Code (C++)

#include <map>
#include <string>

std::map<int, std::string> myMap;

// the setup function runs once when you press reset or power the board
void setup() {
    while (!Serial) {}

    myMap.emplace(1, "Hello");
    myMap.emplace(2, "STL");

    Serial.println(myMap[1].c_str()); // Hello
    Serial.println(myMap[2].c_str()); // STL
}

// the loop function runs over and over again until power down or reset
void loop() {
 
} 

Code

Compiling debug version of 'Sketch1' for 'Teensy 3.2 / 3.1'

Sketch1.cpp.o: In function std::_Rb_tree_iterator<std::pair<int const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::operator--()

Error linking for board Teensy 3.2 / 3.1
stl_tree.h:220: undefined reference to std  _Rb_tree_decrement(std  _Rb_tree_node_base*)
Debug build failed for project 'Sketch1'

Sketch1.cpp.o: In function std::_Rb_tree<int, std::pair<int const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::_Select1st<std::pair<int const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, std::less<int>, std::allocator<std::pair<int const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >::_M_insert_node(std::_Rb_tree_node_base*, std::_Rb_tree_node_base*, std::_Rb_tree_node<std::pair<int const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >*)
stl_tree.h:2105: undefined reference to std  _Rb_tree_insert_and_rebalance(bool, std  _Rb_tree_node_base*, std  _Rb_tree_node_base*, std  _Rb_tree_node_base&)

Sketch1.cpp.o: In function void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_construct<char const*>(char const*, char const*, std::forward_iterator_tag)
basic_string.tcc:219: undefined reference to std  __cxx11  basic_string<char, std  char_traits<char>, std  allocator<char> >  _M_create(unsigned int&, unsigned int)
basic_string.tcc:212: undefined reference to std  __throw_logic_error(char const*)

Sketch1.cpp.o: In function std::_Rb_tree_iterator<std::pair<int const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::operator--()
stl_tree.h:220: undefined reference to std  _Rb_tree_decrement(std  _Rb_tree_node_base*)

Sketch1.cpp.o: In function std::_Rb_tree_iterator<std::pair<int const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::operator++()
stl_tree.h:205: undefined reference to std  _Rb_tree_increment(std  _Rb_tree_node_base*)

collect2.exe*: error: ld returned 1 exit status