# How to utilise Cvb.Error.CVC\_ERROR\_CODES with C#

**URL:** <https://forum.commonvisionblox.com/t/how-to-utilise-cvb-error-cvc-error-codes-with-c/474>\
**Category:** C-style API\
**Tags:** csharp\
**Created:** [June 19, 2018, 2:04pm UTC](https://forum.commonvisionblox.com/t/how-to-utilise-cvb-error-cvc-error-codes-with-c/474 "2018-06-19T14:04:41Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![Amicelli](https://avatars.discourse-cdn.com/v4/letter/a/a698b9/32.png) [@Amicelli](https://forum.commonvisionblox.com/u/Amicelli)\
**Post date:** [June 19, 2018, 2:04pm UTC](https://forum.commonvisionblox.com/t/how-to-utilise-cvb-error-cvc-error-codes-with-c/474/1 "2018-06-19T14:04:41Z")

</div>

Hello,

as my brain is malfunctioning today, maybe you can shed some light. I want to display a readable text of the error code on my GUI. Therefore, I cast it first. This seems to be fine, if it returns CVC\_E\_OK but as soon as the number is negative, it does not cast it to an enum and displays me the timeout as -474837744 (or something similiar :)).

Can you shed some light please how I can improve my function?

```
  Cvb.Error.CVC_ERROR_CODES errorCode = (Cvb.Error.CVC_ERROR_CODES)Cvb.Driver.IGrabber.Snap(_hImg);
  if (Cvb.Error.CVC_ERROR_CODES.CVC_E_OK == errorCode) 
  {
    Image = _hImg;
    // Save Images
    string imageName = Settings.FilePath + Settings.FileName + "_Camera" + _cameraPort + "_" + fileNamePostfix + ".bmp";

    if (!Cvb.Image.WriteImageFile(_hImg, imageName))
    {
      TestText = "Failed to save image: " + imageName;
    }
    TestText = "Done";
  }
  else
  {
    TestText = "Error snapping image: " + errorCode.ToString("g"); 
  }

```

![image](https://canada1.discourse-cdn.com/flex027/uploads/commonvisionblox/original/1X/adefe4aaaff99ba72985370c61fdd970b66f61eb.jpg)

Do you have a code-snippet showing the optimal solution for it (thus it says “timeout”).

Thanks in advance.

---

<div class="post-metadata">

**Author:** ![Frank](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/frank/32/42_2.png) [@Frank](https://forum.commonvisionblox.com/u/Frank)\
**Post date:** [June 20, 2018, 5:53am UTC](https://forum.commonvisionblox.com/t/how-to-utilise-cvb-error-cvc-error-codes-with-c/474/2 "2018-06-20T05:53:59Z")

</div>

I’m also interested in a nice solution for this. It would have to be something similar to what is available in the C++ API with CVC\_ERROR\_FROM\_HRES.

---

<div class="post-metadata">

**Author:** ![illusive](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/illusive/32/61_2.png) [@illusive](https://forum.commonvisionblox.com/u/illusive)\
**Post date:** [June 20, 2018, 7:40am UTC](https://forum.commonvisionblox.com/t/how-to-utilise-cvb-error-cvc-error-codes-with-c/474/3 "2018-06-20T07:40:07Z")

</div>

You tried to simply cast the value returned by `Snap()` into a `Cvb.Error.CVC_ERROR_CODES` enum. That won’t work. Well, technically speaking it works, but it doesn’t yield anything useful. Functions in the C-API of :cvb: return either a `bool` value or a `HRESULT`-like value (there are very few - and unfortunate - exceptions to that rule). The `HRESULT` convention dictates that the uppermost bit of the return value is to be set if an error occurred (making the error check fairly easy: Anything less than zero is an error, zero or positive values aren’t). Values like -2147483644 (= 0x8000 0004) are, however, quite the piece of work to write into an enumeration. Add to that the fact that e.g. the old Borland C++ compilers did by default treat enums are 8-bit variables and you have the mess that prompted the pattern that is being used: Any function returning an error will internally always use the `CVC_ERROR` macro from _CVCError.h_ to generate its return values…

