[issue18225] ctypes Structure data size is incorrect

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc added the comment:

You can also use _pack_ = 1 to override the default alignment rules:
http://docs.python.org/3/library/ctypes.html#ctypes.Structure._pack_

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nosy: +amaury.forgeotdarc

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[issue18225] ctypes Structure data size is incorrect

[Tomer Levi]

New submission from Tomer Levi:

Whenever you create a ctypes.Structure with mixed ctypes, the size of all 
components is calculated by the size of largest one. This is especially 
irritating when trying to use Structure on bytearray.
The problem repeated for me in Python2.6 and 2.7 (both 32bit and 64bit 
versions) [My computer is 64bit]

Example:
#Creating a Structure that should take up 5 bytes
class Test(ctypes.Structure):
_fields_ = [(test, ctypes.c_byte),
(test2, ctypes.c_uint32),]

#Initiating the Structure
Test.from_buffer(bytearray(5))

--- OUTPUT 

Traceback (most recent call last):

  File ipython-input-45-cd4b7501baee, line 1, in module
Test.from_buffer(bytearray(5))

ValueError: Buffer size too small (5 instead of at least 8 bytes)

--
components: ctypes
messages: 191213
nosy: Tomer.Levi
priority: normal
severity: normal
status: open
title: ctypes Structure data size is incorrect
type: behavior
versions: Python 2.6, Python 2.7

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[issue18225] ctypes Structure data size is incorrect

[Alex Gaynor]

Alex Gaynor added the comment:

This is how padding works in the C ABI, not a bug.

--
nosy: +alex
resolution:  - invalid
status: open - closed

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