![](/img/trans.png)
[英]How to send data from Python script to JavaScript and vice-versa?
[英]How to return a class object from c++ (DllExport) to python using ctypes vice-versa?
我在c ++中有一个函数,它将类对象返回到python,我在python(ctypes import)中有一个包装器在下面的代码片段中,当我从python调用函数(Get_Student)时,学校有用c ++创建的新实例,我无法检索学生班的数据,
// c ++代码是:
#include"stdafx.h"
#include<string>
using namespace std;
class Student
{
int ID;
public:
void SetId(int id)
{
ID = id;
}
int GetId()
{
return ID;
}
};
class School{
Student* stud;
public:
void* CreateStudent()
{
stud = new Student();
return stud;
}
Student* GetStudent()
{
return stud;
}
};
extern "C"
{
__declspec(dllexport) void Student_SetId(Student* stud ,int id)
{
stud->SetId(id);
}
__declspec(dllexport) int Student_GetId(Student* stud)
{
return (stud->GetId());
}
__declspec(dllexport) School* School_new(){
return new School();
}
__declspec(dllexport) void* School_CreateStudent(School* school){
return (school->CreateStudent());
}
__declspec(dllexport)Student* School_GetStudent(School* school){
return (school->GetStudent());
}
}
#The Python code is:
from ctypes import*
mydll=cdll.LoadLibrary("D:\\shameel\\Cpp\\Sample_class\\Debug\\Sample_class.dll")
class Student():
def __init__(self):
self.nativeStudent = mydll.School_CreateStudent()
def Set_Id(self,arg):
mydll.Student_SetId(self.nativeStudent,arg)
def Get_Id(self):
return (mydll.Student_GetId(self.nativeStudent))
class School():
def __init__(self):
self.nativeSchool = mydll.School_new()
def CreateStudent(self):
return Student()
def Get_Student(self):
mydll.School_GetStudent.restype = c_void_p
self.nativestd = mydll.School_GetStudent(self.nativeSchool)
return (self.nativestd)
#The Python call is as follows:
fobj = School()
std_new = fobj.CreateStudent()
std_new.Set_Id(3)
Id = std_new.Get_Id()
getobj =fobj.Get_Student()
print(getobj)
当我打印getobj时,它的输出是“无”。
我如何从CPP获得相同的对象?
除非另有说明,否则ctypes
假定参数和返回值是32位整数( ctypes.c_int
)。 特别是如果您使用64位Python,指针将被截断为32位。 首先要做的是声明函数参数并正确返回值 :
mydll.Student_SetId.argtypes = c_void_p,c_int
mydll.Student_SetId.restype = None
mydll.Student_GetId.argtypes = c_void_p,
mydll.Student_GetId.restype = c_int
mydll.School_new.argtypes = ()
mydll.School_new.restype = c_void_p
mydll.School_CreateStudent.argtypes = c_void_p,
mydll.School_CreateStudent.restype = c_void_p
mydll.School_GetStudent.argtypes = c_void_p,
mydll.School_GetStudent.restype = c_void_p
这也可以帮助您捕获错误,例如School_CreateStudent()
需要通过School*
才能正常工作。
要捕获更多错误,请声明特定的指针类型。 这是一个将显示其类型和示例的小类:
class Ptr(c_void_p):
def __repr__(self):
cls_name = self.__class__.__name__
if self.value is not None:
return f'{cls_name}({self.value:#x})'
return f'{cls_name}(None)'
class pStudent(Ptr): pass
class pSchool(Ptr): pass
演示:
>>> p = pSchool()
>>> p
pSchool(None)
然后声明函数参数和结果如下:
mydll.Student_SetId.argtypes = pStudent,c_int
mydll.Student_SetId.restype = None
mydll.Student_GetId.argtypes = pStudent,
mydll.Student_GetId.restype = c_int
mydll.School_new.argtypes = ()
mydll.School_new.restype = pSchool
mydll.School_CreateStudent.argtypes = pSchool,
mydll.School_CreateStudent.restype = pStudent
mydll.School_GetStudent.argtypes = pSchool,
mydll.School_GetStudent.restype = pStudent
现在,在Python中错误地使用代码的任何地方都应该给你一个很好的错误信息。
修复C ++和Python代码后, print(getobj)
输出将如下所示:
pStudent(0x1b54b89b350)
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.