View Compilation Error

0_0_20547602_29650.cpp: In function 'void insert(char*, int)':
0_0_20547602_29650.cpp:26:23: error: 'strlen' was not declared in this scope
   int len = strlen(str);
                       ^
0_0_20547602_29650.cpp: In function 'std::vector<std::pair<int, int> > query(char*)':
0_0_20547602_29650.cpp:71:23: error: 'strlen' was not declared in this scope
   int len = strlen(str);
                       ^