将Labview DLL导入python（使用ctypes）时，字符串（或字节数组）的结构形式正确

Question

I'm trying to import a DLL (created in Labview) into python. I've reduced it to a very simple Labview VI, a string goes into a cluster, the cluster is a function in the DLL ie the function is: void TestCluster(Cluster *outputCluster) I can get everything but strings and arrays to read in from a cluster. I think I just don't have the correct Struct (?).

Has anyone done this? There's a partial guide: http://www.ni.com/white-paper/8911/en/

It might also be due to my little knowledge of ctypes in Python too.

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()

edit:

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

Thanks :)

Answer 1

You need to allocate and deallocate strings, arrays, and clusters because LabVIEW expects a full and complete object owned by its memory manager instead of Python's in case it needs to modify them (add/remove array elements or string characters). For example, VIKit has a LabVIEW-built library that uses strings and clusters in its entry points.

• Allocating a string in C
• Allocating an array of clusters

For more information, while this link is the reverse (a C DLL called from LabVIEW), the examples here include clusters, strings, and arrays: Calling C/C++ DLLs Containing Simple and Complex Datatypes from LabVIEW .