16.16. ctypes — 用于 Python 的外来函数库 ¶

16.16.1.1. 加载 DLL (动态链接库) ¶

ctypes 导出 cdll ，Windows windll and oledll 对象，为加载 DLL (动态链接库)。

通过把库作为这些对象的属性进行访问，加载库。 cdll 加载库，其导出函数使用标准 cdecl 调用约定，而 windll 库调用函数使用 stdcall 调用约定。 oledll 也使用 stdcall 调用约定，并假定函数返回 Windows HRESULT 错误代码。错误代码被用于自动引发 OSError 异常，当函数调用失败时。

这里是一些 Windows 范例。注意： msvcrt 是包含大多数标准 C 函数的 MS 标准 C 库，且使用 cdecl 调用约定：

>>> from ctypes import *
>>> print(windll.kernel32)
<WinDLL 'kernel32', handle ... at ...>
>>> print(cdll.msvcrt)
<CDLL 'msvcrt', handle ... at ...>
>>> libc = cdll.msvcrt
>>>
									

Windows 追加通常 .dll 文件后缀，自动地。

在 Linux，必需指定文件名 包括 扩展名以加载库，因此不可以使用属性访问去加载库。 LoadLibrary() 方法的 DLL 加载程序应该被使用，或应该通过调用构造函数，创建 CDLL 实例加载库：

>>> cdll.LoadLibrary("libc.so.6")
<CDLL 'libc.so.6', handle ... at ...>
>>> libc = CDLL("libc.so.6")
>>> libc
<CDLL 'libc.so.6', handle ... at ...>
>>>
									

16.16.1.2. 访问加载 DLL 的函数 ¶

函数作为 DLL 对象的属性被访问：

>>> from ctypes import *
>>> libc.printf
<_FuncPtr object at 0x...>
>>> print(windll.kernel32.GetModuleHandleA)
<_FuncPtr object at 0x...>
>>> print(windll.kernel32.MyOwnFunction)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "ctypes.py", line 239, in __getattr__
    func = _StdcallFuncPtr(name, self)
AttributeError: function 'MyOwnFunction' not found
>>>
									

注意：win32 系统 DLL 像 kernel32 and user32 often export ANSI as well as UNICODE versions of a function. The UNICODE version is exported with an W 追加到名称，而导出的 ANSI 版本带 A 追加到名称。win32 GetModuleHandle 函数，其返回 module handle 为给定模块名，拥有以下 C 原型，且宏被用于曝光它们之一因为 GetModuleHandle 取决于 UNICODE 是否被定义：

/* ANSI version */
HMODULE GetModuleHandleA(LPCSTR lpModuleName);
/* UNICODE version */
HMODULE GetModuleHandleW(LPCWSTR lpModuleName);
									

windll 不会试着通过 Magic (魔法) 选择它们之一，您必须访问所需版本通过指定 GetModuleHandleA or GetModuleHandleW 明确，然后分别采用字节或字符串对象调用它。

有时，DLL 导出函数采用的名称不是有效 Python 标识符，像 "??2@YAPAXI@Z" 。在这种情况下，必须使用 getattr() 去检索函数：

>>> getattr(cdll.msvcrt, "??2@YAPAXI@Z")
<_FuncPtr object at 0x...>
>>>
									

On Windows, some dlls export functions not by name but by ordinal. These functions can be accessed by indexing the dll object with the ordinal number:

>>> cdll.kernel32[1]
<_FuncPtr object at 0x...>
>>> cdll.kernel32[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "ctypes.py", line 310, in __getitem__
    func = _StdcallFuncPtr(name, self)
AttributeError: function ordinal 0 not found
>>>
									

16.16.1.3. 调用函数 ¶

可以像调用任何其它 Python 回调一样，调用这些函数。此范例使用 time() 函数，其返回自 Unix 纪元以来的系统时间 (以秒为单位)，而 GetModuleHandleA() 函数，其返回 win32 模块句柄。

此范例采用 NULL 指针调用 2 函数 ( None 应该被用作 NULL 指针)：

>>> print(libc.time(None))
1150640792
>>> print(hex(windll.kernel32.GetModuleHandleA(None)))
0x1d000000
>>>
									

ValueError 被引发当调用 stdcall 函数采用 cdecl 调用约定，反之亦然：

>>> cdll.kernel32.GetModuleHandleA(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Procedure probably called with not enough arguments (4 bytes missing)
>>>
>>> windll.msvcrt.printf(b"spam")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Procedure probably called with too many arguments (4 bytes in excess)
>>>
									

要找出正确调用约定，必须查看 C 头文件 (或希望调用的函数文档编制)。

在 Windows， ctypes 使用 win32 结构化异常处理去预防来自一般保护故障的崩溃，当函数采用无效自变量值被调用时：

>>> windll.kernel32.GetModuleHandleA(32)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: exception: access violation reading 0x00000020
>>>
									

不管怎样，有足够的办法崩溃 Python 采用 ctypes ，所以无论如何都要小心。 faulthandler 模块有助于调试崩溃 (如：由不正确 C 库调用产生的分段故障)。

None 、整数、字节对象及 (unicode) 字符串是唯一本机 Python 对象，可以被直接用作这些函数调用的参数。 None 被传递作为 C NULL 指针，字节对象和字符串被传递作为指向包含其数据的内存块的指针 ( char * or wchar_t * )。Python 整数被传递作为平台默认 C int 类型。它们的值被屏蔽以拟合成 C 类型。

在继续采用其它参数类型调用函数之前，必须了解更多有关 ctypes 数据类型。

16.16.1.4. 基础数据类型 ¶

ctypes 定义了许多首要 C 兼容数据类型：

1. 构造函数接受具有真值的任何对象。

所有这些类型可以被创建，通过采用正确类型的可选初始化程序和值调用它们：

>>> c_int()
c_long(0)
>>> c_wchar_p("Hello, World")
c_wchar_p(140018365411392)
>>> c_ushort(-3)
c_ushort(65533)
>>>
									

由于这些类型是可变的，它们的值也可以在之后改变：

>>> i = c_int(42)
>>> print(i)
c_long(42)
>>> print(i.value)
42
>>> i.value = -99
>>> print(i.value)
-99
>>>
									

把新值赋值给指针实例，为类型 c_char_p , c_wchar_p ，和 c_void_p 改变 内存定位 指向， 不是内容 的内存块 (当然不是，因为 Python 字节对象是不可变的)：

>>> s = "Hello, World"
>>> c_s = c_wchar_p(s)
>>> print(c_s)
c_wchar_p(139966785747344)
>>> print(c_s.value)
Hello World
>>> c_s.value = "Hi, there"
>>> print(c_s)              # the memory location has changed
c_wchar_p(139966783348904)
>>> print(c_s.value)
Hi, there
>>> print(s)                # first object is unchanged
Hello, World
>>>
									

You should be careful, however, not to pass them to functions expecting pointers to mutable memory. If you need mutable memory blocks, ctypes has a create_string_buffer() function which creates these in various ways. The current memory block contents can be accessed (or changed) with the raw 特性；若希望以 NULL 终止字符串方式访问它，请使用 value 特性：

>>> from ctypes import *
>>> p = create_string_buffer(3)            # create a 3 byte buffer, initialized to NUL bytes
>>> print(sizeof(p), repr(p.raw))
3 b'\x00\x00\x00'
>>> p = create_string_buffer(b"Hello")     # create a buffer containing a NUL terminated string
>>> print(sizeof(p), repr(p.raw))
6 b'Hello\x00'
>>> print(repr(p.value))
b'Hello'
>>> p = create_string_buffer(b"Hello", 10) # create a 10 byte buffer
>>> print(sizeof(p), repr(p.raw))
10 b'Hello\x00\x00\x00\x00\x00'
>>> p.value = b"Hi"
>>> print(sizeof(p), repr(p.raw))
10 b'Hi\x00lo\x00\x00\x00\x00\x00'
>>>
									

create_string_buffer() 函数替换 c_buffer() 函数 (仍然可以用作别名)，及 c_string() function from earlier ctypes releases. To create a mutable memory block containing unicode characters of the C type wchar_t 使用 create_unicode_buffer() 函数。

