使用Cype调用带有Python参数的C++方法导致“不知道如何转换参数”错误

Tom Spargo • 3 年前 • 1387 次点击

我试图从Python 3使用下面的C++类。7,但无法让第一个方法“设置”工作,更不用说运算符重载方法了。我尝试了Python包装器和extern块的许多变体,但我要么遇到了“不知道如何转换参数5”错误,要么遇到了分段错误。网上的例子和我找到的答案都太基本了,或者是解决了其他问题。

我的argtypes第一个参数应该是指向对象的指针吗?我不知道用什么语法来表示。

CMatrix。h:

#include <stdio.h>

class CMatrix
{
public:
    CMatrix(int d1);
    CMatrix(int d1, int d2);
    CMatrix(int d1, int d2, int d3);
    CMatrix (float f1, float f2, float f3);
    ~CMatrix();
    
    void Set(int x, int y, int z, float f);
    void operator=(const float f);
    CMatrix& operator=(const CMatrix &cm);
    inline float& operator()(const int i) {
        return m[i];}
    inline float& operator()(const int i, const int j) {
        return m[i*s2+j];}
    inline float& operator()(const int i, const int j, const int k) {
        return m[i*s23+j*s3+k];}
    int s1, s2, s3;     // dimensions of array
    int s23;            // s2*s3;
    float *m;           // pointer to first element of matrix.
    int dimensions;     // 1, 2, or 3.
};

extern "C" {
    CMatrix* CMatrix_new1(int i) {return new CMatrix(i); }
    CMatrix* CMatrix_new2(int i, int j) {return new CMatrix(i, j); }
    CMatrix* CMatrix_new3(int i, int j, int k) {return new CMatrix(i, j, k); }
    void CMatrix_Set(CMatrix* cm, int x, int y, int z, float f) {cm->Set(x, y, z, f); }
}

cmWrapper。py:

import ctypes as c
lib = c.cdll.LoadLibrary('./libCMatrix.o')
lib.CMatrix_Set.argtypes = [c.c_int, c.c_int, c.c_int, c.c_float]

class CMatrix(object):
    def __init__(self, i, j, k):
        if j==0 and k==0:
            self.obj = lib.CMatrix_new1(i)
        elif k==0:
            self.obj = lib.CMatrix_new2(i, j)
        else:
            self.obj = lib.CMatrix_new3(i, j, k)

    def Set(self, x, y, z, f):
        lib.CMatrix_Set(self.obj, x, y, z, f)

cm = CMatrix(2, 3, 0)
cm.Set(1, 2, 0, 99.0)

追溯:

>>> import cmWrapper
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/.../ctypes/cmWrapper.py", line 18, in <module>
    cm.Set(1, 2, 0, 99.0)
  File "/.../ctypes/cmWrapper.py", line 15, in Set
    lib.CMatrix_Set(self.obj, x, y, z, f)
ctypes.ArgumentError: argument 5: <class 'TypeError'>: Don't know how to convert parameter 5

如果有问题,我用C++编译了C++代码:

g++ -c -fPIC CMatrix.cpp -o CMatrix.o
g++ -shared -Wl -o libCMatrix.o CMatrix.o

这是在运行10.15.7的Mac上。

来自lldb:

Executable module set to "/Library/Frameworks/Python.framework/Versions/3.7/Resources/Python.app/Contents/MacOS/Python".
Architecture set to: x86_64h-apple-macosx-.
(lldb) 
There is a running process, detach from it and attach?: [Y/n] n
(lldb) thread list
Process 57460 stopped
* thread #1: tid = 0x47364c, 0x00007fff202f5656 libsystem_kernel.dylib`__select + 10, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
(lldb) thread continue
Resuming thread 0x47364c in process 57460
Process 57460 resuming
Process 57460 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x13835f20)
    frame #0: 0x00000001015f19b2 libCMatrix.o`CMatrix::Set(int, int, int, float) + 34
libCMatrix.o`CMatrix::Set:
->  0x1015f19b2 <+34>: movl   (%rax), %esi
    0x1015f19b4 <+36>: movl   0x4(%rax), %edx
    0x1015f19b7 <+39>: movl   0x8(%rax), %ecx
    0x1015f19ba <+42>: movl   0xc(%rax), %r8d
Target 0: (Python) stopped.

