correct form of struct for strings (or byte array) when importing Labview DLL into python (using ctypes) -


i'm trying import dll (created in labview) python. i've reduced simple labview vi, string goes cluster, cluster function in dll i.e. function is: void testcluster(cluster *outputcluster) can strings , arrays read in cluster. think don't have correct struct (?).

has done this? there's partial guide: http://www.ni.com/white-paper/8911/en/

it might due little knowledge of ctypes in python too.

sample python code import:

#!/usr/bin/env python import sys, os, string ctypes import *  class bytearraystructure(structure):     _fields_ = [("dimsize", c_int),("bytes", c_uint8 )]  class clusterstructure(structure):     _fields_ = [("stringfield", c_char*4 ),                 ("bytearray", bytearraystructure )]  dll = cdll.loadlibrary("test.dll") libc = cdll.msvcrt  def testmain():     retvalue = 0     try:         clusterin = clusterstructure()         dll.testcluster( byref(clusterin) )          print clusterin.bytearray.bytes          print cast(clusterin.bytearray.bytes,c_char_p)      except valueerror, argument:         retvalue = "error: " + str(valueerror) + "  " + str(argument)     return retvalue  testmain()

edit:

structs test.h,

typedef struct {     int32_t dimsize;     uint8_t elt[1]; } uint8arraybase; typedef uint8arraybase **uint8array; typedef struct {     lstrhandle elt1;     uint8array unsignedbytearray; } cluster;  void __cdecl testcluster(cluster *outputcluster);  mgerr __cdecl lvdllstatus(char *errstr, int errstrlen, void *module);  /* * memory allocation/resize/deallocation apis type 'uint8array' */ uint8array __cdecl allocateuint8array (int32 elmtcount); mgerr __cdecl resizeuint8array (uint8array *hdlptr, int32 elmtcount); mgerr __cdecl deallocateuint8array (uint8array *hdlptr);

thanks :)

you need allocate , deallocate strings, arrays, , clusters because labview expects full , complete object owned its memory manager instead of python's in case needs modify them (add/remove array elements or string characters). example, vikit has labview-built library uses strings , clusters in entry points.

for more information, while link reverse (a c dll called labview), examples here include clusters, strings, , arrays: calling c/c++ dlls containing simple , complex datatypes labview.


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