/in/foo.cc:24:10: error: extra qualification 'BinTree::' on member 'CreatebyPreMid' [-fpermissive]
   Node * BinTree::CreatebyPreMid(char pre[],int ipre, char mid[],int imid, int len)
          ^~~~~~~
/in/foo.cc: In constructor 'BinTree::BinTree(char*, char*)':
/in/foo.cc:20:38: error: 'strlen' was not declared in this scope
    int ipre=0, imid=0, len=strlen(pre);
                                      ^