Resizeing an array of LStrHandles within Call Library Functio Node crashes SubVI.

[kremp@fti-en.com]

Hello,

I try to resize an array of LStrHandles within a shared library. Here the C-code - attached a picture of the calling SubVI:

/* Call Library source file */

#include <stdio.h>
#include "extcode.h"

/* Typedefs */

typedef struct {
        long dimSize;
        LStrHandle elt[1];
        } TD1;
typedef TD1 **TD1Hdl;

long strArray(TD1Hdl arg1);
long strArray(TD1Hdl arg1)
{
        long err=0, count=2;

        err = DSSetHandleSize((UHandle)arg1, sizeof(long) + count*sizeof(LStrHandle));
        if(err) {
                printf("ERROR: 'DSSetHandleSize()': %ld\n", err);
                return err;
        };

        (*arg1)->dimSize = (*arg1)->dimSize;

        return noErr;

}

I know there are a lot of threads, I read some and also tried the provided source code but somehow LabVIEW crashes. I don't know if it is valueable but when I change the following line it does not crash:

(*arg1)->dimSize = (*arg1)->dimSize;

Thanks for any help,

Johannes

OS: RedHat

LV: 8.2 Prof

Message Edited by kremp@fti-en.com on 03-11-2009 12:26 PM

[rolfk · Accepted solution]

To be honest I'm not fully sure why that would crash but proper dealing is a lot more complicated than what you have done. The crash probably happens not in the C fucntion but on return of the function as LabVIEW tries to display the data. DSSetHandleSize() does not initialize the area it allocates additionally so there is likely garbage which LabVIEW then tries to interpret as string handles and consequently crashes.

You should also use NumericArrayResize() whenever possible as it takes care of various complications that can be hard to deal with on multi platform programs. NumericArrayResize() does use internally DSSetHSzClr() which initializes additional memory to 0. That would avoid the crash since LabVIEW does interpret NULL handles as the default for the according datatype, which would be here an empty string.

#include "extcode.h"

#if  IsOpSystem64Bit

#define uPtr uQ

#else

#define uPtr uL

#endif

typedef struct {

    int32 dimSize;

    LStrHandle elm[1];

} TDStrArr, **TDStrArrHdl;

MgErr MyArrayFunc(TDStrArrHdl arr)

{

    int32 count = 4;

    LStrHandle p;

    MgErr err = noErr;

    /* The array could be non empty so dispose of any elements in it that are bigger than what we need */

    for (i = (*arr)->dimSize - 1; i >= count; i--)

    {

      p = (*arr)->elm[i];

      if (p)

        DSDisposeHandle(p)

    }

    (*arr)->dimSize = i + 1;

    /* resize the array handle to get enough space */

    err = NumericArrayResize(uPtr, 1, (UHandle*)&arr, count);

    if (err)

      return err;

    /* Fill in the data as desired */

    for (i = 0; !err && i < count; i++)

    {

      p = (*arr)->elm[i];

#if !complicated

      err = NumericArrayResize(uB, 1, (UHandle*)&p, 1);

#else

      if (p)

      {

        err = DSSetHSzClr(p, sizeof(int32));

      }

      else

      {

        p = DSNewHClr(sizeof(int32));

        if (p)

          (*arr)->elm[i] = p;

        else

          err = mFullErr;

      }    

#endif

      if (!err)

        err = LStrPrintf(p, "%ld", i);

    }

    (*arr)->dimSize = i;

    return err;

}

Rolf Kalbermatter

Message Edited by rolfk on 03-11-2009 08:40 PM

[kremp@fti-en.com]

You were right - not the C-function crashed but LabVIEW when the C-function returned. 'NumericArrayResize' was the answer. I tried 'SetCINArraySize' before but this caused a crash in the C-function immediately. I used the same C-code in a Code Interface Node and there 'SetCINArraySize' worked very well.

I thought 'NumericArrayResize' should only be used to resize "numeric" arrays but I assume as a string array is also based on a numeric array 'NumericArrayResize' is working for string arrays as well.

Thank you very much.

Johannes

[winkler]

You made my day! Thanks a lot!!!