16.16.1.5. 调用函数，继续 ¶

注意：printf 打印到真正的标准输出通道， not to sys.stdout ，因此，这些范例将仅工作于控制台提示，而不是 IDLE or PythonWin :

>>> printf = libc.printf
>>> printf(b"Hello, %s\n", b"World!")
Hello, World!
14
>>> printf(b"Hello, %S\n", "World!")
Hello, World!
14
>>> printf(b"%d bottles of beer\n", 42)
42 bottles of beer
19
>>> printf(b"%f bottles of beer\n", 42.5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ArgumentError: argument 2: exceptions.TypeError: Don't know how to convert parameter 2
>>>
									

如前所述，除整数、字符串及 bytes 对象外，所有 Python 类型都必须包裹在其相应 ctypes 类型，以便它们被转换成所需的 C 数据类型：

>>> printf(b"An int %d, a double %f\n", 1234, c_double(3.14))
An int 1234, a double 3.140000
31
>>>
									

16.16.1.6. 调用函数采用您自己的自定义数据类型 ¶

也可以定制 ctypes 自变量转换，以允许您自己的类实例被用作函数自变量。 ctypes 寻找 _as_parameter_ attribute and uses this as the function argument. Of course, it must be one of integer, string, or bytes:

>>> class Bottles:
...     def __init__(self, number):
...         self._as_parameter_ = number
...
>>> bottles = Bottles(42)
>>> printf(b"%d bottles of beer\n", bottles)
42 bottles of beer
19
>>>
									

若不想把实例数据存储在 _as_parameter_ 实例变量，您可以定义 property 使属性在请求时可用。

16.16.1.7. 指定所需的自变量类型 (函数原型) ¶

指定从 DLL 导出函数所需的自变量类型是可能的，通过设置 argtypes 属性。

argtypes 必须是 C 数据类型序列 ( printf 函数在此或许不是好范例，因为它接受可变数和取决于格式字符串的不同参数类型，另一方面，这对采用此特征进行试验是非常顺手的)：

>>> printf.argtypes = [c_char_p, c_char_p, c_int, c_double]
>>> printf(b"String '%s', Int %d, Double %f\n", b"Hi", 10, 2.2)
String 'Hi', Int 10, Double 2.200000
37
>>>
									

指定格式保护不兼容自变量类型 (就像 C 函数原型)，并试着把自变量转换成有效类型：

>>> printf(b"%d %d %d", 1, 2, 3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ArgumentError: argument 2: exceptions.TypeError: wrong type
>>> printf(b"%s %d %f\n", b"X", 2, 3)
X 2 3.000000
13
>>>
									

If you have defined your own classes which you pass to function calls, you have to implement a from_param() class method for them to be able to use them in the argtypes sequence. The from_param() class method receives the Python object passed to the function call, it should do a typecheck or whatever is needed to make sure this object is acceptable, and then return the object itself, its _as_parameter_ attribute, or whatever you want to pass as the C function argument in this case. Again, the result should be an integer, string, bytes, a ctypes instance, or an object with an _as_parameter_ 属性。

16.16.1.8. 返回类型 ¶

默认情况下，假定函数返回 C int 类型。其它返回类型可以被指定，通过设置 restype 属性为函数对象。

这里是更高级范例，它使用 strchr 函数，其期望字符串指针和 char，并返回指向字符串的指针：

>>> strchr = libc.strchr
>>> strchr(b"abcdef", ord("d"))
8059983
>>> strchr.restype = c_char_p    # c_char_p is a pointer to a string
>>> strchr(b"abcdef", ord("d"))
b'def'
>>> print(strchr(b"abcdef", ord("x")))
None
>>>
									

If you want to avoid the ord("x") calls above, you can set the argtypes attribute, and the second argument will be converted from a single character Python bytes object into a C char:

>>> strchr.restype = c_char_p
>>> strchr.argtypes = [c_char_p, c_char]
>>> strchr(b"abcdef", b"d")
'def'
>>> strchr(b"abcdef", b"def")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ArgumentError: argument 2: exceptions.TypeError: one character string expected
>>> print(strchr(b"abcdef", b"x"))
None
>>> strchr(b"abcdef", b"d")
'def'
>>>
									

You can also use a callable Python object (a function or a class for example) as the restype attribute, if the foreign function returns an integer. The callable will be called with the integer the C function returns, and the result of this call will be used as the result of your function call. This is useful to check for error return values and automatically raise an exception:

>>> GetModuleHandle = windll.kernel32.GetModuleHandleA
>>> def ValidHandle(value):
...     if value == 0:
...         raise WinError()
...     return value
...
>>>
>>> GetModuleHandle.restype = ValidHandle
>>> GetModuleHandle(None)
486539264
>>> GetModuleHandle("something silly")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in ValidHandle
OSError: [Errno 126] The specified module could not be found.
>>>
									

WinError is a function which will call Windows FormatMessage() api to get the string representation of an error code, and 返回 an exception. WinError takes an optional error code parameter, if no one is used, it calls GetLastError() to retrieve it.

Please note that a much more powerful error checking mechanism is available through the errcheck attribute; see the reference manual for details.

16.16.1.9. 传递指针 (或：通过引用传递参数) ¶

Sometimes a C api function expects a pointer to a data type as parameter, probably to write into the corresponding location, or if the data is too large to be passed by value. This is also known as 通过引用传递参数 .

ctypes 导出 byref() function which is used to pass parameters by reference. The same effect can be achieved with the pointer() function, although pointer() does a lot more work since it constructs a real pointer object, so it is faster to use byref() if you don’t need the pointer object in Python itself:

>>> i = c_int()
>>> f = c_float()
>>> s = create_string_buffer(b'\000' * 32)
>>> print(i.value, f.value, repr(s.value))
0 0.0 b''
>>> libc.sscanf(b"1 3.14 Hello", b"%d %f %s",
...             byref(i), byref(f), s)
3
>>> print(i.value, f.value, repr(s.value))
1 3.1400001049 b'Hello'
>>>
									

16.16.1.10. Structure 和 Union ¶

Structure 和 Union 必须派生自 Structure and Union 基类，其被定义在 ctypes 模块。每个子类必须定义 _fields_ 属性。 _fields_ 必须是列表 2-tuples ，包含 field name 和 field type .

字段类型必须是 ctypes 类型像 c_int ，或任何其它派生 ctypes 类：Structure、Union、Array、Pointer。

这里是简单 POINT 结构范例，其包含 2 个整数，名为 x and y ，并展示如何在构造函数中初始化结构：

>>> from ctypes import *
>>> class POINT(Structure):
...     _fields_ = [("x", c_int),
...                 ("y", c_int)]
...
>>> point = POINT(10, 20)
>>> print(point.x, point.y)
10 20
>>> point = POINT(y=5)
>>> print(point.x, point.y)
0 5
>>> POINT(1, 2, 3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: too many initializers
>>>
									

You can, however, build much more complicated structures. A structure can itself contain other structures by using a structure as a field type.

Here is a RECT structure which contains two POINTs named upperleft and lowerright :

>>> class RECT(Structure):
...     _fields_ = [("upperleft", POINT),
...                 ("lowerright", POINT)]
...
>>> rc = RECT(point)
>>> print(rc.upperleft.x, rc.upperleft.y)
0 5
>>> print(rc.lowerright.x, rc.lowerright.y)
0 0
>>>
									

Nested structures can also be initialized in the constructor in several ways:

>>> r = RECT(POINT(1, 2), POINT(3, 4))
>>> r = RECT((1, 2), (3, 4))
									

字段 descriptor s can be retrieved from the class , they are useful for debugging because they can provide useful information:

>>> print(POINT.x)
<Field type=c_long, ofs=0, size=4>
>>> print(POINT.y)
<Field type=c_long, ofs=4, size=4>
>>>
									

16.16.1.11. Structure/Union 对齐和字节序 ¶

By default, Structure and Union fields are aligned in the same way the C compiler does it. It is possible to override this behavior be specifying a _pack_ class attribute in the subclass definition. This must be set to a positive integer and specifies the maximum alignment for the fields. This is what #pragma pack(n) also does in MSVC.

ctypes uses the native byte order for Structures and Unions. To build structures with non-native byte order, you can use one of the BigEndianStructure , LittleEndianStructure , BigEndianUnion ，和 LittleEndianUnion base classes. These classes cannot contain pointer fields.

