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A general description is here.
There is some support for compiling C++11 code in packages. The file ‘src/Makevars’ or ‘src/Makevars.win’ should define the macro ‘USE_CXX1X’ (with an empty value). Where needed, an alternative compiler can be specified by setting macros ‘CXX1X’, ‘CXX1XFLAGS’ and so on, either when R is configured or in a personal/site ‘Makevars’ file. (The default is to use ‘$(CXX) -std=c++11’ except on Windows where ‘-std=c++0x’ is used, as supported by ‘g++ 4.6.x’.)
Other standards supported by the compiler can be specified by e.g. ‘USE_CXX1X = -std=c++1y’ .