stoi was not declared in this scope, despite using C++11

I am using c++11 with MinGW compiler on code::blocks. When I type:

int x = stoi("4");

I get the error: 'stoi' was not declared in this scope, however it should be, and I can't figure out why it isn't.

This has been driving me up the wall, and I would love it if someone could help. Thanks a bunch :)