View Compilation Error

0_0_22132484_17723.cpp: In member function 'void Trie::insert(char*)':
0_0_22132484_17723.cpp:31:23: error: 'strlen' was not declared in this scope
   int len = strlen(buf); int now = root;
                       ^
0_0_22132484_17723.cpp: In member function 'int Trie::query(char*)':
0_0_22132484_17723.cpp:63:23: error: 'strlen' was not declared in this scope
   int len = strlen(buf); int now = root;
                       ^
0_0_22132484_17723.cpp: In function 'int main()':
0_0_22132484_17723.cpp:106:23: error: 'strlen' was not declared in this scope
    int ll = strlen(tmp);
                       ^