Hi Ni Yuan, >please tell me the reasons for such error message, thank you very much! Some problems I see with the code: 1. you do not have #include <fstream>, yet you are using ofstream instance. 2. you do not have using std::ofstream. 3. you do not have using std::cout. 4. you do not have using std::endl. 5. you are missing a declaration for Path_Table. 6. you are missing a declaration for TreePattern 7. you are missing #include <cstdlib>, yet you are using the exit function It also appears that you are using a very, very, very, very old version of GCC (2.95.x). I recommend using GCC 3.4.3, so as to avoid problems and to prevent learning anachronistic idioms (which you'd have to unlearn later). HTH, --Eljay
