[Bug c/116443] New: String values not accepted for case labels

[Bug c/116443] New: String values not accepted for case labels

[rasmus.tempcache at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116443

            Bug ID: 116443
           Summary: String values not accepted for case labels
           Product: gcc
           Version: 14.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rasmus.tempcache at gmail dot com
  Target Milestone: ---

String character values do not seem to be able to be evaluated in switch cases.
This gives the error "case label does not reduce to an integer constant".

Here's an example that works in clang but not in GCC:

static int function(int var)
{
  switch (var)
  {
  case "str a"[0] + "str b"[2]:
    return 0;

  default:
    return 1;
  }
}

I'm currently using 14.1.0 and have been following for the changelogs for newer
releases but haven't noticed this mentioned in any of them.

[Bug c/116443] String values not accepted for case labels

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116443

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I don't think this is technically a bug. The C standard requires an integral
constant expression for a case label, and "str"[0] is not required to be an
integral constant expression. The C standard does allow implementations to be
flexible in what they consider to be integral constant expressions, so Clang is
allowed to accept this code, but it's not required to accept it.

So if GCC accepted this, it would be as a non-standard extension.

[Bug c/116443] String values not accepted for case labels

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116443

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Slight correction, the correct term is "integer constant expression", and C
requires a "constant expression" for a case label, not an integer constant
expression.

But the rest still stands, GCC is not required to accept this, but Clang is
allowed to accept it, see C17 6.6 "An implementation may accept other forms of
constant expressions."

[Bug c/116443] String values not accepted for case labels

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116443

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup.

*** This bug has been marked as a duplicate of bug 89408 ***