For example, on Visual Studio 2013 Update 2, we see the following (correct) warnings from cl.exe after adding a 64-bit configuration:

PulsecountEngine.cpp
....\src\engine\PulsecountEngine.cpp(233): warning C4267: 'initializing' : conversion from 'size_t' to 'const react::impl::uint', possible loss of data
SubtreeEngine.cpp
....\src\engine\SubtreeEngine.cpp(181): warning C4267: 'argument' : conversion from 'size_t' to 'int', possible loss of data

This is because ints are 4 bytes on cl.exe 64 -bit code, but size_t is 8 bytes.