Compiling Code Under C++11

The r11 R package provides an example of setting a package to use C++11 as the language specification.

Usage

To install the package, you must first have a compiler on your system that is compatible with R. For help on obtaining a compiler consult either macOS or Windows guides.

With a compiler in hand, one can then install the package from GitHub by:

# install.packages("devtools")
devtools::install_github("r-pkg-examples/rcpp-cpp11-usage")
library("r11")

Implementation Details

To compile code with C++11 or greater, you must specify the dependency in either the DESCRIPTION or Makevars{.win} files. For convenience, both are specified here. More details can be found in Writing R Extensions: 1.2.4 Using C++11 code. Furthermore, to test a C++-11 package on Travis-CI, you will need to change the default compiler. Details may be found after the jump.

DESCRIPTION

The DESCRIPTION file acts as a way to set the meta data for the R package. Using the SystemRequirements field and specifying C++11 will cause the package to default into using C++11. This is a popular option to take if the R package omits the Makevars/Makevars.win files.

SystemRequirements: C++11

Makevars

The Makevars file, as specified in Writing R Extensions: 1.2.1 Using Makevars, is a variant of Make that is unique to R. One custom variable that R defines is the CXX_STD. Specifying this alongside of a standard like CXX98, CXX11, CXX14, and so on will cause the appropriate language standard flag to be set.

CXX_STD = CXX11

Travis CI

To switch different compilers under the default Trusty image served by Travis-CI, you will need to use the PPA associated with the toolchain test builds. In addition, you will also have to set different configuration variables. Each step is broken down in the next portions. All steps are present in the .travis.yml file.

Within addons, we establish a connection to the toolchain test builds PPA and request the latest versions of gcc-8, gfortran-8, and g++-8.

addons:
  apt:
    sources: ['ubuntu-toolchain-r-test']
    packages:
      - gcc-8
      - g++-8
      - gfortran-8

We then set different environment configuration flags to use gcc-8, gfortran-8, and g++-8. In addition, we opt to use both cores available in the Travis CI container via the MAKEFLAGS statement.

env:
  global:
  - MAKEFLAGS="-j 2"
  - COMPILER=g++-8
  - CC=gcc-8
  - CXX=g++-8

Lastly, we setup environmental variables for R's Makevars file and specify compiler alternative with their respective priorities.

before_install:
  - mkdir -p ~/.R && touch ~/.R/Makevars
  - VER=-8
  - echo "CC=gcc$(VER)"        >> ~/.R/Makevars
  - echo "CXX=g++$(VER)"       >> ~/.R/Makevars
  - echo "CXX1X=g++$(VER)"     >> ~/.R/Makevars
  - echo "FC=gfortran$(VER)"   >> ~/.R/Makevars
  - echo "F77=gfortran$(VER)"  >> ~/.R/Makevars
  - sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-8 60 --slave /usr/bin/g++ g++ /usr/bin/g++-8
  - sudo update-alternatives --install /usr/bin/gfortran gfortran /usr/bin/gfortran-8 60

License

GPL (>= 2)