Re: wcstok(3) code sample

["Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>]

Hi Stefan,

On 7/12/21 11:07 AM, Stefan Kanthak wrote:
> Hi,
> 
> the examples section of wcstok(3) shows the following code
> which exhibits undefined behaviour and typically segfaults:
> 
> <https://man7.org/linux/man-pages/man3/wcstok.3.html#EXAMPLES>
> 
> |  wchar_t *wcs = ...;
> |  wchar_t *token;
> |  wchar_t *state;
> |  for (token = wcstok(wcs, " \t\n", &state);
> |       token != NULL;
> |       token = wcstok(NULL, " \t\n", &state)) {
> |       ...
> |  }
> 
> The string literal pointed to by wcs is read-only, and an
> attempt to modify a string literal results in undefined
> behaviour; wcstok() but writes NULs into its input string.
> 
> FIX: replace the first line with either
> 
> |  wchar_t *wcs = strdup(...);
> 
>       or
> 
> |  wchar_t wcs[] = ...;

That code is a bit unfortunate.  It is not a complete program, so it can 
be interpreted in different ways, one of them the one you said, which 
results in UB.

I guess the intent of the code was that wcs was assigned a pointer to a 
wchar_t * (not a literal), and therefore, it would be correct.  The code 
predates version control, so we'll never know...

Would you mind sending a complete example?

Thanks,

Alex

> 
> regards
> Stefan
> 


-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/