Annex C (informative) Compatibility [diff]

C.3 C++ and ISO C++ 2011 [diff.cpp11]

C.3.1 [lex]: lexical conventions [diff.cpp11.lex]

[lex.ppnumber]
Change: pp-number can contain one or more single quotes.

Rationale: Necessary to enable single quotes as digit separators.

Effect on original feature: Valid C++ 2011 code may fail to compile or may change meaning in this International Standard.
For example, the following code is valid both in C++ 2011 and in this International Standard, but the macro invocation produces different outcomes because the single quotes delimit a character literal in C++ 2011, whereas they are digit separators in this International Standard:
#define M(x, ...) __VA_ARGS__
int x[2] = { M(1'2,3'4, 5) };
// int x[2] = { 5 };      — C++ 2011
// int x[2] = { 3'4, 5 }; — this International Standard