Sunday, 2 February 2020

Debugging C++ program in VSCode on Linux

Let's assume we have VSCode running in Ubuntu 18.04 and the following project structure:

cpp-demo/
cpp-demo/main.cpp
cpp-demo/src/foo.cpp
cpp-demo/include/foo.hpp


Let's assume we want to name the build output cpp-demo and place it at project's root directory:

cpp-demo/cpp-demo


To build and debug it we need to have

cpp-demo/.vscode/tasks.json
cpp-demo/.vscode/launch.json


Building


tasks.json contains build instructions. From the main menu (CTRL+SHIFT+P), choose Tasks: Configure Default Build Task and then g++ build active file. This will create a /.vscode/tasks.json file and open it in the editor. A task will be created there and we need to edit it like this:


cpp-demo/.vscode/tasks.json:


{
    "tasks": [
        {
            "type": "shell",
            "label": "g++ build active file",
            "command": "/usr/bin/g++",
            "args": [
                "-g",
                "${workspaceFolder}/main.cpp",
                "${workspaceFolder}/src/*.cpp",
                "-I",
                "${workspaceFolder}/include",
                "-o",
                "${workspaceFolder}/cpp-demo"
            ],
            "options": {
                "cwd": "/usr/bin"
            },
            "group": {
                "kind": "build",
                "isDefault": true
            }
        }
    ],
    "version": "2.0.0"
}

To run the build task defined in tasks.json, press Ctrl+Shift+B or from the main menu choose Tasks: Run Build Task. This will run g++ compiler and create the output binary. To run it, open a new terminal (in VSCode) and run:

./cpp-demo

For the full list of variables used in VSCode configuration files see Visual Studio Code Variables Reference and visual studio code - VSCode environment variables besides ${workspaceRoot} - Stack Overflow.


If we want g++ to have verbose output we can add to list of arguments:

"-v"

If we want linker to create map files (where we can see all mangled names of functions):

"-Xlinker",
"-Map=${workspaceFolder}/output.map",

Debugging


launch.json contains debugger settings.  From the main menu, choose Debug: Add Configuration... and then choose C++ (GDB/LLDB). You'll then see a dropdown for various predefined debugging configurations. Choose g++ build and debug active file. This creates a launch.json file and opens it in the editor. We need to edit it a bit e.g. to set correct name of the binary in program:

cpp-demo/.vscode/launch.json:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "g++ build and debug active file",
            "type": "cppdbg",
            "request": "launch",
            "program": "${workspaceFolder}/cpp-demo",
            "args": [],
            "stopAtEntry": true,
            "cwd": "${workspaceFolder}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "gdb",
            "setupCommands": [
                {
                    "description": "Enable pretty-printing for gdb",
                    "text": "-enable-pretty-printing",
                    "ignoreFailures": true
                }
            ],
            "preLaunchTask": "g++ build active file",
            "miDebuggerPath": "/usr/bin/gdb"
        }
    ]
}

Current working folder (the one opened in VSCode, cpp-demo in our case) is workspace so ${workspaceFolder} contains path to it.

To start debugging, place some breakpoints in source code, press F5 or from the main menu choose Debug: Start Debugging


References:


Get Started with C++ and Mingw-w64 in Visual Studio Code
Get Started with C++ and Windows Subsystem for Linux in Visual Studio Code
Configure launch.json for C/C++ debugging in Visual Studio Code
"g++" and "c++" compiler - Stack Overflow
c++ - What is the difference between g++ and gcc? - Stack Overflow
Compiling with g++

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