accessing functions from a dll using python ctypes

[dilbert_here00]

Hi,

I was trying to access some functions from a dll using python ctypes, but not sure how to pass pointers to get it to work.
Here is an example of what i am trying to call:

GetAvailableDevices  ( SdkHandle  session,  
  DeviceDetail *  pDev_list,  
  uint32_t *  dev_list_size   
 )  

Parameters:
[in] session Handle to the current sdk session
[in] pDev_list A pointer to an array of DeviceDetail structures that will receive the available device list information
[in,out] dev_list_size On input the size of the pDev_list array, on output the number of items filled into the array.

I tried the following:

from ctypes import *
device_list_size = 5
device_list = []
dll = cdll.LoadLibrary("C:\Sdk.dll")
session = dll.CreateSession()
dev_list = dll.GetAvailableDevices(session, pointer(device_list), pointer(device_list_size))

When I run the above i get : *** TypeError: type must have storage info

I am new to ctypes so not sure if this is correct, I would really appreciate if you could tell me the correct way of calling the above function.
Thanks in advance for your help.

Regards

[TrustyTony]

The doc is quite long and thorough, but should be helpfull: http://python.net/crew/theller/ctypes/tutorial.html#passing-pointers-or-passing-parameters-by-reference

[dilbert_here00]

Hello pyTony,

Thank you for the document it is very informative. However, since i don't have much experience with c, c++ I am still not able to gt my script to work:
I would really appreciate if you could throw some pointers & help me in translating the following c++ code to python:

Definitions.h
typedef struct
{
    DeviceTechType            eTechnology;              
    DeviceFormFactorType      eFormFactor;               
    char                      szDescription[NW_MAX_PATH];    
        char                      szPort[NW_MAX_PATH];         
        char                      szFriendlyName[NW_MAX_PATH]; 
}DeviceDetail;

typedef enum 
{
    DEV_TYPE_PC_CARD            = 0, 
    DEV_TYPE_MINI_PCI           = 1,   
    DEV_TYPE_EXPRESS_CARD       = 2
    DEV_TYPE_SM_BUS_MINI_PCI    = 3,   
} DeviceFormFactorType;

typedef enum
{
    DEV_NONE        = 0,       
    DEV_EVDO        = 4,      
    DEV_UMTS        = 7,      
}DeviceTechType;




main.cpp
int main(int argc, char* argv[])
{
    SdkWrapper          sdk;
    NvtlEventCallback   cb;
    DeviceInfoStruct    device_info;
    NetworkInfoStruct   network_info;
    DeviceDetail        device_list[5];
    unsigned long       device_list_size = 5;


    memset(device_list, 0, device_list_size*sizeof(DeviceDetail));
    rval = sdk.GetAvailableDevices( device_list, &device_list_size)
    printf("Found %ld devices\n", device_list_size);
 }

This is what I have tried so far:

from ctypes import *

eformfactor = (DEV_TYPE_PC_CARD,
               DEV_TYPE_MINI_PCI,
               DEV_TYPE_EXPRESS_CARD,
               DEV_TYPE_SM_BUS_MINI_PCI,) = map(c_int, xrange(4))



edevicetechtype = (DEV_NONE,
                   DEV_EVDO,
                   DEV_UMTS) = map(c_int, xrange(3)) 


class devdetails(Structure):
    _fields_ = [("eformfactor" ,eformfactor),
                ("edevicetechtype", edevicetechtype),
                ("szDescription", c_char * 255),
                ("szFriendlyName", c_char * 255),
                ("szPort", c_char * 255)]


device_list_size = c_int * 5
#
dll = cdll.LoadLibrary("C:\Program Files\Sdk.dll")
session = dll.CreateSession()
dev_list = dll.NvtlCommon_GetAvailableDevices(session, pointer(devdetails), byref(device_list_size))


Thanks in advance for your help.

Regards

[dilbert_here00]

Any body who can help me with this?

Thanks & Regards