… and anyone wanting to evaluate the return value in terms of the `CVC_ERROR_CODES` will need to apply the inverse operation `CVC_ERROR_FROM_HRES` (all these two macros ever really do is set and unset the uppermost bit in the integer). When the original C# wrappers were written this pattern was simply transcribed to C#. C# has the added benefit of being able to directly convert the enum values to strings (you got that part right, however your integer value could not by mapped to one of the enum values and was therefore just output as a number), so in order to improve the output I’d recommend something like this:

```auto
Cvb.Error.CVC_ERROR_CODES errorCode = (Cvb.Error.CVC_ERROR_CODES)Cvb.Error.CVC_ERROR_FROM_HRES(Cvb.Driver.IGrabber.Snap(_hImg));

```

… and as you asked for suggestions to improve the code:

- use `var` where possible - especially if the name of the type involved is poorly readable
- I’m not a fan of Yoda conditions ([https://blog.codinghorror.com/new-programming-jargon/](https://blog.codinghorror.com/new-programming-jargon/), [https://en.wikipedia.org/wiki/Yoda\_conditions](https://en.wikipedia.org/wiki/Yoda_conditions)) as they are counter-intuitive when read (and readability greatly contributes to maintainability), but that is probably just a matter of preference
- in line 12 you overwrite the text you did potentially just set - probably not intended that way
- I’d recommend to stick with one naming convention for variable names; you used lower camel case for most of them, but camel case for `TestText`

```cs
  using Cvb;

  ...

  var errorCode = (Cvb.Error.CVC_ERROR_CODES)Error.CVC_ERROR_FROM_HRES(Driver.IGrabber.Snap(_hImg));
  if (errorCode == Error.CVC_ERROR_CODES.CVC_E_OK) 
  {
    Image = _hImg;
    // Save Images
    var imageName = string.Format("{0}{1}_Camera{2}_{3}.bmp", Settings.FilePath, Settings.FileName, _cameraPort, fileNamePostfix);
    if (!Cvb.Image.WriteImageFile(_hImg, imageName))
      testText = "Failed to save image: " + imageName;
    else
      testText = "Done";
  }
  else
  {
    testText = "Error snapping image: " + errorCode.ToString(); 
  }

```

That is about as readable as it gets with the C API. With [Cvb.Net](http://Cvb.Net) your code would roughly look like this:

```csharp
  var status = WaitStatus.Ok;
  var snappedImage = myDriver.GetSnapshot(myTimeout, out status);
  if (snappedImage != null)
  {
    var imageName = string.Format("{0}{1}_Camera{2}_{3}.bmp", Settings.FilePath, Settings.FileName, _cameraPort, fileNamePostfix);
    try
    {
      snappedImage.Save(imageName);
      testText = "Done";
    }
    catch(Exception ex)
    {
      testText = string.Format("Failed to save image {0}: {1}", imageName, ex.Message);
    }
  }
  else
    testText = status.ToString();

```

Fairly similar. Slightly more pleasant to read, mostly due to the lack of all-caps names 🙂

---

<div class="post-metadata">

**Author:** ![Amicelli](https://avatars.discourse-cdn.com/v4/letter/a/a698b9/32.png) [@Amicelli](https://forum.commonvisionblox.com/u/Amicelli)\
**Post date:** [June 27, 2018, 10:49am UTC](https://forum.commonvisionblox.com/t/how-to-utilise-cvb-error-cvc-error-codes-with-c/474/4 "2018-06-27T10:49:28Z")

</div>

Thank you illusive. This solved my issue. 😀

---

<div class="post-metadata">

**Author:** ![illusive](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/illusive/32/61_2.png) [@illusive](https://forum.commonvisionblox.com/u/illusive)\
**Post date:** [June 27, 2018, 12:46pm UTC](https://forum.commonvisionblox.com/t/how-to-utilise-cvb-error-cvc-error-codes-with-c/474/5 "2018-06-27T12:46:00Z")

</div>

Well, in that case I take the liberty of marking my own reply as “the solution” 😄