It does, after all, get defined in stddef.h AND c++config.h:

c++config.h:

namespace std
{
  typedef __SIZE_TYPE__     size_t;
  typedef __PTRDIFF_TYPE__  ptrdiff_t;

#ifdef __GXX_EXPERIMENTAL_CXX0X__
  typedef decltype(nullptr) nullptr_t;
#endif
}

stddef.h:

#define __SIZE_TYPE__ long unsigned int

So when a file does using namespace std, the Eclipse CDT code analysis gets confused and says the symbol is ambiguous. I don't know how gcc works around this, but does anybody have any suggestions on what to do for the eclipse code analysis?