16.16.1.12. 在 Structure 和 Union 中的位字段 ¶

It is possible to create structures and unions containing bit fields. Bit fields are only possible for integer fields, the bit width is specified as the third item in the _fields_ tuples:

>>> class Int(Structure):
...     _fields_ = [("first_16", c_int, 16),
...                 ("second_16", c_int, 16)]
...
>>> print(Int.first_16)
<Field type=c_long, ofs=0:0, bits=16>
>>> print(Int.second_16)
<Field type=c_long, ofs=0:16, bits=16>
>>>
									

16.16.1.13. 数组 ¶

Arrays are sequences, containing a fixed number of instances of the same type.

The recommended way to create array types is by multiplying a data type with a positive integer:

TenPointsArrayType = POINT * 10
									

Here is an example of a somewhat artificial data type, a structure containing 4 POINTs among other stuff:

>>> from ctypes import *
>>> class POINT(Structure):
...     _fields_ = ("x", c_int), ("y", c_int)
...
>>> class MyStruct(Structure):
...     _fields_ = [("a", c_int),
...                 ("b", c_float),
...                 ("point_array", POINT * 4)]
>>>
>>> print(len(MyStruct().point_array))
4
>>>
									

Instances are created in the usual way, by calling the class:

arr = TenPointsArrayType()
for pt in arr:
    print(pt.x, pt.y)
									

The above code print a series of 0 0 lines, because the array contents is initialized to zeros.

Initializers of the correct type can also be specified:

>>> from ctypes import *
>>> TenIntegers = c_int * 10
>>> ii = TenIntegers(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
>>> print(ii)
<c_long_Array_10 object at 0x...>
>>> for i in ii: print(i, end=" ")
...
1 2 3 4 5 6 7 8 9 10
>>>
									

16.16.1.14. 指针 ¶

指针实例被创建，通过调用 pointer() 函数在 ctypes 类型：

>>> from ctypes import *
>>> i = c_int(42)
>>> pi = pointer(i)
>>>
									

Pointer instances have a contents attribute which returns the object to which the pointer points, the i object above:

>>> pi.contents
c_long(42)
>>>
									

注意， ctypes does not have OOR (original object return), it constructs a new, equivalent object each time you retrieve an attribute:

>>> pi.contents is i
False
>>> pi.contents is pi.contents
False
>>>
									

Assigning another c_int instance to the pointer’s contents attribute would cause the pointer to point to the memory location where this is stored:

>>> i = c_int(99)
>>> pi.contents = i
>>> pi.contents
c_long(99)
>>>
									

Pointer instances can also be indexed with integers:

>>> pi[0]
99
>>>
									

Assigning to an integer index changes the pointed to value:

>>> print(i)
c_long(99)
>>> pi[0] = 22
>>> print(i)
c_long(22)
>>>
									

It is also possible to use indexes different from 0, but you must know what you’re doing, just as in C: You can access or change arbitrary memory locations. Generally you only use this feature if you receive a pointer from a C function, and you know that the pointer actually points to an array instead of a single item.

Behind the scenes, the pointer() function does more than simply create pointer instances, it has to create pointer types first. This is done with the POINTER() function, which accepts any ctypes type, and returns a new type:

>>> PI = POINTER(c_int)
>>> PI
<class 'ctypes.LP_c_long'>
>>> PI(42)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: expected c_long instead of int
>>> PI(c_int(42))
<ctypes.LP_c_long object at 0x...>
>>>
									

Calling the pointer type without an argument creates a NULL pointer. NULL pointers have a False boolean value:

>>> null_ptr = POINTER(c_int)()
>>> print(bool(null_ptr))
False
>>>
									

ctypes checks for NULL when dereferencing pointers (but dereferencing invalid non- NULL pointers would crash Python):

>>> null_ptr[0]
Traceback (most recent call last):
    ....
ValueError: NULL pointer access
>>>
>>> null_ptr[0] = 1234
Traceback (most recent call last):
    ....
ValueError: NULL pointer access
>>>
									

16.16.1.15. 类型转换 ¶

Usually, ctypes does strict type checking. This means, if you have POINTER(c_int) 在 argtypes list of a function or as the type of a member field in a structure definition, only instances of exactly the same type are accepted. There are some exceptions to this rule, where ctypes accepts other objects. For example, you can pass compatible array instances instead of pointer types. So, for POINTER(c_int) , ctypes accepts an array of c_int:

>>> class Bar(Structure):
...     _fields_ = [("count", c_int), ("values", POINTER(c_int))]
...
>>> bar = Bar()
>>> bar.values = (c_int * 3)(1, 2, 3)
>>> bar.count = 3
>>> for i in range(bar.count):
...     print(bar.values[i])
...
1
2
3
>>>
									

In addition, if a function argument is explicitly declared to be a pointer type (such as POINTER(c_int) ) in argtypes , an object of the pointed type ( c_int in this case) can be passed to the function. ctypes will apply the required byref() conversion in this case automatically.

To set a POINTER type field to NULL , you can assign None :

>>> bar.values = None
>>>
									

Sometimes you have instances of incompatible types. In C, you can cast one type into another type. ctypes 提供 cast() function which can be used in the same way. The Bar structure defined above accepts POINTER(c_int) pointers or c_int arrays for its values field, but not instances of other types:

>>> bar.values = (c_byte * 4)()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: incompatible types, c_byte_Array_4 instance instead of LP_c_long instance
>>>
									

For these cases, the cast() function is handy.

cast() function can be used to cast a ctypes instance into a pointer to a different ctypes data type. cast() takes two parameters, a ctypes object that is or can be converted to a pointer of some kind, and a ctypes pointer type. It returns an instance of the second argument, which references the same memory block as the first argument:

>>> a = (c_byte * 4)()
>>> cast(a, POINTER(c_int))
<ctypes.LP_c_long object at ...>
>>>
									

So, cast() can be used to assign to the values field of Bar the structure:

>>> bar = Bar()
>>> bar.values = cast((c_byte * 4)(), POINTER(c_int))
>>> print(bar.values[0])
0
>>>
									

16.16.1.16. 不完整类型 ¶

Incomplete Types are structures, unions or arrays whose members are not yet specified. In C, they are specified by forward declarations, which are defined later:

struct cell; /* forward declaration */
struct cell {
    char *name;
    struct cell *next;
};
									

The straightforward translation into ctypes code would be this, but it does not work:

>>> class cell(Structure):
...     _fields_ = [("name", c_char_p),
...                 ("next", POINTER(cell))]
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in cell
NameError: name 'cell' is not defined
>>>
									

because the new class cell is not available in the class statement itself. In ctypes , we can define the cell class and set the _fields_ attribute later, after the class statement:

>>> from ctypes import *
>>> class cell(Structure):
...     pass
...
>>> cell._fields_ = [("name", c_char_p),
...                  ("next", POINTER(cell))]
>>>
									

Lets try it. We create two instances of cell , and let them point to each other, and finally follow the pointer chain a few times:

>>> c1 = cell()
>>> c1.name = "foo"
>>> c2 = cell()
>>> c2.name = "bar"
>>> c1.next = pointer(c2)
>>> c2.next = pointer(c1)
>>> p = c1
>>> for i in range(8):
...     print(p.name, end=" ")
...     p = p.next[0]
...
foo bar foo bar foo bar foo bar
>>>
									

16.16.1.17. 回调函数 ¶

ctypes allows creating C callable function pointers from Python callables. These are sometimes called 回调函数 .

First, you must create a class for the callback function. The class knows the calling convention, the return type, and the number and types of arguments this function will receive.

