Maximillian Murphy
2008-Apr-29 16:19 UTC
[R] Calling R from C - part way there but need a push!
Dear All, I've read the manual on "Writing R Extensions" and in particular the part on calling R from C. (Most of the manual is about calling C from R, not the other way around.) The good news is that I can now call _some_ R from C, specifically the R functions which have C header files. However it isn't clear to me how to call R functions that are written in R. I imagine that there is a standard C function of the form Call_r_from_C("package name", "Rfunction name as a string", arg1, arg2, ...); where arg1 etc are standardised ways of representing R data structures in C. However I haven't been able to find such a function prototype in the R include/*.h files. See footnote (1). Can you point me in the right direction please? Is there a set of examples somewhere that I can peruse? Does R keep any state when being called from C? Should I think of it as being a co-process, so I can make consecutive calls to it and expect it to remember previous calls? I'm thinking of a sequence of calls such as "load library", "load R code from a file of my own", "set value of x", "make a call and read the values back into my C program"? Help is much appreciated. Regards, Max (1) The most likely include file is Rinterface.h and within that the most likely candidates seem to be: extern int (*ptr_R_ReadConsole)(const char *, unsigned char *, int, int); extern void (*ptr_R_WriteConsole)(const char *, int); extern void (*ptr_R_WriteConsoleEx)(const char *, int, int); but it turns out that they assume that R is running the terminal and these are requests to R to display or read from R's console. R isn't acting as the back end being given work and returning answers. (2) Googling "calling r from c" yields precisely five hits, most of which just point back at the R extensions document with vague "It's in there somewhere"'s. I've looked! (3) Leads suggested by help.search("C") Foreign(base): Foreign Function Interface Functions to make calls to compiled code that has been loaded into R. .Internal(base) Call an Internal Function '.Internal' performs a call to an internal code which is built in to the R interpreter. Only true R wizards should even consider using this function, and only R developers can add to the list of internal functions. (Definitely not me!) .Primitive(base) Call a "Primitive" Internal Function The advantage of '.Primitive' over '.Internal' functions is the potential efficiency of argument passing. (4) R code that I have called successfully is that with prototypes defined in e.g. include/R_ext/Applic.h
Duncan Murdoch
2008-Apr-29 17:29 UTC
[R] Calling R from C - part way there but need a push!
On 29/04/2008 12:19 PM, Maximillian Murphy wrote:> Dear All, > > > I've read the manual on "Writing R Extensions" and in particular the > part on calling R from C. (Most of the manual is about calling C > from R, not the other way around.) > > The good news is that I can now call _some_ R from C, specifically > the R functions which have C header files. However it isn't clear to > me how to call R functions that are written in R. I imagine that > there is a standard C function of the form > > Call_r_from_C("package name", "Rfunction name as a string", arg1, > arg2, ...);Not really. eval() is the main function to call from C. You construct an R expression, then evaluate it.> where arg1 etc are standardised ways of representing R data > structures in C. However I haven't been able to find such a function > prototype in the R include/*.h files. See footnote (1). Can you > point me in the right direction please? Is there a set of examples > somewhere that I can peruse?Section 5.10 (Evaluating R expressions from C) of the Writing R Extensions manual gives a couple of examples.> > > Does R keep any state when being called from C? Should I think of it > as being a co-process, so I can make consecutive calls to it and > expect it to remember previous calls? I'm thinking of a sequence of > calls such as "load library", "load R code from a file of my own", > "set value of x", "make a call and read the values back into my C > program"?The normal way to do it is to let R be in charge, and only occasionally call out to C: so then R keeps its state. What you are trying to do sounds more like writing a new front-end to R, which is much more involved: see Chapter 8 of that manual. Duncan Murdoch> > > Help is much appreciated. > > > Regards, Max > > > (1) The most likely include file is Rinterface.h and within that the > most likely candidates seem to be: > extern int (*ptr_R_ReadConsole)(const char *, unsigned char *, int, > int); > extern void (*ptr_R_WriteConsole)(const char *, int); > extern void (*ptr_R_WriteConsoleEx)(const char *, int, int); > > but it turns out that they assume that R is running the terminal and > these are requests to R to display or read from R's console. R isn't > acting as the back end being given work and returning answers. > > (2) Googling "calling r from c" yields precisely five hits, most of > which just point back at the R extensions document with vague "It's > in there somewhere"'s. I've looked! > > (3) Leads suggested by help.search("C") > Foreign(base): > Foreign Function Interface Functions to make calls to compiled > code that has been loaded into R. > > .Internal(base) Call an Internal Function > '.Internal' performs a call to an internal code which is built in > to the R interpreter. > > Only true R wizards should even consider using this function, and > only R developers can add to the list of internal functions. > > (Definitely not me!) > > .Primitive(base) Call a "Primitive" Internal Function > > The advantage of '.Primitive' over '.Internal' functions is the > potential efficiency of argument passing. > > (4) R code that I have called successfully is that with prototypes > defined in e.g. include/R_ext/Applic.h > > ______________________________________________ > R-help at r-project.org mailing list > stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.
