[R] Calling R in BATCH mode from C programm

[alkatz@post.tau.ac.il]

Dear, Prof. Repley,

thank you for the help,
of course, you are right. 

Redirection of stdin, stdout, stderr does the job.

If R script saves and reloads apprpriate workspaces,
then this method may be used instead of calling R functions from
C/C++ directly, wich is currently a problem, as I understand.

Here is C code that calls R in BATCH mode with arguments.
Then R runs script args.R wich reads the input arguments with Sys.getenv()
function and prints output to args.out and err.out files.

May be someone will find it usefull :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


char emsg[] = "can't redirect %s to %s\n";

void main ()
{
	int result, i;
	char buf[5120];

	if (!freopen( "args.R", "r", stdin )) {
		fprintf( stderr, emsg, "stdin", "args.R" );
		exit( 1 );
	}
	if (!freopen( "args.out", "w", stdout )) {
		fprintf( stderr, emsg, "stdout", "args.out" );
		exit( 1 );
	}
	if (!freopen( "err.out", "a", stderr )) {
		fprintf( stderr, emsg, "stderr", "err.out" );
		exit( 1 );
	}

	strcpy( buf, "Rterm --slave --no-save --no-restore ARG1=1 ARG2=2" );

	if (result = system( buf ))
		fprintf( stderr, "exit code = %d, errno = %d\n", result, 
errno );
}





Quoting Prof Brian Ripley <ripley at stats.ox.ac.uk>:

> >From C, that is not how you redirect stdin, stdout (and you have
> forgotten
> to redirect stderr).  I'll leave you to fathom that out (but as you are
> on
> Windows, the R sources should give you many useful clues).  (Note that
> you 
> do actually need a stdin and stdout to redirect, and a Windows
> application 
> does not necessarily have them set up.)
> 
> 
> On Tue, 20 May 2003 alkatz at post.tau.ac.il wrote:
> 
> > Hello R-people,
> > 
> > I have the following problem :
> > 
> > In order to run R script from DOS prompt in BATCH mode and pass it
> some
> > parameters I do the following :
> > 
> > 
> > Rterm --slave --no-save --no-restore <args.R> args.out ARG1=1 ARG2=2
> 
> That is actually <args.R >args.out: whether your form works depends on
> the 
> OS and shell.  The effect is to redirect stdin/stdout and is done either
> 
> by the shell or by the C initialization code.
> 
> 
> > It works fine :
> > the result is that the script args.R is isexecuted. Sys.getenv() sees
> the 
> > arguments ARG1 and ARG2, and the R creates output file args.out
> > 
> > 
> > Now I want to be able to call the same command from C application :
> > 
> > 
> > #include <conio.h>
> > #include <process.h>
> > #include <string.h>
> > 
> > 
> > void main()
> > {
> >    char *args[10], prog[80];
> >    int ch;
> > 
> >    strcpy(prog, "C:\\Program Files\\R\\RBase\\bin\\Rterm.exe "); 
> > 
> >    /* Arguments to Rterm.exe */
> >    args[0] = "--slave";
> >    args[1] = "--no-save";
> >    args[2] = "--no-restore";
> >    args[3] = "<args.R>";
> >    args[4] = "args.out";
> >    args[5] = "ARG1=1"; 
> >    args[6] = "ARG2=2";
> >    args[7] = NULL;
> >    
> > 
> >    _execl( prog, args[0], args[1], args[2], args[3], args[4], args[5],
> args[6], 
> > NULL);
> > }
> > 
> > 
> > Rterm starts, but writes to output :
> > 
> > ARGUMENT '<args.R>' __ignored__
> > ARGUMENT 'args.out' __ignored__
> > 
> > 
> > Command Sys.getenv("ARG1") returns correct result => R sees the rest
> of the 
> > arguments.
> > 
> > I tryed to type args[3] = "args.R" - without <> it does not help.
> > 
> > Does enyone know what might be my problem ??
> > 
> > Thanks,
> > Alex.
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> > 
> 
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>