Define EIGEN_CPLUSPLUS and replace most __cplusplus checks.

The macro `__cplusplus` is not defined correctly in MSVC unless building
with the the `/Zc:__cplusplus` flag. Instead, it defines `_MSVC_LANG` to the
specified c++ standard version number.

Here we introduce `EIGEN_CPLUSPLUS` which will contain the c++ version
number both for MSVC and otherwise.  This simplifies checks for supported
features.

Also replaced most instances of standard version checking via `__cplusplus`
with the existing `EIGEN_COMP_CXXVER` macro for better clarity.

Fixes: #2170

1 files changed, 1 insertions, 1 deletions

diff --git a/doc/examples/nullary_indexing.cpp b/doc/examples/nullary_indexing.cpp
index ca1745628..b74db5fd1 100644
--- a/doc/examples/nullary_indexing.cpp
+++ b/doc/examples/nullary_indexing.cpp
@@ -56,7 +56,7 @@ int main()
   B =  mat_indexing(A, ri+1, ci);
   std::cout << "A(ri+1,ci) =" << std::endl;
   std::cout << B << std::endl << std::endl;
-#if __cplusplus >= 201103L
+#if EIGEN_COMP_CXXVER >= 11
   B =  mat_indexing(A, ArrayXi::LinSpaced(13,0,12).unaryExpr([](int x){return x%4;}), ArrayXi::LinSpaced(4,0,3));
   std::cout << "A(ArrayXi::LinSpaced(13,0,12).unaryExpr([](int x){return x%4;}), ArrayXi::LinSpaced(4,0,3)) =" << std::endl;
   std::cout << B << std::endl << std::endl;