CFUNCTYPE() 工厂函数为回调函数创建类型，使用 cdecl 调用约定。在 Windows， WINFUNCTYPE() 工厂函数为回调函数创建类型，使用 stdcall 调用约定。

这 2 工厂函数采用结果类型作为第一自变量被调用，而回调函数把期望自变量类型作为剩余自变量。

此处将呈现的范例，使用标准 C 库的 qsort() 函数，用于在回调函数的帮助下对项进行排序。 qsort() 将被用于对整数数组进行排序：

>>> IntArray5 = c_int * 5
>>> ia = IntArray5(5, 1, 7, 33, 99)
>>> qsort = libc.qsort
>>> qsort.restype = None
>>>
									

qsort() must be called with a pointer to the data to sort, the number of items in the data array, the size of one item, and a pointer to the comparison function, the callback. The callback will then be called with two pointers to items, and it must return a negative integer if the first item is smaller than the second, a zero if they are equal, and a positive integer otherwise.

因此，回调函数接收指向整数的指针，且必须返回整数。首先，我们创建 type 为回调函数：

>>> CMPFUNC = CFUNCTYPE(c_int, POINTER(c_int), POINTER(c_int))
>>>
									

开始，这里是展示它获取传递值的简单回调：

>>> def py_cmp_func(a, b):
...     print("py_cmp_func", a[0], b[0])
...     return 0
...
>>> cmp_func = CMPFUNC(py_cmp_func)
>>>
									

结果：

>>> qsort(ia, len(ia), sizeof(c_int), cmp_func)
py_cmp_func 5 1
py_cmp_func 33 99
py_cmp_func 7 33
py_cmp_func 5 7
py_cmp_func 1 7
>>>
									

现在，我们可以实际比较 2 项并返回有用结果：

>>> def py_cmp_func(a, b):
...     print("py_cmp_func", a[0], b[0])
...     return a[0] - b[0]
...
>>>
>>> qsort(ia, len(ia), sizeof(c_int), CMPFUNC(py_cmp_func))
py_cmp_func 5 1
py_cmp_func 33 99
py_cmp_func 7 33
py_cmp_func 1 7
py_cmp_func 5 7
>>>
									

正如可以轻松校验那样，我们现在对数组进行排序：

>>> for i in ia: print(i, end=" ")
...
1 5 7 33 99
>>>
									

函数工厂可以被用作装饰器工厂，因此也可以这样写：

>>> @CFUNCTYPE(c_int, POINTER(c_int), POINTER(c_int))
... def py_cmp_func(a, b):
...     print("py_cmp_func", a[0], b[0])
...     return a[0] - b[0]
...
>>> qsort(ia, len(ia), sizeof(c_int), py_cmp_func)
py_cmp_func 5 1
py_cmp_func 33 99
py_cmp_func 7 33
py_cmp_func 1 7
py_cmp_func 5 7
>>>
									

16.16.1.18. 访问 DLL 导出值 ¶

Some shared libraries not only export functions, they also export variables. An example in the Python library itself is the Py_OptimizeFlag , an integer set to 0, 1, or 2, depending on the -O or -OO flag given on startup.

ctypes can access values like this with the in_dll() class methods of the type. pythonapi is a predefined symbol giving access to the Python C api:

>>> opt_flag = c_int.in_dll(pythonapi, "Py_OptimizeFlag")
>>> print(opt_flag)
c_long(0)
>>>
									

If the interpreter would have been started with -O , the sample would have printed c_long(1) ，或 c_long(2) if -OO would have been specified.

An extended example which also demonstrates the use of pointers accesses the PyImport_FrozenModules pointer exported by Python.

Quoting the docs for that value:

This pointer is initialized to point to an array of struct _frozen records, terminated by one whose members are all NULL or zero. When a frozen module is imported, it is searched in this table. Third-party code could play tricks with this to provide a dynamically created collection of frozen modules.

So manipulating this pointer could even prove useful. To restrict the example size, we show only how this table can be read with ctypes :

>>> from ctypes import *
>>>
>>> class struct_frozen(Structure):
...     _fields_ = [("name", c_char_p),
...                 ("code", POINTER(c_ubyte)),
...                 ("size", c_int)]
...
>>>
									

We have defined the struct _frozen data type, so we can get the pointer to the table:

>>> FrozenTable = POINTER(struct_frozen)
>>> table = FrozenTable.in_dll(pythonapi, "PyImport_FrozenModules")
>>>
									

Since table 是 pointer to the array of struct_frozen records, we can iterate over it, but we just have to make sure that our loop terminates, because pointers have no size. Sooner or later it would probably crash with an access violation or whatever, so it’s better to break out of the loop when we hit the NULL entry:

>>> for item in table:
...     if item.name is None:
...         break
...     print(item.name.decode("ascii"), item.size)
...
_frozen_importlib 31764
_frozen_importlib_external 41499
__hello__ 161
__phello__ -161
__phello__.spam 161
>>>
									

The fact that standard Python has a frozen module and a frozen package (indicated by the negative size member) is not well known, it is only used for testing. Try it out with import __hello__ 例如。

16.16.1.19. Surprises ¶

There are some edges in ctypes where you might expect something other than what actually happens.

Consider the following example:

>>> from ctypes import *
>>> class POINT(Structure):
...     _fields_ = ("x", c_int), ("y", c_int)
...
>>> class RECT(Structure):
...     _fields_ = ("a", POINT), ("b", POINT)
...
>>> p1 = POINT(1, 2)
>>> p2 = POINT(3, 4)
>>> rc = RECT(p1, p2)
>>> print(rc.a.x, rc.a.y, rc.b.x, rc.b.y)
1 2 3 4
>>> # now swap the two points
>>> rc.a, rc.b = rc.b, rc.a
>>> print(rc.a.x, rc.a.y, rc.b.x, rc.b.y)
3 4 3 4
>>>
									

Hm. We certainly expected the last statement to print 3 4 1 2 . What happened? Here are the steps of the rc.a, rc.b = rc.b, rc.a line above:

>>> temp0, temp1 = rc.b, rc.a
>>> rc.a = temp0
>>> rc.b = temp1
>>>
									

注意， temp0 and temp1 are objects still using the internal buffer of the rc object above. So executing rc.a = temp0 copies the buffer contents of temp0 into rc ‘s buffer. This, in turn, changes the contents of temp1 . So, the last assignment rc.b = temp1 , doesn’t have the expected effect.

Keep in mind that retrieving sub-objects from Structure, Unions, and Arrays doesn’t copy the sub-object, instead it retrieves a wrapper object accessing the root-object’s underlying buffer.

Another example that may behave different from what one would expect is this:

>>> s = c_char_p()
>>> s.value = "abc def ghi"
>>> s.value
'abc def ghi'
>>> s.value is s.value
False
>>>
									

Why is it printing False ? ctypes instances are objects containing a memory block plus some descriptor s accessing the contents of the memory. Storing a Python object in the memory block does not store the object itself, instead the contents of the object is stored. Accessing the contents again constructs a new Python object each time!

16.16.1.20. 可变大小的数据类型 ¶

ctypes provides some support for variable-sized arrays and structures.

resize() function can be used to resize the memory buffer of an existing ctypes object. The function takes the object as first argument, and the requested size in bytes as the second argument. The memory block cannot be made smaller than the natural memory block specified by the objects type, a ValueError is raised if this is tried:

>>> short_array = (c_short * 4)()
>>> print(sizeof(short_array))
8
>>> resize(short_array, 4)
Traceback (most recent call last):
    ...
ValueError: minimum size is 8
>>> resize(short_array, 32)
>>> sizeof(short_array)
32
>>> sizeof(type(short_array))
8
>>>
									

This is nice and fine, but how would one access the additional elements contained in this array? Since the type still only knows about 4 elements, we get errors accessing other elements:

>>> short_array[:]
[0, 0, 0, 0]
>>> short_array[7]
Traceback (most recent call last):
    ...
IndexError: invalid index
>>>
									

Another way to use variable-sized data types with ctypes is to use the dynamic nature of Python, and (re-)define the data type after the required size is already known, on a case by case basis.

