[GRASS-dev] Re: [GRASS-user] Problems with v.outlier and v.lidar.edgedetection

[Glynn Clements]

Brad Douglas wrote:

> > > some minutes ago I have submitted a fix from Roberto Antolin
> > > to fix a v.outlier problem. It fixes a crash if qgis=name
> > > isn't used (so, maybe use that and it works)?
> > 
> > C question re that fix:   (vector/lidar/v.outlier/main.c)
> > 
> >     /* Structs' declarations */
> >     struct Map_info In, Out, Outlier, Qgis;
> >     struct Option *in_opt, *out_opt, *outlier_opt, *qgis_opt, *passoE_opt, *passoN_opt, \
> > 	*lambda_f_opt, *Thres_O_opt;
> > 
> > 
> > is the end of line "\" harmful or treated like whitespace?
> 
> It's interpreted as string literal concatenation.  In my experience,
> it's useful with strings:
> 
> Okay for gcc:
> fprintf(stderr, "blah blah"
>         "more blah blah");
> 
> More appropriate:
> fprintf(stderr, "blah blah" \
>         "more blah blah");
> 
> I'm sure Glynn has details, but that is my understanding.  I don't know
> if the same issues apply with variable declaration, but it isn't
> necessary at least with gcc.

The use of backslash-newline sequence is only useful in preprocessor
directives, which are terminated by any line break (LF on Unix, CRLF
on Windows, etc) which is not immediately preceded by a backslash.

In the above case, it's entirely unnecessary; a newline is treated no
differently to a space or tab in normal C code.

As for string concatenation: the preprocessor automatically
concatenates adjacent string literals, i.e. those which are separated
only by whitespace. E.g. the following are all equivalent:

	printf("hello world\n");

	printf("hello" " " "world" "\n");

	printf("hello "
		"world\n");

-- 
Glynn Clements <glynn at gclements.plus.com>