问c++11结构初始化编译错误

EN

struct SS {int a; int s;};

int main ()
{
   vector<SS> v;
   v.push_back(SS{1, 2});
}

struct SS {int a = 0; int s = 2;};

In function ‘int main()’:
error: no matching function for call to ‘SS::SS(<brace-enclosed initializer list>)’
     v.push_back(SS{1, 2});
                        ^
note: candidates are:
note: constexpr SS::SS()
 struct SS {int a = 0; int s = 2;};
        ^
note:   candidate expects 0 arguments, 2 provided
note: constexpr SS::SS(const SS&)
note:   candidate expects 1 argument, 2 provided
note: constexpr SS::SS(SS&&)
note:   candidate expects 1 argument, 2 provided