ctypes: problem with large integers

[abalkin]

BPO	1703952
Nosy	@theller, @abalkin

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/theller'
closed_at = <Date 2007-07-13.17:51:28.000>
created_at = <Date 2007-04-19.21:51:13.000>
labels = ['extension-modules']
title = 'ctypes: problem with large integers'
updated_at = <Date 2007-07-13.17:51:28.000>
user = 'https://github.com/abalkin'

bugs.python.org fields:

activity = <Date 2007-07-13.17:51:28.000>
actor = 'theller'
assignee = 'theller'
closed = True
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2007-04-19.21:51:13.000>
creator = 'belopolsky'
dependencies = []
files = []
hgrepos = []
issue_num = 1703952
keywords = []
message_count = 4.0
messages = ['31837', '31838', '31839', '31840']
nosy_count = 2.0
nosy_names = ['theller', 'belopolsky']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1703952'
versions = ['Python 2.5']

[abalkin]

Python 2.5 (r25:51908, Nov 24 2006, 11:03:50)
[GCC 3.4.4 20050721 (Red Hat 3.4.4-2)] on linux2
>>> from ctypes import *
>>> c_int(2**31).value
-2147483648
>>> c_long(2**32-1).value
-1

In a 64-bit build, the situation is even worse:

>>> c_int(int(2**32)).value
0
>>> c_int(2**32).value
0

Another way to see the problem:
>>> c = CDLL(None)
>>> c.printf("%d\n", 2**32)
0
2

[theller]

This works as designed. ctypes intentionally does no overflow checking when using the c_int, c_uint, and related integer types. Instead, only the available bits are used - just as in C.

Closing as invalid (sorry).

[abalkin]

An issue remains with the implicit conversion:

On a 64-bit platform (sizeof(long)=64):

>>> c.printf("%d\n",1<<64)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ctypes.ArgumentError: argument 2: <type 'exceptions.OverflowError'>: long int too long to convert

so it does do overflow checking, but

>>> c.printf("%d\n",(1<<64)-1)
-1
3
>>> c.printf("%d\n",(1<<32))
0
2

[theller]

I must say I do not care too much about the remaining issue. To be portable between 32-bit and 64-bit platforms you should define .argtypes anyway or explicitely wrap the arguments into ctypes instances, if setting .argtypes is not possible as for printf.