Affected subclause: [cpp.predefined]
 Change: Whether 
__STDC__ is defined and if so, what its value is, are
implementation-defined
.   Rationale: C++ is not identical to ISO C
.  Mandating that 
__STDC__
be defined would require that translators make an incorrect claim
.Effect on original feature: Change to semantics of well-defined feature
.   Difficulty of converting: Semantic transformation
.   How widely used: Programs and headers that reference 
__STDC__ are
quite common
.