R dyn.load("libcfile.so")

cfile.c

#include <R.h>
#include <Rinternals.h>
#include <Rdefines.h>
#include <stdio.h>

SEXP RIbdDbClose(SEXP handle)
	{	
	void *p = R_ExternalPtrAddr(handle);
	fprintf(stderr,"closing H5 file");
	if(p!=NULL)
		{
		FILE* f=(FILE*)p;
		fclose(f);
		}
	R_ClearExternalPtr(handle);
	return ScalarLogical(0);
	}

static void _RIbdDbFinalizer(SEXP handle)
	{
	RIbdDbClose(handle);
	}

SEXP RIbdDbOpen(SEXP Rfilename)
	{
	FILE* in;
	const char* filename= CHAR(STRING_ELT(Rfilename, 0));
	if(filename==NULL)  { fprintf(stderr,"Cannot open %s",filename); exit( -1);}

	in=fopen(filename,"r");
	if(in==NULL) { fprintf(stderr,"Cannot open %s",filename);  exit( -1);}
	SEXP ext = PROTECT(R_MakeExternalPtr(in, R_NilValue, R_NilValue));
	R_RegisterCFinalizerEx(ext,_RIbdDbFinalizer, TRUE);
    	UNPROTECT(1);
	return ext;
	}

cfile.R

dyn.load("libcfile.so")

Makefile

all: lib/libcfile.so
lib/libcfile.so: cfile.c
	mkdir -p lib
	R CMD SHLIB  -o $@ cfile.c

clean:
	rm -f *.o *.so lib/libcfile.so

OOREADME.md

compile

$ make clean && make
rm -f *.o *.so lib/libcfile.so
mkdir -p lib
R CMD SHLIB  -o lib/libcfile.so cfile.c
make[1]: Entering directory `/home/lindenb/src/tmp'
gcc -std=gnu99 -I/commun/data/packages/R-2.15-3/lib64/R/include -DNDEBUG  -I/usr/local/include    -fpic  -g -O2  -c cfile.c -o cfile.o
gcc -std=gnu99 -shared -L/usr/local/lib64 -o lib/libcfile.so cfile.o
make[1]: Leaving directory `/home/lindenb/src/tmp'

check LD_LIBRARY_PATH

$ echo $LD_LIBRARY_PATH
/home/lindenb/src/tmp/lib

execute R

$ R --vanilla  < cfile.R 

> dyn.load("libcfile.so")
Error in dyn.load("libcfile.so") : 
  unable to load shared object '/home/lindenb/src/tmp/libcfile.so':
  /home/lindenb/src/tmp/libcfile.so: cannot open shared object file: No such file or directory
Execution halted