Re: [Tinycc-devel] _Generic or __builtin_choose_expr

[Michael Matz]

Hi,

On Tue, 4 Jul 2017, Michael Matz wrote:

> Ugh, you're right.  Indeed the standard doesn't mandate a const char[] 
> type for string literals (I was confused because it does say that 
> modification of string literals is undefined, i.e. that's an extension).  
> Let me work on this a bit.

Actually, not much need for work.  I've checked GCC sources and, even 
though it wonders in a comment if it's a good idea to change expression 
types with warning flags, it indeed does so; so if for nothing else than 
compatibility I've reverted the patch.

The hack in the current patch for _Generic (to regard string literals as 
const char* always) isn't needed.  GCC indeed differs in behaviour 
depending on the warning flag, also in _Generic:

-----------------------
extern int printf(const char *,...);
int main()
{
  const char *msg;
  msg = _Generic("foo", const char *:"const char*", char*:"char *", 
default:"something else");
  printf ("type \"foo\" = %s\n", msg);
  return 0;
}
-----------------------
% gcc-6 -Wwrite-strings x.c && ./a.out
type "foo" = const char*
% gcc-6 -Wno-write-strings x.c && ./a.out
type "foo" = char*

So, thanks for checking after me ;)


Ciao,
Michael.