Directing output to R.app GUI from compiled C code

On Mar 29, 2008, at 6:03 PM, Michael Braun wrote:

My C code is complex (and obscure), so I'd hate to bore the rest of  
the list with the details.  But perhaps this simple example will  
narrow things down. (My shared library is compiled using R CMD  
SHLIB, and loaded into R using dyn.load("xxx.so").  I call the  
function using the .C() function.  The application is straight  
numerical computation, with no fancy graphics or anything like that.)

If I print text using the R API function

	Rprintf("This is some text\n");

then I see that text, whether I run R from either the terminal or  
using R.app.  But, if I use, from the standard C library,

	printf("This is some text\n");

then I see it if I run R in the terminal window, but NOT in R.app.

A more complicated example is if I try to print a gsl vector

	gsl_vector_fprintf(stdout, X, "%.3f");

The result shows up in the terminal window, but not in R.app.  What  
I'd like to do is find something to replace stdout that would  
guarantee that the output goes to the appropriate R window.

I'm not doing anything special to flush output (I'm a new C  
programmer--is this something I need to do?).  I get this problem  
if I am trying to print a single line, as above, or a HUGE number  
of gsl_vectors (it was being caught in an infinite loop of printing  
vectors--and not seeing the output to let me know I was in the  
loop--that led me to this question).

I hope this is detailed enough.

Not really, because what you describe above works as designed:

#include <R.h>
#include <stdio.h>
void foo() {
  Rprintf("Friendly output\n");
  fprintf(stderr, "this goes to stderr\n");
  printf("Hello, world!\n");
}

dyn.load("foo.so")
.C("foo")

Friendly output
list()
this goes to stderr
Hello, world!

As you can see the stdout output is in gray, stderr is in red and  
regular console output is in black (if you use default colors). All  
is there. (Note, however, the output order is not necessary linear,  
because stdout/err must be captured asynchronously).

Please let me know if more information is needed.

Which version of R and R.app are you using? Also the output can be  
disabled in the preferences - if you did so, it won't appear. Can  
you see the output of "system('ls')"?

Cheers,
S

[This message also contains rich version of the e-mail to illustrate  
the point. Apologies to plain text recipients.]

On Mar 29, 2008, at 5:24 PM, Simon Urbanek wrote:

Michael,

On Mar 29, 2008, at 2:23 PM, Michael Braun wrote:

I am a recent convert from Linux to Mac (OS X 10.5.2 on a Mac  
Pro), and  am trying to direct some output from  compiled C code  
to the R.app GUI.  For simple things, of course, I use Rprintf  
from the R API.  But there are other cases (e.g., using the  
matrix print routines in GSL) for which Rprintf is  
inappropriate.  When I was in Linux-land, I could direct the  
output to stdout with no problem (and I can still do that running  
R from a terminal window on OS X).  But if I run my app under  
R.app, the output never makes it to the screen (naturally,  
because R.app is not standard output).

If we are to assist you, you should tell us more about your  
application (the C code), because R.app *does* print stdout and  
stderr (just try running system("ls")). Your application is very  
likely doing something to prevent the output from being processed  
(not flushing the output, printing unterminated lines, not  
allowing R to process events...).

Cheers,
Simon

So, is there an output file that I can use in place of stdout that
will get my output to the R.app GUI (and preferably, to a terminal
window session as well)?

Thanks!

Michael




Michael Braun
Assistant Professor of Management Science (Marketing Group)
MIT Sloan School of Management
One Amherst St., E40-169
Cambridge, MA 02142
braunm at mit.edu
617-253-3436

Michael Braun
Assistant Professor of Management Science (Marketing Group)
MIT Sloan School of Management
One Amherst St., E40-169
Cambridge, MA 02142
braunm at mit.edu
617-253-3436