Access C structure from python

Question

I am to create a python script that will access a windows dll function. I was successful in accessing the dll and its functions. Now that, I have a c function as ``` FIOSCR331_API int FIOCreateDeviceInfoList (PDEVINFO pDevInfoSet) ``` the problem is the `PDEVINFO` structure. I must create a structure in python and access this structure. The C structure is as follows ``` typedef struct tagDEVINFO { char szDeviceName[MAX_PATH]; char szPCSCName[MAX_PATH]; BOOL bPassedFilter; BOOL bUpdatePassed; DWORD dwUpdateOrder; DWORD dwPnP_ID; DWORD dwFWVersion; PDEVEXTENSION pDevExtension; } DEVINFO, *PDEVINFO; ``` the C function is as follows ``` FIOSCR331_API int FIOCreateDeviceInfoList (PDEVINFO pDevInfoSet) { int nFIOStatus; do { if ( NULL == pDevInfoSet ) { printf("this is inside C code
"); nFIOStatus = IDS_GENERIC_ERROR; //(200) break; } else printf ("
%s ",pDevInfoSet->szPCSCName); }while(false); } ``` Now the Python code I implemented ``` class DEVINFO(Structure): _fields_ = [("szDeviceNam…

Accepted Answer

Your structure declaration is wrong. It should be:

```
class DEVINFO(Structure):
    _fields_ = [
        ("szDeviceName", c_char*wintypes.MAX_PATH),
        ("szPCSCName", c_char*wintypes.MAX_PATH),
        ("bPassedFilter", wintypes.BOOL),
        ("bUpdatePassed", wintypes.BOOL),
        ("dwUpdateOrder", wintypes.DWORD),
        ("dwPnp_ID", wintypes.DWORD),
        ("dwFWVersion", wintypes.DWORD),
        ("pDevExtension", POINTER(DEVEXTENSION))
    ]
```

You must also pass a pointer to the `DEVINFO` struct when you call `FIOCreateDeviceInfoList()`. I'd do it like this:

```
funcCreateList = lib.FIOCreateDeviceInfoList(byref(devInfo))
```

As @eryksun helpfully points out, adding

```
lib.FIOCreateDeviceInfoList.argtypes = [POINTER(DEVINFO)]
```

before the call to `FIOCreateDeviceInfoList()` will make `ctypes` perform runtime type checking.

Access C structure from python

Solution

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