8 Apr
2012
8 Apr
'12
7:43 p.m.
On 04/08/2012 12:01 PM, Egor Sanin wrote:
Because it's valid to do this according to the docs:
http://jackaudio.org/files/docs/html/group__TransportControl.html#ga5f08eb7…
If pos is NULL it just ignores it. It's not an error at all.
OTOH, if pos is uninitialized, then jack will try to write the data to
whatever random address in in pos... and that will usually segfault.
In B, pos
(IIRC) would be initialized to NULL as it is in the file scope.
So when you call jack_transport_query, you have provided a pointer to
NULL, where any memory access will be invalid.
But then why does jack_transport_query not give any error when it is
passed a NULL pointer in the form of pos? If I remove the line
frame = pos->frame;
from B, the code runs, state is set properly and jackd doesn't report problems.
This suggests that pos is indeed NULL, and you tried to dereference a
null pointer... which will always segfault.
-gabriel