What is the difference between the use of g++ and gcc command line?

I am learning to use threading so I am trying to run code utilizing the thread class so that I can run functions concurrently. However, trying to compile it in the terminals terminal, it says that thread and its object t1 is not declared.

image of the error

I thought g++ doesn't support it but I also include in its argument to support c++11

image of the compiling command line

Any idea what I should I do about this error?

Code is provided below(an example from a website):

#include <string>
#include <iostream>
#include <thread>

using namespace std;

// The function we want to execute on the new thread.
void task1(string msg)
{
    cout << "task1 says: " << msg;
}

int main()
{
    // Constructs the new thread and runs it. Does not block execution.
    thread t1(task1, "Hello");

    // Do other things...

    // Makes the main thread wait for the new thread to finish execution, therefore blocks its own execution.
    t1.join();
}