| msg172616 - (view) |
Author: Brian Thorne (Thorney) |
Date: 2012-10-11 02:42 |
| The Python docs for ctypes have embedded examples including: >>> c_int() c_long(0) But on my machine I get the (more expected?): >>> c_int() c_int(0) Perhaps if some machines expect otherwise that should be documented, otherwise might we change them. |
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| msg172624 - (view) |
Author: Chris Jerdonek (chris.jerdonek) *  |
Date: 2012-10-11 07:21 |
| > Perhaps if some machines expect otherwise that should be documented, otherwise might we change them. The very beginning of the ctypes documentation has documentation to that effect: "Note: Some code samples reference the ctypes c_int type. This type is an alias for the c_long type on 32-bit systems. So, you should not be confused if c_long is printed if you would expect c_int — they are actually the same type." http://docs.python.org/dev/library/ctypes.html#ctypes-tutorial Does that address your suggestion? |
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| msg172625 - (view) |
Author: Brian Thorne (Thorney) |
Date: 2012-10-11 07:36 |
| > The very beginning of the ctypes documentation has documentation to that effect >Does that address your suggestion? Thanks Chris, that explains why the difference is present on non 32 bit platforms. Would using c_long for the examples produce the expected output on 64 and 32 bit systems? Just an idea to try remove potential confusion. |
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| msg172626 - (view) |
Author: Chris Jerdonek (chris.jerdonek) * |
Date: 2012-10-11 07:51 |
| I don't know off-hand. But maybe an additional note or code comment at the first instance in a code example would help. Switching the examples to c_long might serve only to shift potential confusion from the examples to someone's personal machine. |
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| msg172735 - (view) |
Author: Ezio Melotti (ezio.melotti) * |
Date: 2012-10-12 09:41 |
| The note at the beginning could be turned in an actual note using the `.. note:` markup. This will make it more visible. |
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| msg233751 - (view) |
Author: Eryk Sun (eryksun) *  |
Date: 2015-01-09 13:08 |
| It's not correct that "[The c_int] type is an alias for the c_long type on 32-bit systems". Actually it's an alias if int and long are the same size. Here's the relevant snippet from __init__: if _calcsize("i") == _calcsize("l"): # if int and long have the same size, make c_int an alias for c_long c_int = c_long c_uint = c_ulong else: class c_int(_SimpleCData): _type_ = "i" _check_size(c_int) class c_uint(_SimpleCData): _type_ = "I" _check_size(c_uint) Notably, int and long are the same size on 64-bit Windows: >>> sizeof(c_void_p) # 64-bit 8 >>> c_int <class 'ctypes.c_long'> >>> sizeof(c_long) 4 |
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| msg233765 - (view) |
Author: Berker Peksag (berker.peksag) * |
Date: 2015-01-09 16:42 |
| > It's not correct that "[The c_int] type is an alias for the c_long type on 32-bit systems". Actually it's an alias if int and long are the same size. It's already documented at https://docs.python.org/dev/library/ctypes.html#ctypes.c_int "On platforms where sizeof(int) == sizeof(long) it is an alias to c_long." Do you want to write a patch to update the original note? |
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| msg266922 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2016-06-02 19:08 |
| New changeset 1775abf47061 by Berker Peksag in branch '3.5': Issue #16192: Clarify when c_int is an alias to c_long in ctypes documentation https://hg.python.org/cpython/rev/1775abf47061 New changeset 9954e29b8678 by Berker Peksag in branch 'default': Issue #16192: Merge from 3.5 https://hg.python.org/cpython/rev/9954e29b8678 |
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| msg266965 - (view) |
Author: Eryk Sun (eryksun) * |
Date: 2016-06-02 21:55 |
| > ``sizeof(long double) == sizeof(double)`` it is an alias to > :class:`c_double`. This should be "``sizeof(long) == sizeof(int)`` ... :class:`c_long`". |
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| msg266975 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2016-06-02 22:18 |
| New changeset dfde53cf07e6 by Berker Peksag in branch '3.5': Issue #16192: Fix copy and paste mistake noticed by Eryk Sun https://hg.python.org/cpython/rev/dfde53cf07e6 New changeset 7f3ebd86464b by Berker Peksag in branch 'default': Issue #16192: Merge from 3.5 https://hg.python.org/cpython/rev/7f3ebd86464b |
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