Mailing List Archive: [issue5145] struct.calcsize('cd') returns 16 instead of 9

[issue5145] struct.calcsize('cd') returns 16 instead of 9

Feb 3, 2009, 10:53 AM

Post #1 of 5 (337 views)

New submission from bob gailer <bgailer@gmail.com>:

struct.calcsize('cd') returns 16 instead of 9

struct.calcsize('dc') returns 9 as expected

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components: Extension Modules
messages: 81085
nosy: bgailer
severity: normal
status: open
title: struct.calcsize('cd') returns 16 instead of 9
type: behavior
versions: Python 2.5

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[issue5145] struct.calcsize('cd') returns 16 instead of 9 [ In reply to ]

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Feb 3, 2009, 11:13 AM

Post #2 of 5 (323 views)

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bob gailer <bgailer@gmail.com> added the comment:

Someone pointed out that one must consider alignment. I had overlooked
that. It makes sense that a d is double-word aligned.

Perhaps the documentation should mention alignment.

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[issue5145] struct.calcsize('cd') returns 16 instead of 9 [ In reply to ]

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Feb 3, 2009, 11:44 AM

Post #3 of 5 (325 views)

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Changes by Antoine Pitrou <pitrou@free.fr>:

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assignee: -> georg.brandl
components: +Documentation -Extension Modules
nosy: +georg.brandl

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[issue5145] struct.calcsize('cd') returns 16 instead of 9 [ In reply to ]

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Feb 5, 2009, 2:33 AM

Post #4 of 5 (319 views)

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Georg Brandl <georg@python.org> added the comment:

The docs have this sentence:

"""
By default, C numbers are represented in the machine's native format and
byte
order, and properly aligned by skipping pad bytes if necessary
(according to the
rules used by the C compiler).
"""

What would you suggest be added?

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[issue5145] struct.calcsize('cd') returns 16 instead of 9 [ In reply to ]

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Feb 5, 2009, 2:46 AM

Post #5 of 5 (319 views)

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STINNER Victor <victor.stinner@haypocalc.com> added the comment:

The default endiand and alignment is "native". Using <, >, = or !
endian, the alignement is standard.

Python 3.1a0 (py3k:69105M, Feb 3 2009, 15:04:35)
>>> struct.calcsize('cd')
12
>>> struct.calcsize('=cd')
9
>>> struct.calcsize('<cd')
9

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nosy: +haypo

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