Re: Bug in Newlib's snprintf implementation

[Corinna Vinschen <vinschen at redhat dot com>]

On Feb 23 05:12, Jeffrey Walton wrote:
> On Fri, Feb 23, 2018 at 4:43 AM, Corinna Vinschen <vinschen@redhat.com> wrote:
> > Slight correction: snprintf returns the size of the string it would
> > have produced if it hadn't truncated the output.  So a size value
> > of 4 ("test" would have been the desired result) is correct.
> 
> I don't believe this is correct. The string of 'test' and the NULL
> requires 5, not 4. 4 indicates truncation.

4 is correct:

> According to the man page (https://linux.die.net/man/3/snprintf):
> 
> <SNIP>
> RETURN VALUE
> 
> Upon successful return, these functions return the number of
> characters printed (excluding the null byte used to end output to
> strings).
> 
> The functions snprintf() and vsnprintf() do not write more than size
> bytes (including the terminating null byte ('\0')). If the output was
> truncated due to this limit then the return value is the number of
> characters (excluding the terminating null byte) which would have been
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> written to the final string if enough space had been available. Thus,
> a return value of size or more means that the output was truncated.
> (See also below under NOTES.)
> </SNIP>

The desired result is a string with 4 chars, "test".  The return value
reflects the desired result, *excluding* the NUL, if the truncation
wouldn;t have been necessary.  That's 4.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

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