[Python-Dev] test_builtin failing? or just 64-bit platforms

Fredrik Lundh fredrik@pythonware.com
Sat, 1 Dec 2001 12:35:16 +0100

Barry A. Warsaw wrote:
>     TP> 20 bytes isn't enough to hold the result on a 64-bit box
>     TP> (insert rant about the idiot practice of trying to make stack
>     TP> buffers as small as possible).  You have 20 characters in your
>     TP> result, but need 21 to hold the trailing 0 byte too.  I don't
>     TP> know what snprintf does when there's not enough room, but I
>     TP> think you just showed us what it does on Tru64 <wink>.
> Heh, I was going to suggest that this might be a good place to
> substitute a call to PyString_FromFormat*() but then I read this
> little nugget:
> case 'd': case 'i': case 'x':
> (void) va_arg(count, int);
> /* 20 bytes should be enough to hold a 64-bit
>    integer */
> n += 20;
> break;

The size calculated by PyString_FromFormat is used to allocate a
Python string, not a C string.  The Python string allocator always
adds an extra 0 byte at the end.

(if it hadn't, I would have used 21 instead)