Jeffrey Horner
2008-Apr-30 14:25 UTC
[R] Calling R from C - part way there but need a push!
Maximillian Murphy wrote on 04/29/2008 11:19 AM:> > Dear All, > > > I've read the manual on "Writing R Extensions" and in particular the > part on calling R from C. (Most of the manual is about calling C from > R, not the other way around.) > > The good news is that I can now call _some_ R from C, specifically the R > functions which have C header files. However it isn't clear to me how > to call R functions that are written in R. I imagine that there is a > standard C function of the form > > Call_r_from_C("package name", "Rfunction name as a string", arg1, arg2, > ...); > > where arg1 etc are standardised ways of representing R data structures > in C. However I haven't been able to find such a function prototype in > the R include/*.h files. See footnote (1). Can you point me in the > right direction please? Is there a set of examples somewhere that I can > peruse? > > > Does R keep any state when being called from C? Should I think of it as > being a co-process, so I can make consecutive calls to it and expect it > to remember previous calls? I'm thinking of a sequence of calls such as > "load library", "load R code from a file of my own", "set value of x", > "make a call and read the values back into my C program"? > > > Help is much appreciated.I would recommend studying the examples found in the tests/Embedding directory from the R sources. For instance, the following is from RNamedCall.c: /* Call the function foo() with 3 arguments, 2 of which are named. foo(pch="+", id = 123, c(T,F)) Note that PrintValue() of the expression seg-faults. We have to set the print name correctly. */ void bar1() { SEXP fun, pch; SEXP e; PROTECT(e = allocVector(LANGSXP, 4)); fun = findFun(install("foo"), R_GlobalEnv); if(fun == R_NilValue) { fprintf(stderr, "No definition for function foo. Source foo.R and save the session.\n"); UNPROTECT(1); exit(1); } SETCAR(e, fun); SETCADR(e, mkString("+")); SET_TAG(CDR(e), install("pch")); SETCADDR(e, ScalarInteger(123)); SET_TAG(CDR(CDR(e)), install("id")); pch = allocVector(LGLSXP, 2); LOGICAL(pch)[0] = TRUE; LOGICAL(pch)[1] = FALSE; SETCADDDR(e, pch); PrintValue(e); eval(e, R_GlobalEnv); SETCAR(e, install("foo")); PrintValue(e); R_tryEval(e, R_GlobalEnv, NULL); UNPROTECT(1); } Best, Jeff> > > Regards, Max > > > (1) The most likely include file is Rinterface.h and within that the > most likely candidates seem to be: > extern int (*ptr_R_ReadConsole)(const char *, unsigned char *, int, int); > extern void (*ptr_R_WriteConsole)(const char *, int); > extern void (*ptr_R_WriteConsoleEx)(const char *, int, int); > > but it turns out that they assume that R is running the terminal and > these are requests to R to display or read from R's console. R isn't > acting as the back end being given work and returning answers. > > (2) Googling "calling r from c" yields precisely five hits, most of > which just point back at the R extensions document with vague "It's in > there somewhere"'s. I've looked! > > (3) Leads suggested by help.search("C") > Foreign(base): > Foreign Function Interface Functions to make calls to compiled > code that has been loaded into R. > > .Internal(base) Call an Internal Function > '.Internal' performs a call to an internal code which is built in > to the R interpreter. > > Only true R wizards should even consider using this function, and > only R developers can add to the list of internal functions. > > (Definitely not me!) > > .Primitive(base) Call a "Primitive" Internal Function > > The advantage of '.Primitive' over '.Internal' functions is the > potential efficiency of argument passing. > > (4) R code that I have called successfully is that with prototypes > defined in e.g. include/R_ext/Applic.h > > ______________________________________________ > R-help at r-project.org mailing list > stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.-- biostat.mc.vanderbilt.edu/JeffreyHorner