Re: [whish] -Wunterminated-string-initialization: new warning

[Andrew Pinski <pinskia@gmail.com>]

On Sun, Nov 13, 2022 at 1:57 PM Alejandro Colomar via Gcc
<gcc@gcc.gnu.org> wrote:
>
> Hi!
>
> I'd like to get warnings if I write the following code:
>
> char foo[3] = "foo";

This should be easy to add as it is already part of the -Wc++-compat
option as for C++ it is invalid code.

<source>:2:19: warning: initializer-string for array of 'char' is too long
    2 | char     two[2] = "foo";   // 'f' 'o'
      |                   ^~~~~
<source>:3:19: warning: initializer-string for array of 'char' is too
long for C++ [-Wc++-compat]
    3 | char   three[3] = "foo";   // 'f' 'o' 'o'
      |                   ^~~~~


... (for your more complex case [though I needed to modify one of the
strings to exactly 8]

<source>:5:7: warning: initializer-string for array of 'char' is too
long for C++ [-Wc++-compat]
    5 |       "01234567",
      |       ^~~~~~~~~~

              else if (warn_cxx_compat
                       && compare_tree_int (TYPE_SIZE_UNIT (type), len) < 0)
                warning_at (init_loc, OPT_Wc___compat,
                            ("initializer-string for array of %qT "
                             "is too long for C++"), typ1);

That is the current code which does this warning even so it is just a
matter of adding an option to c-family/c.opt and then having
c++-compat enable it and using that new option here.

Thanks,
Andrew Pinski

>
> It's hard to keep track of sizes to make sure that the string literals always
> initialize to terminated strings.  It seems something that should be easy to
> implement in the compiler.
>
> A morecomplex case where it's harder to keep track of sizes is:
>
> static const char  log_levels[][8] = {
>      "alert",
>      "error",
>      "warn",
>      "notice",
>      "info",
>      "debug",
> };
>
> Here, 8 works now (and 7 too, but for aligmnent reasons I chose 8).  If tomorrow
> we add or change an entry, It'll be hard to keep it safe.  Such a warning would
> help a lot.
>
>
> An example program is:
>
> $ cat str.c
> char     two[2] = "foo";   // 'f' 'o'
> char   three[3] = "foo";   // 'f' 'o' 'o'
> char    four[4] = "foo";   // 'f' 'o' 'o' '\0'
> char    five[5] = "foo";   // 'f' 'o' 'o' '\0' '\0'
> char implicit[] = "foo";   // 'f' 'o' 'o' '\0'
>
> $ cc -Wall -Wextra str.c
> str.c:1:19: warning: initializer-string for array of ‘char’ is too long
>      1 | char     two[2] = "foo";   // 'f' 'o'
>        |                   ^~~~~
> /usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/Scrt1.o:
> in function `_start':
> (.text+0x17): undefined reference to `main'
> collect2: error: ld returned 1 exit status
>
>
> Here, I'd like that with the new warning, 'three' would also get warned.
>
> Cheers,
>
> Alex
> --
> <http://www.alejandro-colomar.es/>