Such as boost, where can I specify the following:
1.External c++ header file include path
2.External c++ source file
3.External c++ link library file path
Dirk's paper "Thirteen Simple Steps for Creating An R Package with an External C++ Library" gives an example src/Makevars:
CXX_STD = CXX11
PKG_CFLAGS = -I. -DGMP -DSKIP_MAIN
PKG_LIBS = $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS) -lgmpxx -lgmp
As you can see, additional libraries are specified in PKG_LIBS in this file. The src/Makevars approach assumes that you incorporate C++ code into your project using a standard package layout, as produced by Rcpp.package.skeleton(), with NAMESPACE and DESCRIPTION and so on.
According to Dirk's comments above, there is currently no way to specify an external library when C++ code is incorporated using the sourceCpp function, because that function provides an interface which is supposed to be multi-platform.