Hi list,
I'm currently writing python code that writes a small binary file to be used by
another device which code is written in C.
The python code runs on a little endian CPU, and unfortunately, the other
device is using a big endian MIPS.
My problem is the following: I cannot make an array of n int work in big
endian, I can workaround the problem by creating n intergers, which is nicely
done thanks to list comprehension but that seems to me like a misuse of the
ctypes modules.
ctypes is expecting a 'c_uint_be_Array_5' (note the _be_ for big endian), and I
don't know how to construct such object.
I hope I am clear.
Thanks,
JM
here's a code sample (python 2.7):
--------------------
import ctypes, sys
iarray = ctypes.c_uint32*5 # array of 5 unsigned 32 bits
class Foo(ctypes.Structure):
"""Native byte order, won't work on my big endian device"""
_fields_ = [('bar', iarray)]
class Foo_be(ctypes.BigEndianStructure):
"""big endian version, but python code fails"""
_fields_ = [('bar', iarray)]
class Foo_be_working(ctypes.BigEndianStructure):
"""Working big endian version, looks more like a workaround."""
_fields_ = [('bar%i'%i, ctypes.c_uint32) for i in range(5)]
print sys.version
f = Foo(iarray(0,1,2,3,4))
print "uint32 array: ", f.bar
f_be = Foo_be_working(0,1,2,3,4)
print "bar0 and bar5: ", f_be.bar0, f_be.bar5
f_be = Foo_be(iarray(0,1,2,3,4)) # will raise an exception
--------------------
The output
2.7.3 (default, Mar 13 2014, 11:03:55)
[GCC 4.7.2]
uint32 array: <__main__.c_uint_Array_5 object at 0x1cf4560>
bar0 and bar4: 0 4
TypeError: incompatible types, c_uint_Array_5 instance instead of
c_uint_be_Array_5 instance
24
---> 25 f_be = Foo_be(iarray(0,1,2,3,4))
26
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