book called C For RPG Programmers but delivery is 4 weeks away.

Thank You.