# Tips for debugging SMTK
**URL:** https://discourse.kitware.com/t/tips-for-debugging-smtk/304
**Category:** Tips and Tricks
**Created:** [August 29, 2019, 3:34pm UTC](https://discourse.kitware.com/t/tips-for-debugging-smtk/304 "2019-08-29T15:34:33Z")
**Posts on this page:** 1
**Page:** 1
### Author:  [@dcthomp](https://discourse.kitware.com/u/dcthomp)
#### Post date: [August 29, 2019, 3:34pm UTC](https://discourse.kitware.com/t/tips-for-debugging-smtk/304/1 "2019-08-29T15:34:33Z")
NB: This topic is a “wiki page,” which means anyone (not just the author) can edit it. Please add your own tips below.
# LLDB
Below are some niceties for using lldb with SMTK. There may be equivalents for gdb; if so, please add them to a new top-level section below this one.
## Model entity type bits
If you deal with `smtk::model::Entity` objects a lot, you’ll notice that the `m_entityFlags` member is always a combination of values from [`smtk/model/EntityTypeBits.h`](https://gitlab.kitware.com/cmb/smtk/tree/master/smtk/model/EntityTypeBits.h#L101) . The enum values in the header file are hexadecimal and easier to read in a base that is some power of 2. You can have lldb print them in hexadecimal like so:
```auto
ty fo add --format hex smtk::model::BitFlags
```
Adding the line above to your `~/.lldbinit` file will make it the default behavior.
## Inspecting UUIDs
If you use lldb, you can have it print UUIDs out compactly instead of the verbose and unhelpful unsigned char array. To do so,
1. Create an `.lldb` directory in your home directory
```auto
mkdir ~/.lldb
```
1. Create a text file in `~/.lldb` named `uuid.py` with the following contents:
```python
import lldb
def uuid_summary(value, *rest):
"""valobj: an SBValue which you want to provide a summary for
internal_dict: an LLDB support object not to be used"""
rawd = value.GetChildMemberWithName('data')
s = ''.join('%02x'%i for i in rawd.data.uint8)
return 'UUID(' + s[0:8] +'-' + s[8:12] + '-' + s[12:16] + '-' + s[16:20] + '-' + s[20:32] + ')'
def __lldb_init_module(debugger, *rest):
summary = lldb.SBTypeSummary.CreateWithFunctionName('uuid.uuid_summary')
summary.SetOptions(lldb.eTypeOptionHideChildren)
debugger.GetDefaultCategory().AddTypeSummary(lldb.SBTypeNameSpecifier('boost::uuids::uuid', False), summary)
```
1. Either add the line below to your `~/.lldbinit` file or create a new file named `~/.lldbinit` with the line below
```auto
command script import ~/.lldb/uuid.py
```
## Qt
If you are working with SMTK’s Qt extensions, you may be interested in [these Qt5 formatters](https://github.com/sdonegan/Qt5DataFormatters) that let you inspect QString and some of Qt’s container classes.
## Shared Pointers
SMTK provides some lldb python functions in `utilities/lldb/shared_ptr.py` that allow you to stop execution when a particular object’s shared-pointer use-count changes. You can import these functions into your lldb function by running
```auto
command script import /path/to/smtk/utilities/lldb/shared_ptr.py
```
Then, at a point where you have a pointer to some class that inherits `enable_shared_from_this` (like all smtk::resource::PersistentObject and smtk::operation::Operation classes), you can run the following
```auto
useCountWatch
# e.g.,
# useCountWatch smtk::resource::Resource 0x142f240f0
```
to break when that object’s use count changes. Once you have a watchpoint on the use-count, there’s also a function to dump a stack trace to a file whenever the use count changes:
```auto
useCountTrace []
# e.g.,
# useCountTrace 0x142f240f0 /tmp/trace.txt 4
```
If calling the `useCountWatch` example above created watchpoint 1, then the following will add a script to the watchpoint to dump a stack trace and continue:
```auto
wa co add 1
> useCountTrace 0x142f240f0 /tmp/trace.txt
> c
> DONE
```