# New uORB message definition problem

**URL:** <https://discuss.px4.io/t/new-uorb-message-definition-problem/23465>\
**Category:** PX4 Autopilot\
**Created:** [July 26, 2021, 4:30pm UTC](https://discuss.px4.io/t/new-uorb-message-definition-problem/23465 "2021-07-26T16:30:09Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![Antefos](https://discuss.px4.io/user_avatar/discuss.px4.io/antefos/32/8426_2.png) [@Antefos](https://discuss.px4.io/u/Antefos)\
**Post date:** [July 26, 2021, 4:30pm UTC](https://discuss.px4.io/t/new-uorb-message-definition-problem/23465/1 "2021-07-26T16:30:09Z")

</div>

Hi everyone, I’m trying to add an HOSM control to PX4 architecture based on the linearization property of the system for a multicopter.  
In order to do to i need to add new topics but i have some errors.

I’ve created a .msg file than added its name to the CmakeList…  
The error i got is the following:

‘\_\_orb\_control\_feedback’ was not declared in this scope

 ![Screenshot from 2021-07-26 18-29-45](https://discuss.px4.io/uploads/default/original/2X/b/b4c6d1468c1fe7b9a8f4642271f63ad5af3b78d4.png)

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<div class="post-metadata">

**Author:** ![Danduril](https://discuss.px4.io/user_avatar/discuss.px4.io/danduril/32/10295_2.png) [@Danduril](https://discuss.px4.io/u/Danduril)\
**Post date:** [July 26, 2021, 5:45pm UTC](https://discuss.px4.io/t/new-uorb-message-definition-problem/23465/2 "2021-07-26T17:45:36Z")

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I tried some of my typical mistakes but could not reproduce that exact error. All my mistakes result in:

`: fatal error: use of undeclared identifier ' __orb_bus_foo'; did you mean '__ orb_bus_guid'`

What was your exact error message?

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<div class="post-metadata">

**Author:** ![Antefos](https://discuss.px4.io/user_avatar/discuss.px4.io/antefos/32/8426_2.png) [@Antefos](https://discuss.px4.io/u/Antefos)\
**Post date:** [July 27, 2021, 8:41am UTC](https://discuss.px4.io/t/new-uorb-message-definition-problem/23465/4 "2021-07-27T08:41:02Z")

</div>

![Screenshot from 2021-07-27 10-38-51](https://discuss.px4.io/uploads/default/original/2X/5/51b1b8d67226b515e38a7fbade839a5c36dc0b9e.png)

The error in the terminal is this one.

The strange thing is that i have another message defined that give no problem at all.

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<div class="post-metadata">

**Author:** ![Danduril](https://discuss.px4.io/user_avatar/discuss.px4.io/danduril/32/10295_2.png) [@Danduril](https://discuss.px4.io/u/Danduril)\
**Post date:** [July 27, 2021, 4:01pm UTC](https://discuss.px4.io/t/new-uorb-message-definition-problem/23465/5 "2021-07-27T16:01:48Z")

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I can repro like this (`msg/foo.msg`):

```auto
uint64 timestamp
float32 foo

# TOPICS custom_name

```

`build/px4_sitl/uORB/topics/foo.h`:

```auto
...
/* register this as object request broker structure */
ORB_DECLARE(custom_name);

```

I have learned that when I want to add topics using `# TOPICS` I have to explicitly list the default name, too.

```auto
uint64 timestamp
float32 foo

# TOPICS foo custom_name

```

Ofc, I don’t know if that’s what has happened in your case.

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<div class="post-metadata">

**Author:** ![Antefos](https://discuss.px4.io/user_avatar/discuss.px4.io/antefos/32/8426_2.png) [@Antefos](https://discuss.px4.io/u/Antefos)\
**Post date:** [July 27, 2021, 4:36pm UTC](https://discuss.px4.io/t/new-uorb-message-definition-problem/23465/6 "2021-07-27T16:36:26Z")

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Wow, that solved my problem.

Thanks a lot, it could have taken days to me to find out the problem.