Annex D (normative) Compatibility features [depr]

D.4 Comma operator in subscript expressions [depr.comma.subscript]

A comma expression ([expr.comma]) appearing as the expr-or-braced-init-list of a subscripting expression ([expr.sub]) is deprecated.
[Note 1:
A parenthesized comma expression is not deprecated.
— end note]
[Example 1: void f(int *a, int b, int c) { a[b,c]; // deprecated a[(b,c)]; // OK } — end example]