foo.cpp:2:1: error: '__gnu_cxx' does not name a type
 __gnu_cxx::crope List;
 ^
foo.cpp: In function 'int main()':
foo.cpp:21:13: error: 'List' was not declared in this scope
             List.insert(now,s);
             ^
foo.cpp:26:13: error: 'List' was not declared in this scope
             List.erase(now,k);
             ^
foo.cpp:31:13: error: 'List' was not declared in this scope
             List.copy(now,k,s);
             ^