[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
.Each implementation must choose the behavior that will be most
useful to its marketplace
.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
.