Underscores work well as a digit separator for C++03 [N0259] [N2281]. But with C++11, there exists a potential ambiguity with user-defined literals [N2747]. While the likely resolution will be some form of "max munch" rule, some mechanism must be present to disambiguate when max munch is too much.
[^] # Re: Séparateur de chiffre
Posté par zul . En réponse au journal C++14. Évalué à 3.
D'après N3499, http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3499.html