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文章 [ 2 ] | 最新文章 3 年前

• 1 楼

Joseph Sible-Reinstate Monica 3 年前

问题是:

lib.CMatrix_Set.argtypes = [c.c_int, c.c_int, c.c_int, c.c_float]

你忘了那本书的词条了 self.obj 论点将其更改为:

lib.CMatrix_Set.argtypes = [c.c_void_p, c.c_int, c.c_int, c.c_int, c.c_float]

此外,您可能应该将其设置为 restype 调用的其他函数,以便在 int 窄于 void * .

另一个选项是创建一个从 ctypes.Structure 对应于C++类,然后使用一个指针作为类型,但是之后你必须非常小心C++代码,或者布局可能会不同于C,Python所期望的。

• 2 楼

Mark Tolonen 3 年前

你必须完全匹配论点。设定 .argtypes 和 .restype 你使用的每一个函数 ctypes 可以正确地将参数封送到C并再次封送回来。如果你不设定 .重新键入 ctypes 假设返回值为 c_int (通常是有符号的32位整数)而不是(可能是64位)指针。

下面是一个有效的例子。我并没有充实每个函数,因为一个函数应该足够了。在32位和64位Python上进行了测试。

测验cpp(使用MS编译器cl/LD/EHsc/W4 test.cpp构建):

#include <stdio.h>

// Needed to export functions on Windows
#ifdef _WIN32
#   define API __declspec(dllexport)
#else
#   define API
#endif

class CMatrix
{
public:
    CMatrix(int d1) : s1(d1) { m = new float[d1]; }
    ~CMatrix() { delete [] m; }
    const float* Get(int& s) { s = s1; return m; }
    void Set(int x, float f) { m[x] = f; }
    int s1;
    float *m;
};

extern "C" {
    API CMatrix* CMatrix_new(int i) {return new CMatrix(i); }
    API const float* CMatrix_Get(CMatrix* cm, int& x) { return cm->Get(x); }
    API void CMatrix_Set(CMatrix* cm, int x, float f) { cm->Set(x, f); }
    API void CMatrix_delete(CMatrix* cm) { delete cm; }
}

测验py

import ctypes as ct

# For type checking the returned pointer.
class _CMatrix(ct.c_void_p) : pass
PCMatrix = ct.POINTER(_CMatrix)

class CMatrix:

    _dll = ct.CDLL('./test')
    _dll.CMatrix_new.argtypes = ct.c_int, 
    _dll.CMatrix_new.restype = PCMatrix
    _dll.CMatrix_Get.argtypes = PCMatrix, ct.POINTER(ct.c_int)
    _dll.CMatrix_Get.restype = ct.POINTER(ct.c_float)
    _dll.CMatrix_Set.argtypes = PCMatrix, ct.c_int, ct.c_float
    _dll.CMatrix_Set.restype = None
    _dll.CMatrix_delete.argtypes = PCMatrix, 
    _dll.CMatrix_delete.restype = None

    def __init__(self, i):
        self.obj = self._dll.CMatrix_new(i)

    def Set(self, x, f):
        self._dll.CMatrix_Set(self.obj, x, f)

    def Get(self):
        size = ct.c_int()
        m = self._dll.CMatrix_Get(self.obj, ct.byref(size))
        return m[:size.value]

    def __del__(self):
        self._dll.CMatrix_delete(self.obj)

cm = CMatrix(2)
cm.Set(0, 1.5)
cm.Set(1, 2.5)
print(cm.Get())

输出:

[1.5, 2.5]

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