Use gdb in vscode with -lm flag

As of https://code.visualstudio.com/docs/cpp/launch-json-reference, I can only attach to an already existing binary with vscode (in the example being a.out), but I would like to have it in a way so that I can debug without having to compile manually first (with the -lm flag). How would I go about that?

Solution

Figured it out. Instead of only using a launch.json, I also used a task.json as follows in order to build the c file first:

{
    "version": "2.0.0",
    "tasks": [
        {
          "label": "build C file",
          "type": "shell",
          "command": "gcc -g -o ${workspaceFolder}/sum/main ${file} -lm",
          "problemMatcher": [],
          "group": {
            "kind": "build",
            "isDefault": true
          }
        }
      ]
}

In the launch.json, I use the task as a preLaunchTask:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "C Debug",
      "type": "cppdbg",
      "request": "launch",
      "program": "${workspaceFolder}/sum/main", // Dummy value
      "args": [],
      "stopAtEntry": true,
      "cwd": "${workspaceFolder}",
      "environment": [],
      "externalConsole": true,
      "MIMode": "gdb",
      "miDebuggerPath": "/usr/bin/gdb",
      "preLaunchTask": "build C file",
    }
  ],
}

More info on tasks here: https://code.visualstudio.com/docs/editor/tasks