Can I import a cluster with strings (or a byte array) from a Labview DLL into python (using ctypes)

[Jeff_Tech]

I've saved a DLL (created in Labview) and i'm trying to import it into python, as per the guide, http://www.ni.com/white-paper/8911/en/

I can get other types except strings and arrays to read in from a cluster. I've reduced it to a very simple vi: a string goes into a cluster, the cluster is a function in the DLL i.e. the function is:

void TestCluster(Cluster *outputCluster)

I think I just don't have the correct Struct (?).

Has anyone done this? It might also be due to my little knowledge of ctypes in Python too.

Theres a similar item: http://forums.ni.com/t5/LabVIEW/Loading-Labview-DLL-from-Python-Hits-Error/m-p/2756534/highlight/tru...

Do I have to use the CLN? (I tried but couldn't work it out)

Sample Python code for the import:

#!/usr/bin/env python
import sys, os, string
from 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()

[Jeff_Tech]

Is it possible to match up with the structs from the test.h file or am I missing something? (Does Labview allow this? or is the memory not accessible? or does the CLN have to be used?)

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 for type 'Uint8Array'
*/
Uint8Array __cdecl AllocateUint8Array (int32 elmtCount);
MgErr __cdecl ResizeUint8Array (Uint8Array *hdlPtr, int32 elmtCount);
MgErr __cdecl DeAllocateUint8Array (Uint8Array *hdlPtr);

[rolfk]

You overlooked the definition of

**Uint8Array

You see the double * in front?

That means it is a pointer to a pointer not just a pointer nor the entire structure entirely embedded in the cluster!

Same for the LStrHandle element in the cluster, that is also a pointer to a pointer to a similar structure.