Problems with using nullptr in g++

[AlanG]

How do I check which C++ version my copy of g++ supports?

$ g++ --version
g++ (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
Copyright (C) 2013 Free Software Foundation, Inc.

My reason for asking is that it barfs on the
nullptr line below

using namespace std;
...
int main(){
int* pn = nullptr;
...
}

saying nullptr is not declared in this scope.
But I thought nullptr was one of the new keywords?
So I'm assuming g++ is working to an older version
of C++. Or have I misunderstood something about nullptr?
Is it in a different namespace?

[Peter87]

nullptr was added in C++11. To enable C++11 features you need to pass the compiler flag -std=c++11.

[JLBorges]

To compile the code as C++11, compile with the options -std=c++11 -pedantic-errors (both are required)
You may also want to use these additional options: -Wall -Wextra

Ideally, shun versions of the GNU implementation older than version 5.1.

[AlanG]

Thanks folks, that works.