[GRASSLIST:4545] Re: Advice on changing source code for g.region command

[Glynn Clements]

Roy Sanderson wrote:

> The observant amongst you will spot that east and west have swapped round.
> As my colleagues have the g.region command liberally embedded in various
> scripts, and the output is read by their own C programs, this is causing
> problems.  My suggestion to them that they should go through all their C
> programs and edit the input lines was not well received!
> 
> As an alternative, I'm wondering whether to alter the Grass 5.0 code
> myself, and recompile it.  I've not done this before, but assume the
> offending lines are in
> /src/grass5.0.0pre5/src/general/g.region/cmd/printwindow.c  Am I safe in
> simply swapping the fprintf lines round for east and west so that they
> match the Grass4.3 format, and re-compiling?

Probably.

IOW, it's unlikely that anything in GRASS relies upon the format;
however, I'm not about to perform exhaustive analysis, and I doubt
that anyone else is either.

To elaborate slightly:

It's safe to assume that nothing which is written in C will attempt to
parse the output from "g.region -p", as it's vastly simpler to just
use G_get_window() directly.

Some scripts may parse the output from "g.region -p", but the only one
which I've found (3d.view.sh) looks for the strings "north", "south"
etc rather than relying upon the order.

One final point: while the change in question is probably accidental
(and unnecessary), the output format of GRASS programs should not be
considered a defined interface, and may change in future versions.

While such changes are unlikely to be made gratuitously, backward
compatibility isn't the only consideration. E.g. it's entirely
conceivable that the output from future versions of g.region may
include additional information.

-- 
Glynn Clements <glynn.clements at virgin.net>