Re: 2.6 - 3.x bytearray from c_char_p

It looks like you have solved your problem.  I am not sure if you still have questions.

You can create a Unicode string with
u = u'hello'
and then check the type
>>>type(u) 
<type 'unicode'>

As opposed to
s = 'hello'
>>>type(s)
<type 'str'>

A POINTER(c_char) will represent an array of 1 byte character values.
I just realized a better solution.
A POINTER(c_byte) will represent an array of 1 byte integers.  
This will then get you what you want without needing to use "map(ord, )" or struct.unpack.


If the description of map() was too confusing, here are some examples:
def sqrt(x):
    return x*x

>>>map(sqrt, [1,2,3,4])
[1, 4, 9, 16]

def add(x,y):
    return x + y

>>>map(add, [1,2,3], [4,5,6])
[5, 7, 9]

ie. [1+4, 2+5, 3+6]

You can also do list comprehensions
>>>[sqrt(x) for x in [1,2,3,4]]
[1, 4, 9, 16]
>>>[add(x,y) for (x,y) in zip([1,2,3],[4,5,6])]
[5, 7, 9]

--Jeff 


-----Original Message-----
From: Thomas Stover [mailto:[email protected]] 
Sent: Tuesday, May 17, 2011 4:06 PM
To: [email protected]
Subject: Re: [ctypes-users]2.6 - 3.x bytearray from c_char_p

Turns out it actually wasn't working. It stopped on bytes of value 0
thinking it was a NULL termination.

I found in the docs:

class ctypes.c_char_p¶
    Represents the C char * datatype when it points to a zero-terminated
string. For a general character pointer that may also point to binary data,
POINTER(c_char) must be used. The constructor accepts an integer address,
or a string.


So the callback argument is of type POINTER(c_char) instead of c_char_p.

Given a parameter, Pointer, of such a type, to get a usable string of
"Length" size, use the notation Jeff gave:

def Callback(Pointer, Length):
    Usable = Pointer[:Length]

-- 
www.thomasstover.com
FLYNN LIVES!

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