What's special about R and L in the C++ preprocessor?

Question

I ran the following code through the Visual Studio 2013 preprocessor. The output surprises me.

Contents of hello.cpp:

#define A(j) #j

A(A?)
A(B?)
A(         


        

Answer 1

This appears to be a bug in the MSVC preprocessor. The good news is that depending on how picky you are with your output, you can work around the issue by putting a space after the R or L.

A(L ?p:q), // "L ?p:q"