Debugging

In the following, we describe two different ways how we can debug our code directly in VS Code:

• Using the CodeLLDB extension together with the lldb debugger
• Using CMake Tools + Microsoft's C/C++ extension

The author suggests to use the latter because of its simplicity.

Compile with debug flags

Before using a debugger, it is probably a good idea to compile our code in debug mode. If you haven't done so,

• Run >CMake: Select a Variant and select Debug
• Run >Cmake: Build

This creates a (new) build directory (build.Clang-21.1.2-Debug in our case).

Set a breakpoint

We want to debug ./examples/ex2.cpp.

To set a breakpoint,

• Open the source file ./examples/ex2.cpp
• Click next to the line number 9

The red dot indicates that a breakpoint has been set on this specific line.

CodeLLDB

In contrast to Microsoft's C/C++ extension, clangd does not come with a debugging feature.

Here we show how to use the CodeLLDB extension together with the lldb debugger.

Install the extension

To install/enable the extension, follow the same steps as in the previous sections.

Create a template launch.json

To use the debugger in VS Code, we have to provide a launch.json file. Fortunately, CodeLLDB makes it fairly easy to generate a basic template:

• Click on Run and Debug in the activity bar (triangle with the bug)
• Choose create a launch.json file
• Select CodeLLDB

This creates a launch.json in our project settings folder .vscode:

Apply the following changes:

Run the debugger

• Click on Run and Debug in the activity bar
• Click the green play icon next to Debug ex2
• Start debugging

We can now examine variables, step into functions, etc.

It is also possible to use the usual commands in the Debug Console:

Add another configuration

If we want to debug a different executable or run the same executable with different input arguments, we can simply add a new configuration to the launch.json file:

Then we select the appropriate configuration from the drop down menu next to the green play icon in the Run and Debug window:

CMake Tools + Microsoft's C/C++ extension

Combining CMake Tools with the debugging features from Microsoft's C/C++ extension makes it super easy to start a debugging session.

However, we want to note that other approaches, e.g. using a launch.json file, can be more flexible and powerful.

Install the extension

To install/enable the extension, follow the same steps as in the previous sections.

Settings

In the bottom right corner in the screenshot above, VS Code already warns us that we have both clangd and Microsoft's C/C++ extension installed. Their language server features don't work well together.

Since we only want the debugging features from the Microsoft's C/C++ extension, we will disable its Intellisense as suggested by VS Code.

We can do this by either clicking Disable Intellisense in the pop-up window or by updating the user settings JSON file:

Run the debugger

• Run >CMake: Select Launch/Debug Target
• Select ex2
• Run >CMake: Debug
• Start debugging

We can now examine variables, step into functions, etc.

It is also possible to use the usual commands in the Debug Console:

To change executable, we simply run >CMake: Select Launch/Debug Target again and select a different target.