[英]Python Ctypes read char* returned from C++ dll
I am discovering the world of ctypes because I am writing a DLL in C++ on Windows with a C wrapper to be able to use it on Python for example.我正在探索 ctypes 的世界,因为我正在 Windows 上用 C++ 编写一个带有 C 包装器的 DLL,以便能够在 Python 上使用它。 I don't understand how it works with pointer on Python when I return for example a char * from my C++ function, how to get the data at the adress of the pointer ?当我从 C++ 函数返回例如 char * 时,我不明白它如何处理 Python 上的指针,如何获取指针地址处的数据?
myClass.h
file: myClass.h
文件:
#include "myClassInc.h"
class __declspec(dllexport) myClass// __declspec to generate .lib file
{
public:
// Attributes
char * name;
// Methods
myClass();
~myClass();
bool myMethod(string);
};
myClassInc.h
(C wrapper) : myClassInc.h
(C 包装器):
#ifdef MYCLASS
# define EXPORT __declspec(dllexport)
#else
# define EXPORT __declspec(dllimport)
#endif
// Wrapper in C for others languages (LabVIEW, Python, C#, ...)
extern "C"
{
EXPORT typedef struct myClass myClass; // make the class opaque to the wrapper
EXPORT myClass* cCreateObject(void);
EXPORT char* cMyMethod(myClass* pMyClass);
}
and myClass.cpp
:和myClass.cpp
:
#include "myClass.h"
myClass::myClass() {}
myClass::~myClass() {}
bool myClass::myMethod(string filename_video)
{
int iLength = filename_video.length();
name = new char[iLength+1];
strcpy(name, filename_video.c_str());
return true;
}
myClass* cCreateObject(void)
{
return new myClass();
}
char * cMyMethod(myClass* pMyClass)
{
if (pMyClass->myMethod("hello world"))
return pMyClass->name;
}
Finally pythonScript.py
:最后pythonScript.py
:
from ctypes import *
mydll = cdll.LoadLibrary("mydll.dll")
class mydllClass(object):
def __init__(self):
mydll.cCreateObject.argtypes = [c_void_p]
mydll.cCreateObject.restype = c_void_p
mydll.cMyMethod.argtypes = [c_void_p]
mydll.cMyMethod.restype = POINTER(c_char_p)
self.obj = mydll.cCreateObject("")
def myMethod(self):
return mydll.cMyMethod(self.obj)
f = mydllClass() # Create object
a = f.myMethod() # WANT HERE TO READ "HELLO WORLD"
The result in a is <__main__.LP_c_char_p object at 0x0000000002A4A4C8>
. a 中的结果是<__main__.LP_c_char_p object at 0x0000000002A4A4C8>
。
I don't find on the ctypes documentation how to read the data of a pointer like this.我没有在 ctypes 文档中找到如何读取这样的指针数据。 Can you help me please?你能帮我吗?
The same question will follow if I want to pass from Python a char * to myDll, how to do this (typically to give at the dll the path of a file to read from Python).如果我想从 Python 传递一个 char * 到 myDll,将出现同样的问题,如何做到这一点(通常是在 dll 中提供从 Python 读取的文件路径)。
c_char_p
is a char*
. c_char_p
是一个char*
。 POINTER(c_char_p)
is a char**
. POINTER(c_char_p)
是一个char**
。 Fix your .restype
and you should be good.修复你的.restype
,你应该很好。 ctypes
has a default behavior of converting a c_char_p
to a Python byte string. ctypes
具有将c_char_p
转换为 Python 字节字符串的默认行为。
Also, mydll.cCreateObject.argtypes = None
is correct for no arguments.此外, mydll.cCreateObject.argtypes = None
对于没有参数是正确的。 The existing definition states a void*
is a required parameter.现有定义指出void*
是必需参数。
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