[Python-Dev] Compiler warnings (original) (raw)

Scott Dial scott+python-dev at scottdial.com
Wed Feb 1 14:07:00 CET 2006

Thomas Wouters wrote:

My main problem with fixing the warnings is that I don't see the difference between, for example, the 'ssize' variable and the 'nchannels' variable

As was pointed out elsewhere, any variable that is passed by-reference to another function is ignored for the purposes of these warnings. The fact that the ioctl call with nchannels happens well after potential problem spots doesn't matter. It appears that GCC has eliminated it from the decision process for the purposes of these warnings already.

The problem roots from the ambiguity of the returns. At compile-time, there is no way for GCC that the return value will be negative in the error case, and thus the return may cause us to go down an execution path that ssize (and nchannels) need to be initialized. This check seems to be very shallow, even if you provide a guarantee that the return value will be well-behaved, GCC has already given up on figuring this out. The rule of thumb here seems to be "if you make a call to a function which provides the condition for the uninitialized variable is used, then the condition is decided to be ambiguous."

So, either the GCC people have not noticed this problem, or (more likely) have decided that this is acceptable, but clearly it will cause spurious warnings. Hey, after all, they are just warnings.

-- Scott Dial scott at scottdial.com dialsa at rose-hulman.edu

More information about the Python-Dev mailing list