Re: cc1plus: note: source object is likely at address zero

On Thu, 5 Mar 2026, Jonny Grant wrote:

> Hello
>
> Is there a way to make these "notes" appear as warnings? That can then be upgraded to errors by -Werror
>
> https://godbolt.org/z/4ae71rfj8
>
> #include <string>
> #include <cstdio>
>
> typedef struct a
> {
>    int a;
>    int b;
>    char buf[10];
> } a_t;
>
> int main()
> {
>    a_t * i;
>    i = nullptr;
>    printf("%s\n", i->buf);
> }
>
> <source>: In function 'int main()':
> <source>:18:11: warning: 'int __builtin_puts(const char*)' reading 1 or more bytes from a region of size 0 [-Wstringop-overread]
>   18 |     printf("%s\n", i->buf);
>      |     ~~~~~~^~~~~~~~~~~~~~~~
> cc1plus: note: source object is likely at address zero
> ASM generation compiler returned: 0
> <source>: In function 'int main()':
> <source>:18:11: warning: 'int __builtin_puts(const char*)' reading 1 or more bytes from a region of size 0 [-Wstringop-overread]
>   18 |     printf("%s\n", i->buf);
>      |     ~~~~~~^~~~~~~~~~~~~~~~
> cc1plus: note: source object is likely at address zero
> Execution build compiler returned: 0
> Program returned: 139

That godbolt link uses options
 	-stdc=c++23 -O1 -Wall
but I get the same output with
 	-std=c++11 -Og -Wstringop-overread 
but with "-O0" or with no -O option at all the warning disappears.

-- 
Andrew C. Aitchison                      Kendal, UK
                    [email protected]