View Compilation Error

0_0_29170914_20548.cpp: In member function 'void Trie::insert(char*)':
0_0_29170914_20548.cpp:39:34: error: 'strlen' was not declared in this scope
         int len = (int)strlen(buf);
                                  ^
0_0_29170914_20548.cpp: In member function 'int Trie::query(char*)':
0_0_29170914_20548.cpp:89:34: error: 'strlen' was not declared in this scope
         int len = (int)strlen(buf);
                                  ^