Re: External data structures -- C400-L

Wondering if anyone would be able give a simple source example of an
external data structure definition in OPM C and ILE C ... if the concept
even exists.


Two ways that I know of #pragma mapinc and GENCSRC

They basically do the same thing, except that the #pragma is apreprocessor directive and therefore is run automatically when you invokethe compiler (making it more like RPG's version of this) and GENCSRC is aCL command that you run manually from the command line.

What these options do (both of them) is generate a source member thatcontains the external definition of the file. In both cases, you have to#include that source member in order to use the data structure definitionin your C program.


For example, if you put the following in your C source:

#pragma mapinc ("includeme","mylib/myfile(myrecfmt)","input","")
#include "includeme"

It will generate a (temporary) source member called "includeme" on thefly that contains the data structure definition. It will generate it usingthe record format called myrecfmt from the file mylib/myfile. It includesinput fields (i.e. fields that are not output only, like specifying *INPUTin RPG)

The next line includes that source member so that I can use it in myprogram. The name of the structure definition will beMYLIB_MYFILE_MYRECFMT_i_t (the "i" stands for input). So I can use thatstructure definition like that:


int main(int argc, char **argv) {

  MYLIB_MYFILE_MYRECFMT_i_t rec;

  memset(&rec.field1, ' ', 10);

  .
  .
}

That's probably not a great example, but hopefully you get the idea.

The only difference when using GENCSRC is that it's a CL command that yourun yourself (or put in a Makefile or whatever) that generates the sourcemember. You use that instead of the #pragma.

That way, you can see the source member that it generates, and keep itaround, etc. You still #include it the same way, and use it the same wayin your programs.

We're looking for examples in a C program that will cause a file or
external data structure to NOT be picked up by a DSPPGMREF.

I don't think those options will cause anything to be picked up byDSPPGMREF, since all they do is generate source members. The compilerdoesn't really know that the source came from a file -- it's just a datastructure definition. But, I haven't tested this. Give it a try and seewhat happens...