View Compilation Error

0_0_26141289_20301.cpp: In member function 'void Trie::insert(char*)':
0_0_26141289_20301.cpp:18:27: error: 'strlen' was not declared in this scope
         int len=strlen(buf);
                           ^
0_0_26141289_20301.cpp: In member function 'int Trie::query(char*)':
0_0_26141289_20301.cpp:51:27: error: 'strlen' was not declared in this scope
         int len=strlen(buf);
                           ^