swprintf - terminating null in case n < input length

[Petr Muller <pmuller at redhat dot com>]

Hi, 

I'm curious about the behavior of swprintf function in the case n is
lower than input length. POSIX says that the 'terminating zero shall be
always added' and (in 'return code') 'if n or more characters were
requested to write, swprintf should return -1'. glibc's swprintf seems
to not add the zero in this case, so for

wchar_t input[7]   = L"6chars\0"
wchar_t buffer[10] = L"---------\0"

swprintf(buffer, 5, L"%ls", input);

you will get buffer = "6cha-----\0", which is 4 characters copied and
missing null. -1 returned.

Is this behavior a bug, or is it intentional (aka: n < input length is
an error, thus the side effect on the buffers is not defined)?

I've already traced this to the source and can provide a patch, but I'm
not sure if that behavior is really a bug.

Petr

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