Compilation error with struct/class defined in a function - c++

Question

What is the problem with the following code. Because if I define the class inside the main function, the compilation fails and I don't understand the compiler error.
Test the code from here
Comment the 1st definition of drift_f (outside of main()) and uncomment the inner definition of drif_t (inside the main() function) and the compiler will get the following error message:
prog.cpp: In function ‘int main()’:
prog.cpp:27:24: error: template argument for ‘template<class> class std::allocator’ uses local type ‘main()::drift_t’
std::deque<drift_t> drift; drift.push_back(drift_t(0,0));drift.push_back(drift_t(-50,-50));
^
prog.cpp:27:24: error: trying to instantiate ‘template<class> class std::allocator’
prog.cpp:27:24: error: template argument 2 is invalid
prog.cpp:27:31: error: invalid type in declaration before ‘;’ token
std::deque<drift_t> drift; drift.push_back(drift_t(0,0));drift.push_back(drift_t(-50,-50));
^
prog.cpp:27:39: error: request for member ‘push_back’ in ‘drift’, which is of non-class type ‘int’
std::deque<drift_t> drift; drift.push_back(drift_t(0,0));drift.push_back(drift_t(-50,-50));
^
prog.cpp:27:69: error: request for member ‘push_back’ in ‘drift’, which is of non-class type ‘int’
std::deque<drift_t> drift; drift.push_back(drift_t(0,0));drift.push_back(drift_t(-50,-50));
#include <iostream>
#include <deque>
using namespace std;
class drift_t{ //It works
public:
int _drift;
int _immediateDrift;
drift_t() : _drift(0), _immediateDrift(0) {}
drift_t(int d, int expected) : _drift(d), _immediateDrift(expected) {}
drift_t(const drift_t& ro) : _drift(ro._drift), _immediateDrift(ro._immediateDrift) {}
drift_t& operator = (const drift_t& ro) { this->_drift = ro._drift; this->_immediateDrift = ro._immediateDrift; return *this; }
} ;//*/
int main() {
/*class drift_t{ //It doesn't works
public:
int _drift;
int _immediateDrift;
drift_t() : _drift(0), _immediateDrift(0) {}
drift_t(int d, int expected) : _drift(d), _immediateDrift(expected) {}
drift_t(const drift_t& ro) : _drift(ro._drift), _immediateDrift(ro._immediateDrift) {}
drift_t& operator = (const drift_t& ro) { this->_drift = ro._drift; this->_immediateDrift = ro._immediateDrift; return *this; }
} ;//*/
std::deque<drift_t> drift; drift.push_back(drift_t(0,0));drift.push_back(drift_t(-50,-50));
return 0;
}

Answer 1

Isn't the error the one that the compiler says it is? You can't use the local class for that template initialization.
Try compiling with -std=c++11 as I believe it relaxes on that.