launch.json and tasks.json file setting ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed

I am having an issue with compiling my Mystring (very simple and easy beginner C++ code) and can't resolve this error:

Error:"ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)"
Warning: "(base) Fans-MBP:Section14 fanyang$ cd "/Users/fanyang/Documents/Tests/Tests/FirstWorkspace/Section14/" && g++ main.cpp -o main && "/Users/fanyang/Documents/Tests/Tests/FirstWorkspace/Section14/"main
In file included from main.cpp:2:
./Mystring.h:30:23: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
    Mystring(Mystring &&source);
                      ^
./Mystring.h:34:34: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
    Mystring &operator=(Mystring &&rhs);
                                 ^
./Mystring.h:37:35: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
    Mystring &operator+=(Mystring &&rhs);"

I am using VSCode (was using Codelite and switched to VSCode just yesterday and the code that ran fine now doesn't run).

Here are my task and launch files:

tasks.json:

{
    // See https://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "2.0.0",
    "tasks": [
        {
            "type": "shell",
            "label": "clang++ build active file",
            "command": "/usr/bin/clang++",
            "args": [
                "-std=c++17",
                "-stdlib=libc++",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}"
            ],
            "options": {
                "cwd": "${workspaceFolder}"
            },
            "problemMatcher": ["$gcc"],
            "group": {
                "kind": "build",
                "isDefault": true
            }
        }
    ]
}

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": "clang++ - Build and debug active file",
            "type": "cppdbg",
            "request": "launch",
            "program": "${fileDirname}/${fileBasenameNoExtension}",
            "args": [],
            "stopAtEntry": true,
            "cwd": "${workspaceFolder}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "lldb",
            "preLaunchTask": "clang++ build active file"
        }
    ]
}