Debugging

Test First
Before you go through the pain of debugging use the Test framework to check if the standard tests work properly. If they do not run complete there is possibly a broken installation.

Command Line
The debugging of FreeCAD is supported by a few internal mechanisms. The command line version of FreeCAD provides some options for debugging support.

These are the currently recognized options in FreeCAD 0.19:

Generic options: -v [ --version ]         Prints version string -h [ --help ]            Prints help message -c [ --console ]         Starts in console mode --response-file arg      Can be specified with '@name', too --dump-config            Dumps configuration --get-config arg         Prints the value of the requested configuration key

Configuration: -l [ --write-log ]       Writes a log file to: $HOME/.FreeCAD/FreeCAD.log (Linux) $HOME/Library/Preferences/FreeCAD/FreeCAD.log (macOS) %APPDATA%\FreeCAD\FreeCAD.log (Windows) --log-file arg           Unlike to --write-log this allows to log to an                             arbitrary file -u [ --user-cfg ] arg    User config file to load/save user settings -s [ --system-cfg ] arg  System config file to load/save system settings -t [ --run-test ] arg    Test case - or 0 for all -M [ --module-path ] arg Additional module paths -P [ --python-path ] arg Additional Python paths --single-instance        Allow to run a single instance of the application

Generating a Backtrace
If you are running a version of FreeCAD from the bleeding edge of the development curve, it may "crash". You can help solve such problems by providing the developers with a "backtrace". To do this, you need to be running a "debug build" of the software. "Debug build" is a parameter that is set at compile time, so you'll either need to compile FreeCAD yourself, or obtain a pre-compiled "debug" version.

For Linux
Linux Debugging →

Prerequisites:


 * software package gdb installed
 * a debug build of FreeCAD (at this time only available by building from source)
 * a FreeCAD model that causes a crash

Steps: Enter the following in your terminal window:

Find FreeCAD binary on your system:

GNUdebugger will output some initializing information. The (gdb) shows GNUDebugger is running in the terminal, now input:

FreeCAD will now start up. Perform the steps that cause FreeCAD to crash or freeze, then enter in the terminal window:

This will generate a lengthy listing of exactly what the program was doing when it crashed or froze. Include this with your problem report.

Print the values of the local variables also. This can be combined with a number to limit the number of frames shown.

For macOS
macOS Debugging →

Prerequisites:


 * software package lldb installed
 * a debug build of FreeCAD
 * a FreeCAD model that causes a crash

Steps: Enter the following in your terminal window:

LLDB will output some initializing information. The (lldb) shows the debugger is running in the terminal, now input:

FreeCAD will now start up. Perform the steps that cause FreeCAD to crash or freeze, then enter in the terminal window:

This will generate a lengthy listing of exactly what the program was doing when it crashed or froze. Include this with your problem report.

List Libraries Loaded by FreeCAD
(Applicable to Linux and macOS)

Sometimes it's helpful to understand what libraries FreeCAD is loading, specifically if there are multiple libraries being loaded of the same name but different versions (version collision). In order to see which libraries are loaded by FreeCAD when it crashes you should open a terminal and run it in the debugger. In a second terminal window, find out the process id of FreeCAD:

Use the returned id and pass it to :

This prints a long list of loaded resources. So for example, if trying to ascertain if more than one Coin3d library versions is loaded, scroll through the list or search directly for Coin in the output:

Python Debugging
For a more modern approach to debugging Python, see these posts:
 * Debugging macros with VS 2017
 * Python workbenches debugging
 * python3.dll, Qt5Windgets.dll, Qt5Gui.dll and Qt5Core.dll not found

winpdb
winpdb Debugging →

Here is an example of using Winpdb inside FreeCAD:

We need the Python debugger: Winpdb. If you do not have it installed, on Ubuntu/Debian install it with:

Now lets setup the debugger.


 * 1) Start Winpdb.
 * 2) Set the debugger password to "test": Go to menu File → ''Password" and set the password.

Now we will run a test Python script in FreeCAD step by step.


 * 1) Run winpdb and set the password (e.g. test)
 * 2) Create a Python file with this content


 * 1) Start FreeCAD and load the above file into FreeCAD
 * 2) Press F6 to execute it
 * 3) Now FreeCAD will become unresponsive because the Python debugger is waiting
 * 4) Switch to the Windpdb GUI and click on "Attach". After a few seconds an item "" appears where you have to double-click
 * 5) Now the currently executed script appears in Winpdb.
 * 6) Set a break at the last line and press F5
 * 7) Now press F7 to step into the Python code of Draft.makeWire

Visual Studio Code (VS Code)
VS Code Debugging →

Prerequisites:


 * ptvsd package needs to be installed in a python 3 outside of FreeCAD, then copy the module to FreeCAD's python library folder.

pypi page

Visual Studio Code documentation for remote debugging

Steps:
 * Add following code at the beginning of your script


 * Add a debug configuration in Visual Studio Code.
 * The config should look like this :

"configurations": [ {           "name": "Python: Attacher", "type": "python", "request": "attach", "port": 5678, "host": "localhost", "pathMappings": [ {                   "localRoot": "${workspaceFolder}", "remoteRoot": "." }           ]        },


 * In VS Code add a breakpoint anywhere you want.
 * Launch the script in FreeCAD. FreeCAD freeze waiting for attachment.
 * In VS Code start debugging using created configuration. You should see variables in debugger area.
 * When setting breakpoints, VS Code will complain about not finding the .py file opened in the VS Code editor.
 * Change "remoteRoot": "." to "remoteRoot": " "
 * For example, if the Python file resides in /home/FC_myscripts/myscript.py
 * Change to: "remoteRoot": "/home/FC_myscripts"
 * If you're just debugging FreeCAD macros from the FreeCAD macro folder, and that folder is "C:/Users/ /AppData/Roaming/FreeCAD/Macro", then use:
 * "localRoot": "C:/Users/ /AppData/Roaming/FreeCAD/Macro",
 * "remoteRoot": "C:/Users/ /AppData/Roaming/FreeCAD/Macro"
 * If your macro can't find ptvsd despite having installed it somewhere precede 'import ptvsd' with

where the path is to the directory where ptvsd got installed In the Mac package it is /Applications/FreeCAD.App/Contents/Resources/bin/python
 * On the left bottom edge of VSCode you can choose the Python executable - it's best to make this the version packaged with FreeCAD.

You can locate it on your system by typing

into FreeCAD's Python console.

Debugging OpenCasCade
For developers needing to dig deeper in to the OpenCasCade kernel, user @abdullah has created a thread orientation discussing how to do so.