16.16.2.1. 查找共享库 ¶

以编译语言编程时，在编译/链接程序及程序运行时共享库会被访问。

The purpose of the find_library() function is to locate a library in a way similar to what the compiler or runtime loader does (on platforms with several versions of a shared library the most recent should be loaded), while the ctypes library loaders act like when a program is run, and call the runtime loader directly.

ctypes.util module provides a function which can help to determine the library to load.

ctypes.util. find_library ( name )

Try to find a library and return a pathname. name is the library name without any prefix like lib , suffix like .so , .dylib or version number (this is the form used for the posix linker option -l ). If no library can be found, returns None .

确切功能从属系统。

在 Linux， find_library() tries to run external programs ( /sbin/ldconfig , gcc , objdump and ld ) to find the library file. It returns the filename of the library file.

这里是一些范例：

>>> from ctypes.util import find_library
>>> find_library("m")
'libm.so.6'
>>> find_library("c")
'libc.so.6'
>>> find_library("bz2")
'libbz2.so.1.0'
>>>
									

在 OS X， find_library() tries several predefined naming schemes and paths to locate the library, and returns a full pathname if successful:

>>> from ctypes.util import find_library
>>> find_library("c")
'/usr/lib/libc.dylib'
>>> find_library("m")
'/usr/lib/libm.dylib'
>>> find_library("bz2")
'/usr/lib/libbz2.dylib'
>>> find_library("AGL")
'/System/Library/Frameworks/AGL.framework/AGL'
>>>
									

在 Windows， find_library() searches along the system search path, and returns the full pathname, but since there is no predefined naming scheme a call like find_library("c") will fail and return None .

If wrapping a shared library with ctypes , it may be better to determine the shared library name at development time, and hardcode that into the wrapper module instead of using find_library() to locate the library at runtime.

16.16.2.2. 加载共享库 ¶

There are several ways to load shared libraries into the Python process. One way is to instantiate one of the following classes:

class ctypes. CDLL ( name , mode=DEFAULT_MODE , handle=None , use_errno=False , use_last_error=False ) ¶

Instances of this class represent loaded shared libraries. Functions in these libraries use the standard C calling convention, and are assumed to return int .

class ctypes. OleDLL ( name , mode=DEFAULT_MODE , handle=None , use_errno=False , use_last_error=False ) ¶

仅 Windows：此类的实例表示被加载的共享库，这些库中的函数使用 stdcall 调用约定，并假定返回 Windows 特定 HRESULT 代码。 HRESULT values contain information specifying whether the function call failed or succeeded, together with additional error code. If the return value signals a failure, an OSError 被自动引发。

3.3 版改变： WindowsError 被用于引发。

class ctypes. WinDLL ( name , mode=DEFAULT_MODE , handle=None , use_errno=False , use_last_error=False ) ¶

仅 Windows：此类的实例表示被加载的共享库，这些库中的函数使用 stdcall 调用约定，并假定返回 int 在默认情况下。

Windows CE 仅使用标准调用约定，为方便起见 WinDLL and OleDLL 在此平台使用标准调用约定。

Python 全局解释器锁 会被释放在调用由这些库导出的任何函数之前，和之后重新获取。

class ctypes. PyDLL ( name , mode=DEFAULT_MODE , handle=None ) ¶

此类的实例行为像 CDLL 实例，除了 Python GIL not released during the function call, and after the function execution the Python error flag is checked. If the error flag is set, a Python exception is raised.

因此，这只对直接调用 Python C API 函数有用。

All these classes can be instantiated by calling them with at least one argument, the pathname of the shared library. If you have an existing handle to an already loaded shared library, it can be passed as the handle 命名参数，否则底层平台 dlopen or LoadLibrary 函数被用于把库加载到进程中，并获取其句柄。

mode 参数可以被用于指定如何加载库。有关细节，请翻阅 dlopen(3) 手册页。在 Windows， mode 被忽略。在 POSIX 系统，RTLD_NOW 被始终添加，且不可配置。

use_errno parameter, when set to true, enables a ctypes mechanism that allows accessing the system errno error number in a safe way. ctypes maintains a thread-local copy of the systems errno variable; if you call foreign functions created with use_errno=True then the errno value before the function call is swapped with the ctypes private copy, the same happens immediately after the function call.

函数 ctypes.get_errno() returns the value of the ctypes private copy, and the function ctypes.set_errno() changes the ctypes private copy to a new value and returns the former value.

use_last_error parameter, when set to true, enables the same mechanism for the Windows error code which is managed by the GetLastError() and SetLastError() Windows API functions; ctypes.get_last_error() and ctypes.set_last_error() are used to request and change the ctypes private copy of the windows error code.

ctypes. RTLD_GLOBAL

Flag to use as mode parameter. On platforms where this flag is not available, it is defined as the integer zero.

ctypes. RTLD_LOCAL

Flag to use as mode parameter. On platforms where this is not available, it is the same as RTLD_GLOBAL .

ctypes. DEFAULT_MODE

The default mode which is used to load shared libraries. On OSX 10.3, this is RTLD_GLOBAL , otherwise it is the same as RTLD_LOCAL .

Instances of these classes have no public methods. Functions exported by the shared library can be accessed as attributes or by index. Please note that accessing the function through an attribute caches the result and therefore accessing it repeatedly returns the same object each time. On the other hand, accessing it through an index returns a new object each time:

>>> libc.time == libc.time
True
>>> libc['time'] == libc['time']
False
									

The following public attributes are available, their name starts with an underscore to not clash with exported function names:

PyDLL. _handle ¶

The system handle used to access the library.

PyDLL. _name ¶

The name of the library passed in the constructor.

Shared libraries can also be loaded by using one of the prefabricated objects, which are instances of the LibraryLoader class, either by calling the LoadLibrary() method, or by retrieving the library as attribute of the loader instance.

class ctypes. LibraryLoader ( dlltype ) ¶

加载共享库的类。 dlltype 应为 CDLL , PyDLL , WinDLL ，或 OleDLL types.

__getattr__() has special behavior: It allows loading a shared library by accessing it as attribute of a library loader instance. The result is cached, so repeated attribute accesses return the same library each time.

LoadLibrary ( name ) ¶

Load a shared library into the process and return it. This method always returns a new instance of the library.

这些预制库加载程序是可用的：

ctypes. cdll

创建 CDLL 实例。

ctypes. windll

仅 Windows：创建 WinDLL 实例。

ctypes. oledll

仅 Windows：创建 OleDLL 实例。

ctypes. pydll

创建 PyDLL 实例。

For accessing the C Python api directly, a ready-to-use Python shared library object is available:

ctypes. pythonapi

An instance of PyDLL that exposes Python C API functions as attributes. Note that all these functions are assumed to return C int , which is of course not always the truth, so you have to assign the correct restype attribute to use these functions.

16.16.2.3. 外来函数 ¶

As explained in the previous section, foreign functions can be accessed as attributes of loaded shared libraries. The function objects created in this way by default accept any number of arguments, accept any ctypes data instances as arguments, and return the default result type specified by the library loader. They are instances of a private class:

class ctypes. _FuncPtr ¶

Base class for C callable foreign functions.

Instances of foreign functions are also C compatible data types; they represent C function pointers.

This behavior can be customized by assigning to special attributes of the foreign function object.

restype ¶

Assign a ctypes type to specify the result type of the foreign function. Use None for void , a function not returning anything.

It is possible to assign a callable Python object that is not a ctypes type, in this case the function is assumed to return a C int , and the callable will be called with this integer, allowing further processing or error checking. Using this is deprecated, for more flexible post processing or error checking use a ctypes data type as restype and assign a callable to the errcheck 属性。

argtypes ¶

Assign a tuple of ctypes types to specify the argument types that the function accepts. Functions using the stdcall calling convention can only be called with the same number of arguments as the length of this tuple; functions using the C calling convention accept additional, unspecified arguments as well.

When a foreign function is called, each actual argument is passed to the from_param() class method of the items in the argtypes tuple, this method allows adapting the actual argument to an object that the foreign function accepts. For example, a c_char_p item in the argtypes tuple will convert a string passed as argument into a bytes object using ctypes conversion rules.

