qsort doesn't work for double arrays

[stephanepoirier]

BPO	16934
Nosy	@amauryfa, @mdickinson, @abalkin, @meadori
Files	testQSort33.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2013-01-11.14:57:43.131>
created_at = <Date 2013-01-11.14:13:56.837>
labels = ['ctypes', 'type-bug', 'invalid']
title = "qsort doesn't work for double arrays"
updated_at = <Date 2013-01-11.14:57:43.127>
user = 'https://bugs.python.org/stephanepoirier'

bugs.python.org fields:

activity = <Date 2013-01-11.14:57:43.127>
actor = 'mark.dickinson'
assignee = 'none'
closed = True
closed_date = <Date 2013-01-11.14:57:43.131>
closer = 'mark.dickinson'
components = ['ctypes']
creation = <Date 2013-01-11.14:13:56.837>
creator = 'stephane.poirier'
dependencies = []
files = ['28696']
hgrepos = []
issue_num = 16934
keywords = []
message_count = 3.0
messages = ['179680', '179683', '179685']
nosy_count = 5.0
nosy_names = ['amaury.forgeotdarc', 'mark.dickinson', 'belopolsky', 'meador.inge', 'stephane.poirier']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue16934'
versions = ['Python 2.6', 'Python 2.7', 'Python 3.3']

[stephanepoirier]

qsort doesn't sort arrays that are defined with double elements.
You can find attached a script that shows this function working well for int (as described in the ctypes documentation). If int array is replaced by double array qsort doesn't sort any more.
Even worse, with python 2.6, the difference between a[0] and b[0] may be nan.
The script can be launch by
python.exe testQSort33.py

[mdickinson]

What happens if you replace the line:

    CMPFUNC = CFUNCTYPE(c_double, POINTER(c_double), POINTER(c_double))

in your example code with

    CMPFUNC = CFUNCTYPE(c_int, POINTER(c_double), POINTER(c_double))

?

[mdickinson]

Closing as invalid: the issue is not in Python but with the CMPFUNC line. Your py_cmp_func should return an integer rather than a float to be compatible with libc.qsort.