Introduction
When linking to a third party library it will often be necessary to explicitly specify a number of things:
-
#include
the header file in the C code - Use
PKG_CPPFLAGS
to nominate the search path for where the header file may be found (-I
flag) - Use
PKG_LIBS
to specify- Additional search paths for libraries (
-L
flag) - which libraries to link to (
-l
flag)
- Additional search paths for libraries (
Example: Linking to zlib
#include <R.h>
#include <Rinternals.h>
#include "zlib.h"
SEXP get_zlib_version(void) {
// const char * ZEXPORT zlibVersion(void);
return mkString(zlibVersion());
}
Click to show R code
code = r"(
#include <R.h>
#include <Rinternals.h>
#include "zlib.h"
SEXP get_zlib_version(void) {
// const char * ZEXPORT zlibVersion(void);
return mkString(zlibVersion());
}
)"
callme::compile(code)
# Compile the code with explicit link to library
compile(code, PKG_LIBS = "-lz")
# Call the function
get_zlib_version()
#> [1] "1.2.12"
Possible variations
# include a search path for the library
compile(code, PKG_LIBS = "-L/local/libs -lz")
# Include a search path for the header
compile(code, PKG_LIBS = "-lz", PKG_CPPFLAGS = "-I/usr/local/include")
# Link to a drop-in replacement
compile(code, PKG_LIBS = "-lzlibng")
# Use "pkg-config" to automatically determine appropriate flags
compile(code, PKG_LIBS = "`pkg-config --libs zlib`",
PKG_CPPFLAGS = "`pkg-config --cflags zlib`")