python - 返回指向具有 ctypes 的结构的指针的函数

Question

我的C函数原型(prototype)是:

typedef struct {
    int a; 
    int b;
} foo_t;

foo_t* foo(int a);

在 Python 中我必须重新定义我的结构:

class Foo(Structure):
    _fields_ = [("a", c_int), ("b", c_int)]

我的问题是如何在 Foo 中正确地转换我的返回值？

>>> dll.foo.restype = POINTER(Foo)
>>> ret = dll.foo(42);
>>> print ret
<dll.LP_Foo object at 0xffe7c98c>
>>> print ret.a
AttributeError: 'LP_Foo' object has no attribute 'a'

我也尝试过 Foo 而不是 POINTER(Foo)。有了这个，我可以访问 Foo 成员，但值是错误的。

来自 ctypes我可以读到这个:

ctypes.POINTER(type) This factory function creates and returns a new ctypes pointer type. Pointer types are cached an reused internally, so calling this function repeatedly is cheap. type must be a ctypes type

所以类型不能是Foo。我可能必须找到另一种方法。

Answer 1

来自文档:

Pointer instances have a contents attribute which returns the object to which the pointer points

所以尝试:

>>> print ret.contents.a

请注意文档说明:

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