Calling R in BATCH mode from C programm
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.
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-- 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