Yes, the differences between C++14 and 98 are night-and-day different. Quite a few important language features, and plenty of new libraries (including threading and lambdas).
There aren't any (AFAIK) explicit breaks of '98 code in '14. So the theory is that code should compile with the new compiler fine, but you'll likely hit some issues.
Check out Scott Meyers book: Effective Modern C++ for the deltas.
There are definitely backwards-incompatible changes in the things that were added since C++98. For one, there's a whole set of new keywords that's going to break any code that used them as identifiers.
Then there's a keyword that was re-purposed to do something totally different: in C++, auto used to be a storage duration specifier. In C++11 it is used to indicate type inference.
There were also changes that, while not breaking source compatibility, basically required implementations to break binary compatibility going from C++98 to C++11. This in particular resulted in a gigantic mess.
With regard to breaking changes the C++ committee is not anywhere near as conservative as the one for C.
There is one break that I know of. `>>` is now parsed as two tokens, and will preferentially mean "close two templates" instead of "right bit shift" in cases of ambiguity.
There aren't any (AFAIK) explicit breaks of '98 code in '14. So the theory is that code should compile with the new compiler fine, but you'll likely hit some issues.
Check out Scott Meyers book: Effective Modern C++ for the deltas.