Wrong size of c_ulong/c_ulonglong in Linux

[dudekw]

Bug report

Bug description:

Attribute _type_ of c_ulong returns L, which is correct following the format characters documentation; however, the documentation says it has 4 bytes size, but sizeof(c_ulong) returns 8 bytes.

>>> sizeof(c_ulong)
8
>>> c_ulong._type_
'L'

Also c_ulonglong is automatically casted to c_ulong:

t5=c_ulonglong(200000000000000000000000000000000000)
>>> type(t5)
<class 'ctypes.c_ulong'>

, thus if c_ulong will have 4 bytes, will be there available a type of 8 bytes size?

CPython versions tested on:

3.8

Operating systems tested on:

Linux

Linked PRs

• gh-108907: ctypes: Document _type_ codes #145837
• [3.14] gh-108907: ctypes: Document _type_ codes (GH-145837) #146328

[serhiy-storchaka]

The ‘Standard size’ column refers to the size of the packed value in bytes when using standard size; that is, when the format string starts with one of '<', '>', '!' or '='. When using native size, the size of the packed value is platform-dependent.

[terryjreedy]

_type_ is apparently an attribute of each fundamental data type but unlike value, not of the base class _SimpleCData. Hence it is undocumented in this section. I think it should be, with a mention that the 'types' are 1 char strings from struct Format Characters(I am assuming this) -- with 'native' rather than 'standard' size implied. (I have no idea whether the above has always been true or if type is an addition.)

_type_ is only mentioned in Arrays and Pointers as "Specifies the type ..." with no indication as to what such specification consists of.

[ronaldoussoren]

IMHO there is no bug here, other than the documentation issue mentioned by @terryjreedy.

c_ulong and c_ulonglong are documented as being representations of the C types unsigned long and unsigned long long. As such they'll have the size of associated with those types. 64-bit Linux systems generally use a LP64 model where unsigned long and unsigned long long are both 64-bit bit integers, and hence c_ulong and c_ulonglong are the same type. On 32-bit systems unsigned long is generally a 32-bit quantity, and hence c_ulong and c_ulonglong won't. be the same type there.

[encukou]

Docs are updated.

the 'types' are 1 char strings from struct Format Characters(I am assuming this) -- with 'native' rather than 'standard' size implied. (I have no idea whether the above has always been true or if type is an addition.)

I've kept these -- and array -- separate. There are some differences, but if you're reading about one individual module it's better to get the full table than “X but with Y rather than Z”.