In file included from lbfgs.cpp:29:
./common.h:216:18: error: class member cannot be redeclared
  string_buffer& operator<<(size_t _n)             { _UITOA(_n); }
                 ^
./common.h:214:18: note: previous definition is here
  string_buffer& operator<<(unsigned int _n)       { _UITOA(_n); }
                 ^