New: It is now possible to put items in argtypes which are not ctypes types, but each item must have a from_param() method which returns a value usable as argument (integer, string, ctypes instance). This allows defining adapters that can adapt custom objects as function parameters.

errcheck ¶

Assign a Python function or another callable to this attribute. The callable will be called with three or more arguments:

callable ( result , func , arguments )

result is what the foreign function returns, as specified by the restype 属性。

func is the foreign function object itself, this allows reusing the same callable object to check or post process the results of several functions.

arguments is a tuple containing the parameters originally passed to the function call, this allows specializing the behavior on the arguments used.

The object that this function returns will be returned from the foreign function call, but it can also check the result value and raise an exception if the foreign function call failed.

exception ctypes. ArgumentError ¶

This exception is raised when a foreign function call cannot convert one of the passed arguments.

16.16.2.4. 函数原型 ¶

Foreign functions can also be created by instantiating function prototypes. Function prototypes are similar to function prototypes in C; they describe a function (return type, argument types, calling convention) without defining an implementation. The factory functions must be called with the desired result type and the argument types of the function, and can be used as decorator factories, and as such, be applied to functions through the @wrapper 句法。见 回调函数 范例。

ctypes. CFUNCTYPE ( restype , *argtypes , use_errno=False , use_last_error=False ) ¶

The returned function prototype creates functions that use the standard C calling convention. The function will release the GIL during the call. If use_errno 被设为 true，ctypes 私有拷贝的系统 errno 变量会被交换与真实 errno 值，在调用前后； use_last_error 对 Windows 错误代码做相同处理。

ctypes. WINFUNCTYPE ( restype , *argtypes , use_errno=False , use_last_error=False ) ¶

仅 Windows：返回的函数原型，创建的函数使用 stdcall 调用约定，除 Windows CE 外，那里 WINFUNCTYPE() 如同 CFUNCTYPE() 。函数在调用期间会释放 GIL。 use_errno and use_last_error 的含义同上。

ctypes. PYFUNCTYPE ( restype , *argtypes ) ¶

返回的函数原型，创建使用Python 调用约定的函数。函数会 not 释放 GIL 在调用期间。

可以按不同方式实例化由这些工厂函数创建的函数原型，取决于调用中的参数类型及参数数量：

prototype ( address )

返回在指定地址的外来函数，地址必须为整数。

prototype ( callable )

创建 C 可调用函数 (回调函数) 从 Python callable .

prototype ( func_spec [ , paramflags ] )

Returns a foreign function exported by a shared library. func_spec must be a 2-tuple (name_or_ordinal, library) . The first item is the name of the exported function as string, or the ordinal of the exported function as small integer. The second item is the shared library instance.

prototype ( vtbl_index , name [ , paramflags [ , iid ] ] )

Returns a foreign function that will call a COM method. vtbl_index is the index into the virtual function table, a small non-negative integer. name is name of the COM method. iid is an optional pointer to the interface identifier which is used in extended error reporting.

COM methods use a special calling convention: They require a pointer to the COM interface as first argument, in addition to those parameters that are specified in the argtypes tuple.

可选 paramflags parameter creates foreign function wrappers with much more functionality than the features described above.

paramflags must be a tuple of the same length as argtypes .

Each item in this tuple contains further information about a parameter, it must be a tuple containing one, two, or three items.

The first item is an integer containing a combination of direction flags for the parameter:

1

Specifies an input parameter to the function.

2

Output parameter. The foreign function fills in a value.

4

Input parameter which defaults to the integer zero.

The optional second item is the parameter name as string. If this is specified, the foreign function can be called with named parameters.

The optional third item is the default value for this parameter.

此范例演示如何包裹 Windows MessageBoxW function so that it supports default parameters and named arguments. The C declaration from the windows header file is this:

WINUSERAPI int WINAPI
MessageBoxW(
    HWND hWnd,
    LPCWSTR lpText,
    LPCWSTR lpCaption,
    UINT uType);
									

这时被包裹采用 ctypes :

>>> from ctypes import c_int, WINFUNCTYPE, windll
>>> from ctypes.wintypes import HWND, LPCWSTR, UINT
>>> prototype = WINFUNCTYPE(c_int, HWND, LPCWSTR, LPCWSTR, UINT)
>>> paramflags = (1, "hwnd", 0), (1, "text", "Hi"), (1, "caption", "Hello from ctypes"), (1, "flags", 0)
>>> MessageBox = prototype(("MessageBoxW", windll.user32), paramflags)
									

MessageBox 外来函数现在可以被调用，采用这些办法：

>>> MessageBox()
>>> MessageBox(text="Spam, spam, spam")
>>> MessageBox(flags=2, text="foo bar")
									

第 2 个范例演示输出参数。win32 GetWindowRect function retrieves the dimensions of a specified window by copying them into RECT structure that the caller has to supply. Here is the C declaration:

WINUSERAPI BOOL WINAPI
GetWindowRect(
     HWND hWnd,
     LPRECT lpRect);
									

这时被包裹采用 ctypes :

>>> from ctypes import POINTER, WINFUNCTYPE, windll, WinError
>>> from ctypes.wintypes import BOOL, HWND, RECT
>>> prototype = WINFUNCTYPE(BOOL, HWND, POINTER(RECT))
>>> paramflags = (1, "hwnd"), (2, "lprect")
>>> GetWindowRect = prototype(("GetWindowRect", windll.user32), paramflags)
>>>
									

Functions with output parameters will automatically return the output parameter value if there is a single one, or a tuple containing the output parameter values when there are more than one, so the GetWindowRect function now returns a RECT instance, when called.

Output parameters can be combined with the errcheck protocol to do further output processing and error checking. The win32 GetWindowRect api function returns a BOOL to signal success or failure, so this function could do the error checking, and raises an exception when the api call failed:

>>> def errcheck(result, func, args):
...     if not result:
...         raise WinError()
...     return args
...
>>> GetWindowRect.errcheck = errcheck
>>>
									

若 errcheck function returns the argument tuple it receives unchanged, ctypes continues the normal processing it does on the output parameters. If you want to return a tuple of window coordinates instead of a RECT instance, you can retrieve the fields in the function and return them instead, the normal processing will no longer take place:

>>> def errcheck(result, func, args):
...     if not result:
...         raise WinError()
...     rc = args[1]
...     return rc.left, rc.top, rc.bottom, rc.right
...
>>> GetWindowRect.errcheck = errcheck
>>>
									

16.16.2.5. 实用函数 ¶

ctypes. addressof ( obj ) ¶

以整数形式返回内存缓冲的地址。 obj 必须是 ctypes 类型的实例。

ctypes. alignment ( obj_or_type ) ¶

返回 ctypes 类型的对齐要求。 obj_or_type 必须是 ctypes 类型或实例。

ctypes. byref ( obj [ , offset ] ) ¶

返回轻量指针，指向 obj , which must be an instance of a ctypes type. offset defaults to zero, and must be an integer that will be added to the internal pointer value.

byref(obj, offset) corresponds to this C code:

(((char *)&obj) + offset)
											

The returned object can only be used as a foreign function call parameter. It behaves similar to pointer(obj) , but the construction is a lot faster.

ctypes. cast ( obj , type ) ¶

This function is similar to the cast operator in C. It returns a new instance of type 其指向同一内存块如 obj . type 必须是指针类型，且 obj 必须是可以被解释为指针的对象。

ctypes. create_string_buffer ( init_or_size , size=None ) ¶

This function creates a mutable character buffer. The returned object is a ctypes array of c_char .

init_or_size must be an integer which specifies the size of the array, or a bytes object which will be used to initialize the array items.

If a bytes object is specified as first argument, the buffer is made one item larger than its length so that the last element in the array is a NUL termination character. An integer can be passed as second argument which allows specifying the size of the array if the length of the bytes should not be used.

ctypes. create_unicode_buffer ( init_or_size , size=None ) ¶

This function creates a mutable unicode character buffer. The returned object is a ctypes array of c_wchar .

init_or_size must be an integer which specifies the size of the array, or a string which will be used to initialize the array items.

