Jump to content

Cluster to Struct Conversion

Jolt

By Jolt,
in Calling External Code

Recommended Posts

Jolt Newbie

Jolt

Posted
Posted (edited)

I recently posted this example code to ni.com - https://decibel.ni.com/content/docs/DOC-40315

 

Motivation: sometimes we need to call a C function that takes mixed data types in the form of a C Structure. While it is fairly easy to replicate the C Stuct as a LV Cluster it can be pretty hard to pass this to the C DLL due to the way LV and C understand data formats and byte packing.

 

Essentially I tried to create a completely universal (or close thereto) Cluster to Struct and Back Again set of functions. These consider packing/padding, data alignment, endian-ness, etc. I included some examples that have arrays and strings in the cluster as well as data pointers.

 

I see this topic being fairly active here on LAVA and to a slightly lesser degree at NI.com

 

Anyway, I don't know if the code will help anyone but I would be helped by any feedback or suggestions if anyone does try it!

 

Cheers,

-Jolt

Edited by Jolt
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
Go to topic listing

  • Similar Content

    • Fred chen
      How to deal with clusters containing clusters?
      By Fred chen
      Hi
       
      When I call the DLL, there is a structure:
      struct Signal { uint32 nStartBit; uint32 nLen; double nFactor; double nOffset; double nMin; double nMax; double nValue; uint64 nRawValue; bool is_signed; char unit[11]; char strName[66]; char strComment[201]; };  
       
      There is another  Message structure to the above Signal:
       
      struct Message { uint32 nSignalCount; uint32 nID; uint8 nExtend; uint32 nSize; Signal vSignals[513]; char strName[66]; char strComment[201]; }  
        The point is  Signal vSignals[513];
       
      I've tried to solve it like this，but the program will crash.
       
      How to create struct Message ，any good suggestions?  Thanks a lot.
       

      message.vi
    • Taylorh140
      Variant Array to Cluster Xnode
      By Taylorh140
      After working on the set cluster element by name xnode, it made me realize i could use the same concept to convert a variant array to a cluster. The technique is actually pretty simple, the xnode generates a case structure for each element in a cluster in cluster order, wherein a bundle by name is used to set the value and an unbundle by name is used to get the type, a variant to data is used to convert the data. This has some benefits over some methods, you are not limited to 255 elements, although that is not usually the case some of us are paranoid that clusterosaurus giganticous will be larger than expected. It also has a draw back  that is that when converting from a variant array all the elements must have unique, non-blank names, and this is usually the case. 

      I think this technique (though very brute-force) might be useful for some other things let me know what you guys think.

      VariantArrayToCluster.zip
    • Taylorh140
      Set Cluster Element Xnode (experimental)
      By Taylorh140
      This Xnode allows setting a cluster element by label string without using references. I pulled a great deal of inspiration from Hooovahhs Variant Array to cluster xnode, which i suppose this could be used for, another benefit is its not limited to 255 elements. Its mostly experimental because I haven't used it much. 
       
      SetClusterElement.zip

      SetClusterElementLV2013.zip
    • Porter
      Auto-Wire Array to Cluster
      By Porter
      Is there any way to automatically wire an index array block to a bundle by name block?

      Auto-wire (pressing space) just adds one wire.
      Note that my cluster contains data of different types so converting the cluster to an array doesn't work.
      If there is a quick-drop shortcut for this I would be very impressed.
    • GregFreeman
      Write to Binary File Cluster Size [x-post to ni forums]
      By GregFreeman
      Edit: found this in context help: Arrays and strings in hierarchical data types such as clusters always include size information.
       
      http://forums.ni.com/t5/LabVIEW/Write-to-Binary-File-Cluster-Size/td-p/3199224
       
      I have a cluster of data I am writing to a file (all different types of numerics, and some U8 arrays). I write the cluster to the binary file with prepend array size set to false. It seems, however, that there is some additional data included (probably so LabVIEW can unflatten back to a cluster). I have proven this by unbundling every element and type casting each one, then getting string lengths for the individual elements and summing them all. The result is the correct number of bytes. But, if I flatten the cluster to string and get that length, it's 48 bytes larger and matches the file size. Am I correct in assuming that LabVIEW is adding some additional metadata for unflattening the binary file back to a cluster, and is there any way to get LabVIEW to not do this?
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.

  I accept