Re: help bridging C and Ada

[Marc C <mc.provisional@gmail.com>]

On Monday, March 26, 2012 5:03:37 AM UTC-5, Brian Drummond wrote:

> This partly amounts to writing your own binding, as Simon suggested.
> The other part is to create a package with Ada procedures and functions 
> to interface to gstreamer, and use ONLY those functions everywhere else 
> in your code. Then only that package needs to interface to the C code.

My approach to writing bindings has gotten quite minimalist and application-specific in recent years.  Unless the project itself is developing the binding to a library, I create only the minimal subset of functions and data structures that the app actually needs to use.

I pay close attention to how the structs are being used by the C functions and which ones I actually need to read from and write to.  Between this and exploiting C's penchant for pointers, I can dramatically reduce the amount of binding code I need to write and verify.

If some struct, say, is passed as a function argument and its purpose is to hold some data being returned from the function, *but I don't care about any of that specific data*, then I just use a type that's derived from GNAT's Interfaces.C.Extensions package, like Opaque_Structure_Def_Ptr.  (This Extensions package is GNAT-supplied, but the types are nothing more than Addresses and access Addresses, so one can easily roll their own.)  Likewise, if a struct that I am binding to has some pointer fields that, again, I don't care about, I just use an Opaque_Structure_Def_Ptr-derived type.

Granted, if I or someone else needs a more thorough binding in the future, this binding would have to be extended.  But by not writing code that I don't know if I'll ever need, I save the time spent writing and debugging that, and spend it on making needed code now.

Marc A. Criley