If a string is specified as first argument, the buffer is made one item larger than the length of the string so that the last element in the array is a NUL termination character. An integer can be passed as second argument which allows specifying the size of the array if the length of the string should not be used.

ctypes. DllCanUnloadNow ( ) ¶

Windows only: This function is a hook which allows implementing in-process COM servers with ctypes. It is called from the DllCanUnloadNow function that the _ctypes extension dll exports.

ctypes. DllGetClassObject ( ) ¶

Windows only: This function is a hook which allows implementing in-process COM servers with ctypes. It is called from the DllGetClassObject function that the _ctypes extension dll exports.

ctypes.util. find_library ( name ) ¶

Try to find a library and return a pathname. name is the library name without any prefix like lib , suffix like .so , .dylib or version number (this is the form used for the posix linker option -l ). If no library can be found, returns None .

确切功能从属系统。

ctypes.util. find_msvcrt ( ) ¶

Windows only: return the filename of the VC runtime library used by Python, and by the extension modules. If the name of the library cannot be determined, None 被返回。

If you need to free memory, for example, allocated by an extension module with a call to the free(void *) , it is important that you use the function in the same library that allocated the memory.

ctypes. FormatError ( [ code ] ) ¶

Windows only: Returns a textual description of the error code code . If no error code is specified, the last error code is used by calling the Windows api function GetLastError.

ctypes. GetLastError ( ) ¶

Windows only: Returns the last error code set by Windows in the calling thread. This function calls the Windows GetLastError() function directly, it does not return the ctypes-private copy of the error code.

ctypes. get_errno ( ) ¶

Returns the current value of the ctypes-private copy of the system errno variable in the calling thread.

ctypes. get_last_error ( ) ¶

Windows only: returns the current value of the ctypes-private copy of the system LastError variable in the calling thread.

ctypes. memmove ( dst , src , count ) ¶

Same as the standard C memmove library function: copies count 字节来自 src to dst . dst and src must be integers or ctypes instances that can be converted to pointers.

ctypes. memset ( dst , c , count ) ¶

Same as the standard C memset library function: fills the memory block at address dst with count bytes of value c . dst must be an integer specifying an address, or a ctypes instance.

ctypes. POINTER ( type ) ¶

This factory function creates and returns a new ctypes pointer type. Pointer types are cached and reused internally, so calling this function repeatedly is cheap. type 必须是 ctypes 类型。

ctypes. pointer ( obj ) ¶

This function creates a new pointer instance, pointing to obj . The returned object is of the type POINTER(type(obj)) .

Note: If you just want to pass a pointer to an object to a foreign function call, you should use byref(obj) which is much faster.

ctypes. resize ( obj , size ) ¶

This function resizes the internal memory buffer of obj , which must be an instance of a ctypes type. It is not possible to make the buffer smaller than the native size of the objects type, as given by sizeof(type(obj)) , but it is possible to enlarge the buffer.

ctypes. set_errno ( value ) ¶

Set the current value of the ctypes-private copy of the system errno variable in the calling thread to value and return the previous value.

ctypes. set_last_error ( value ) ¶

Windows only: set the current value of the ctypes-private copy of the system LastError variable in the calling thread to value and return the previous value.

ctypes. sizeof ( obj_or_type ) ¶

Returns the size in bytes of a ctypes type or instance memory buffer. Does the same as the C sizeof operator.

ctypes. string_at ( address , size=-1 ) ¶

This function returns the C string starting at memory address address as a bytes object. If size is specified, it is used as size, otherwise the string is assumed to be zero-terminated.

ctypes. WinError ( code=None , descr=None ) ¶

Windows only: this function is probably the worst-named thing in ctypes. It creates an instance of OSError. If code is not specified, GetLastError is called to determine the error code. If descr is not specified, FormatError() is called to get a textual description of the error.

3.3 版改变： An instance of WindowsError used to be created.

ctypes. wstring_at ( address , size=-1 ) ¶

This function returns the wide character string starting at memory address address as a string. If size is specified, it is used as the number of characters of the string, otherwise the string is assumed to be zero-terminated.

16.16.2.6. 数据类型 ¶

class ctypes. _CData ¶

This non-public class is the common base class of all ctypes data types. Among other things, all ctypes type instances contain a memory block that hold C compatible data; the address of the memory block is returned by the addressof() helper function. Another instance variable is exposed as _objects ; this contains other Python objects that need to be kept alive in case the memory block contains pointers.

Common methods of ctypes data types, these are all class methods (to be exact, they are methods of the metaclass ):

from_buffer ( source [ , offset ] ) ¶

This method returns a ctypes instance that shares the buffer of the source object. The source object must support the writeable buffer interface. The optional offset parameter specifies an offset into the source buffer in bytes; the default is zero. If the source buffer is not large enough a ValueError 被引发。

from_buffer_copy ( source [ , offset ] ) ¶

This method creates a ctypes instance, copying the buffer from the source object buffer which must be readable. The optional offset parameter specifies an offset into the source buffer in bytes; the default is zero. If the source buffer is not large enough a ValueError 被引发。

from_address ( address ) ¶

This method returns a ctypes type instance using the memory specified by address which must be an integer.

from_param ( obj ) ¶

This method adapts obj to a ctypes type. It is called with the actual object used in a foreign function call when the type is present in the foreign function’s argtypes tuple; it must return an object that can be used as a function call parameter.

All ctypes data types have a default implementation of this classmethod that normally returns obj if that is an instance of the type. Some types accept other objects as well.

in_dll ( library , name ) ¶

This method returns a ctypes type instance exported by a shared library. name is the name of the symbol that exports the data, library is the loaded shared library.

Common instance variables of ctypes data types:

_b_base_ ¶

Sometimes ctypes data instances do not own the memory block they contain, instead they share part of the memory block of a base object. The _b_base_ read-only member is the root ctypes object that owns the memory block.

_b_needsfree_ ¶

This read-only variable is true when the ctypes data instance has allocated the memory block itself, false otherwise.

_objects ¶

This member is either None or a dictionary containing Python objects that need to be kept alive so that the memory block contents is kept valid. This object is only exposed for debugging; never modify the contents of this dictionary.

16.16.2.7. 基础数据类型 ¶

class ctypes. _SimpleCData ¶

This non-public class is the base class of all fundamental ctypes data types. It is mentioned here because it contains the common attributes of the fundamental ctypes data types. _SimpleCData 是子类对于 _CData , so it inherits their methods and attributes. ctypes data types that are not and do not contain pointers can now be pickled.

Instances have a single attribute:

value ¶

This attribute contains the actual value of the instance. For integer and pointer types, it is an integer, for character types, it is a single character bytes object or string, for character pointer types it is a Python bytes object or string.

当 value attribute is retrieved from a ctypes instance, usually a new object is returned each time. ctypes does not implement original object return, always a new object is constructed. The same is true for all other ctypes object instances.

