Hi Andrew!

On 11/13/22 23:12, Andrew Pinski wrote:
> 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

Great!  I'd like to implement it myself, as I've never written any GCC code yet, 
so it's interesting to me.  If you recall any (hopefully recent) case where a 
similar thing happened (the warning was already implemented and only needed a 
name), it might help me check how it was done.

BTW, I had another idea to add a suffix to string literals to make them 
unterminated:

char foo[3] = "foo"u;  // OK
char bar[4] = "bar";   // OK

char baz[4] = "baz"u;  // Warning: initializer is too short.
char etc[3] = "etc";   // Warning: unterminated string.

Is that doable?  Do you think it makes sense?

I have a code base that uses a mix of terminated and unterminated strings, and 
it would be nice to be able to tell the one I want in each case.

Cheers,

Alex

> 
>>
>> 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/>

-- 
<http://www.alejandro-colomar.es/>