Nathaniel Hayes wrote:
I am working on creating a python API for a dll for a daqboard we have
here. I have the documentation for the library, as well as the C,
Delphi and VB api. I have decided to use ctypes for the project, and
most is working out alright. However I have run in to considerable
headaches when dealing with pointers to arrays. The function I am first
working with, requires a pointer to an array of strings that will
contain the names of all the devices installed. Here is a snippet of
the code I have so far:
def GetDeviceList():
"""Returns a list of currently configured device names"""
devices = []
count = GetDeviceCount()
countpnt = ct.pointer(ct.c_int(count))
devlist = (ct.c_char_p * count)()
daq.daqGetDeviceList(devlist, countpnt)
for i in devlist:
devices.append(i)
return devices
Using Python 2.6.3 the IDLE goes into an infinite loop of, from what I
can gather, Tkinter errors, and Im unable to kill the command to
actually read all of the errors.
When using Python 3.1.1, I get this error:
Python 3.1.1 (r311:74483, Aug 17 2009, 17:02:12) [MSC v.1500 32 bit
(Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> import daqX
>>> daqX.GetDeviceList()
Traceback (most recent call last):
File "<pyshell#1>", line 1, in <module>
daqX.GetDeviceList()
File "C:\Python31\daqX.py", line 54, in GetDeviceList
for i in devlist:
ValueError: invalid string pointer 0x42716144
>>>
The digits in that pointer value look suspiciously like the character
codes of a string rather than an actual address:
>>> "\x42\x71\x61\x44"
'BqaD'
It looks like the first 4 characters of a string starting 'DaqB' are
being used as a string pointer on a little-endian platform.
I am really at a loss here, so any insight at all would be great.
Something odd though, is that when I pass just c_char_p instead of an
array of c_char_p, I receive the one device I have installed on this
computer, and it works great. However, when I make an array of just one
item, I get these odd errors.
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