Python Ctypes 結構體指針處理(函數參數，函數返回)

C函數需要傳遞結構體指針是常事，但是和Python交互就有點麻煩事了，經過研究也可以了。

<結構體指針作為函數參數>

來看下C測試例子:

1. #include <stdio.h>
2. typedef struct StructPointerTest* StructPointer;
3. struct StructPointerTest{
4. int x;
5. int y;
6. };
7. void test(StructPointer p) {
8. p->x = 101;
9. p->y = 201;
10. }

這裡test裡面需要傳入結構體指針,函數中的實現很簡單，就是改變x 和 y 的值這個函數將被python調用。

使用Python調用時，需要模擬申明個結構體(class):

1. from ctypes import *
2. class StructPointerTest(Structure):
3. _fields_ =[('x', c_int),
4. ('y', c_int)]

Usage:

1. ##Structure Pointer Operation
2. SPTobj = pointer(StructPointerTest(1, 2))
3. print SPTobj
4. print SPTobj.contents.x
5. print SPTobj.contents.y

<函數返回結構體指針>

C函數測試例子改成如下:

1. StructPointer test() {
2. StructPointer p = (StructPointer)malloc(sizeof(struct StructPointerTest));
3. p->x = 101;
4. p->y = 201;
5. return p;
6. }

Python程序處理如下:

1. from ctypes import *
2. class StructPointer(Structure):
3. pass
5. StructPointer._fields_=[('x', c_int),
6. ('y', c_int),
7. ('next', POINTER(StructPointer))]
10. lib = cdll.LoadLibrary('./StructPointer.so')
11. lib.test.restype = POINTER(StructPointer)
13. p = lib.test()
14. print p.contents.x

關於resttype可以參見 Tutorial : By default functions are assumed to return the C int type. Other return types can be specified by setting the restype attribute of the function object.