Fundamental data types, when returned as foreign function call results, or, for example, by retrieving structure field members or array items, are transparently converted to native Python types. In other words, if a foreign function has a restype of c_char_p , you will always receive a Python bytes object, not a c_char_p 实例。

Subclasses of fundamental data types do not inherit this behavior. So, if a foreign functions restype 是子类对于 c_void_p , you will receive an instance of this subclass from the function call. Of course, you can get the value of the pointer by accessing the value 属性。

这些是基础 ctypes 数据类型：

class ctypes. c_byte ¶

表示 C signed char datatype, and interprets the value as small integer. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_char ¶

表示 C char datatype, and interprets the value as a single character. The constructor accepts an optional string initializer, the length of the string must be exactly one character.

class ctypes. c_char_p ¶

表示 C char * datatype when it points to a zero-terminated string. For a general character pointer that may also point to binary data, POINTER(c_char) must be used. The constructor accepts an integer address, or a bytes object.

class ctypes. c_double ¶

表示 C double 数据类型。构造函数接受可选浮点初始化程序。

class ctypes. c_longdouble ¶

表示 C long double datatype. The constructor accepts an optional float initializer. On platforms where sizeof(long double) == sizeof(double) ，它是别名 c_double .

class ctypes. c_float ¶

表示 C float 数据类型。构造函数接受可选浮点初始化程序。

class ctypes. c_int ¶

表示 C signed int datatype. The constructor accepts an optional integer initializer; no overflow checking is done. On platforms where sizeof(int) == sizeof(long) ，它是别名 c_long .

class ctypes. c_int8 ¶

表示 C 8-bit signed int 数据类型。通常别名为 c_byte .

class ctypes. c_int16 ¶

表示 C 16-bit signed int 数据类型。通常别名为 c_short .

class ctypes. c_int32 ¶

表示 C 32-bit signed int 数据类型。通常别名为 c_int .

class ctypes. c_int64 ¶

表示 C 64-bit signed int 数据类型。通常别名为 c_longlong .

class ctypes. c_long ¶

表示 C signed long datatype. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_longlong ¶

表示 C signed long long datatype. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_short ¶

表示 C signed short datatype. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_size_t ¶

表示 C size_t 数据类型。

class ctypes. c_ssize_t ¶

表示 C ssize_t 数据类型。

3.2 版新增。

class ctypes. c_ubyte ¶

表示 C unsigned char datatype, it interprets the value as small integer. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_uint ¶

表示 C unsigned int datatype. The constructor accepts an optional integer initializer; no overflow checking is done. On platforms where sizeof(int) == sizeof(long) it is an alias for c_ulong .

class ctypes. c_uint8 ¶

表示 C 8-bit unsigned int 数据类型。通常别名为 c_ubyte .

class ctypes. c_uint16 ¶

表示 C 16-bit unsigned int 数据类型。通常别名为 c_ushort .

class ctypes. c_uint32 ¶

表示 C 32-bit unsigned int 数据类型。通常别名为 c_uint .

class ctypes. c_uint64 ¶

表示 C 64-bit unsigned int 数据类型。通常别名为 c_ulonglong .

class ctypes. c_ulong ¶

表示 C unsigned long datatype. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_ulonglong ¶

表示 C unsigned long long datatype. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_ushort ¶

表示 C unsigned short datatype. The constructor accepts an optional integer initializer; no overflow checking is done.

class ctypes. c_void_p ¶

表示 C void * type. The value is represented as integer. The constructor accepts an optional integer initializer.

class ctypes. c_wchar ¶

表示 C wchar_t datatype, and interprets the value as a single character unicode string. The constructor accepts an optional string initializer, the length of the string must be exactly one character.

class ctypes. c_wchar_p ¶

表示 C wchar_t * datatype, which must be a pointer to a zero-terminated wide character string. The constructor accepts an integer address, or a string.

class ctypes. c_bool ¶

Represent the C bool datatype (more accurately, _Bool from C99). Its value can be True or False , and the constructor accepts any object that has a truth value.

class ctypes. HRESULT ¶

Windows only: Represents a HRESULT value, which contains success or error information for a function or method call.

class ctypes. py_object ¶

表示 C PyObject * datatype. Calling this without an argument creates a NULL PyObject * pointer.

ctypes.wintypes module provides quite some other Windows specific data types, for example HWND , WPARAM ，或 DWORD . Some useful structures like MSG or RECT are also defined.

16.16.2.8. 结构化数据类型 ¶

class ctypes. Union ( *args , **kw ) ¶

采用本机字节序用于 Union 的抽象基类。

class ctypes. BigEndianStructure ( *args , **kw ) ¶

用于 Structure 的抽象基类，采用 big endian 字节序。

class ctypes. LittleEndianStructure ( *args , **kw ) ¶

用于 Structure 的抽象基类，采用 little endian 字节序。

Structures with non-native byte order cannot contain pointer type fields, or any other data types containing pointer type fields.

class ctypes. Structure ( *args , **kw ) ¶

用于 Structure 的抽象基类，采用 native 字节序。

Concrete structure and union types must be created by subclassing one of these types, and at least define a _fields_ class variable. ctypes will create descriptor s which allow reading and writing the fields by direct attribute accesses. These are the

_fields_ ¶

A sequence defining the structure fields. The items must be 2-tuples or 3-tuples. The first item is the name of the field, the second item specifies the type of the field; it can be any ctypes data type.

For integer type fields like c_int , a third optional item can be given. It must be a small positive integer defining the bit width of the field.

Field names must be unique within one structure or union. This is not checked, only one field can be accessed when names are repeated.

It is possible to define the _fields_ 类变量 after the class statement that defines the Structure subclass, this allows creating data types that directly or indirectly reference themselves:

class List(Structure):
    pass
List._fields_ = [("pnext", POINTER(List)),
                 ...
                ]
													

_fields_ class variable must, however, be defined before the type is first used (an instance is created, sizeof() is called on it, and so on). Later assignments to the _fields_ class variable will raise an AttributeError.

It is possible to defined sub-subclasses of structure types, they inherit the fields of the base class plus the _fields_ defined in the sub-subclass, if any.

_pack_ ¶

An optional small integer that allows overriding the alignment of structure fields in the instance. _pack_ must already be defined when _fields_ is assigned, otherwise it will have no effect.

_anonymous_ ¶

An optional sequence that lists the names of unnamed (anonymous) fields. _anonymous_ must be already defined when _fields_ is assigned, otherwise it will have no effect.

The fields listed in this variable must be structure or union type fields. ctypes will create descriptors in the structure type that allows accessing the nested fields directly, without the need to create the structure or union field.

Here is an example type (Windows):

class _U(Union):
    _fields_ = [("lptdesc", POINTER(TYPEDESC)),
                ("lpadesc", POINTER(ARRAYDESC)),
                ("hreftype", HREFTYPE)]
class TYPEDESC(Structure):
    _anonymous_ = ("u",)
    _fields_ = [("u", _U),
                ("vt", VARTYPE)]
													

TYPEDESC structure describes a COM data type, the vt field specifies which one of the union fields is valid. Since the u field is defined as anonymous field, it is now possible to access the members directly off the TYPEDESC instance. td.lptdesc and td.u.lptdesc are equivalent, but the former is faster since it does not need to create a temporary union instance:

td = TYPEDESC()
td.vt = VT_PTR
td.lptdesc = POINTER(some_type)
td.u.lptdesc = POINTER(some_type)
													

It is possible to defined sub-subclasses of structures, they inherit the fields of the base class. If the subclass definition has a separate _fields_ variable, the fields specified in this are appended to the fields of the base class.

Structure and union constructors accept both positional and keyword arguments. Positional arguments are used to initialize member fields in the same order as they are appear in _fields_ . Keyword arguments in the constructor are interpreted as attribute assignments, so they will initialize _fields_ with the same name, or create new attributes for names not present in _fields_ .

16.16.2.9. 数组和指针 ¶

class ctypes. Array ( *args ) ¶

用于数组的抽象基类。

The recommended way to create concrete array types is by multiplying any ctypes data type with a positive integer. Alternatively, you can subclass this type and define _length_ and _type_ class variables. Array elements can be read and written using standard subscript and slice accesses; for slice reads, the resulting object is not itself an Array .

_length_ ¶

A positive integer specifying the number of elements in the array. Out-of-range subscripts result in an IndexError . Will be returned by len() .

_type_ ¶

Specifies the type of each element in the array.

Array subclass constructors accept positional arguments, used to initialize the elements in order.

class ctypes. _Pointer ¶

用于指针的私有，抽象基类。

Concrete pointer types are created by calling POINTER() with the type that will be pointed to; this is done automatically by pointer() .

If a pointer points to an array, its elements can be read and written using standard subscript and slice accesses. Pointer objects have no size, so len() 会引发 TypeError . Negative subscripts will read from the memory before the pointer (as in C), and out-of-range subscripts will probably crash with an access violation (if you’re lucky).

_type_ ¶

指定指向的类型。

contents ¶

Returns the object to which to pointer points. Assigning to this attribute changes the pointer to point to the assigned object.