[英]Returning pointer on vector of pointers from C++ dll to Python
我已成功將指向指針的指針(包含wchar_t*
)從c ++ dll返回到Python,如下所示:C ++代碼:
...
typedef struct myStruct{
wchar_t* id;
wchar_t* content;
wchar_t* message;
} myStruct;
DLLAPI myStruct* DLLApiGetStruct(){
myStruct* testStruct = new myStruct();
testStruct->id = _T("some id");
testStruct->content = _T("some content");
testStruct->message = _T("some message");
return testStruct;
}
Python代碼:
class MyPyStruct(Structure):
_fields_ = [
("id", c_wchar_p),
("content", c_wchar_p),
("message", c_wchar_p)
]
...
...
myDLL = cdll.LoadLibrary('myDLL.dll')
myDLL.DLLApiGetStruct.restype = POINTER(MyPyStruct)
result = myDLL.DLLApiGetStruct().contents
print result.id, result.content, result. message# those are valid values
好的,這很好, 問題是現在我需要在指向這些結構的指針的向量上返回指針。 我已經試過了:
C ++代碼:
typedef std::vector<myStruct*> myVector;
...
DLLAPI myVector* DLLApiGetVector(){
myVector* testVektor = new myVector();
for(i=0; i< 5; i++){
myStruct* testStruct = new myStruct();
testStruct->id = _T("some id");
testStruct->content = _T("some content");
testStruct->message = _T("some message");
testVektor->push_back(testStruct);
}
return testVektor;// all values in it are valid
}
Python代碼:
#我認為第一行和第二行不正確(這是進行restype的正確方法嗎?):
vectorOfPointersType = (POINTER(DeltaDataStruct) * 5) #5 is number of structures in vector
myDLL.DLLApiGetVector.restype = POINTER(vectorOfPointersType)
vectorOfPointersOnMyStruct= myDLL.DLLApiGetVector.contents
for pointerOnMyStruct in vectorOfPointersOnMyStruct:
result = pointerOnMyStruct.contents
print result.id, result.content, result.message
最后一行中的值無效-我猜這是內存中的一些隨機部分。 這是我得到的錯誤:
UnicodeEncodeError: 'charmap' codec can't encode characters in position 0-11: character maps to <undefined>
vector
與C兼容,但是您需要將第一個元素的地址傳遞給C調用者(或ctypes)。 就是說,您必須保持指向vector
的指針,以便稍后釋放它。 我認為從一開始就使用數組會更好。 您可以將int
out參數傳遞給函數,以接收數組的長度。 由於您使用new
進行分配,因此請記住,如果分配失敗,則會捕獲bad_alloc
異常。
就個人而言,我將使用結構數組而不是指針數組,以使數據位於單個連續的塊中。 這會在ctypes中產生更清晰的界面。 使用指針數組,您必須取消引用兩次才能獲取該結構。
C ++:
#include <new>
#include <cwchar>
typedef struct myStruct {
wchar_t *id;
wchar_t *content;
wchar_t *message;
} myStruct;
const wchar_t ID[] = L"some id";
const wchar_t CONTENT[] = L"some content";
const wchar_t MESSAGE[] = L"some message";
DLLAPI myStruct **DLLApiGetArray(int *size)
{
int i, n = 5;
myStruct **result;
try {
result = new myStruct *[n];
for(i = 0; i < n; i++) {
myStruct *tmp = new myStruct();
tmp->id = new wchar_t[wcslen(ID) + 1];
tmp->content = new wchar_t[wcslen(CONTENT) + 1];
tmp->message = new wchar_t[wcslen(MESSAGE) + 1];
wcscpy(tmp->id, ID);
wcscpy(tmp->content, CONTENT);
wcscpy(tmp->message, MESSAGE);
result[i] = tmp;
}
} catch (std::bad_alloc &ba) {
*size = -1; return NULL;
}
*size = n; return result;
}
蟒蛇:
from ctypes import *
class myStruct(Structure):
_fields_ = [
("id", c_wchar_p),
("content", c_wchar_p),
("message", c_wchar_p)
]
myDLL = cdll.myDLL
myDLL.DLLApiGetArray.restype = POINTER(POINTER(myStruct))
myDLL.DLLApiGetArray.argtypes = [POINTER(c_int)]
n = c_int()
p = myDLL.DLLApiGetArray(byref(n))
n = n.value
遍歷結果的示例:
>>> for i in range(n):
... print i, p[i][0].id
...
0 some id
1 some id
2 some id
3 some id
4 some id
僅供參考,將_T
宏與顯式wchar_t
數組一起使用是不正確的。 這適用於Microsoft的TCHAR
類型,可編譯為ANSI vs Unicode。 使用L"wide character string literals"
。
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