View Compilation Error

0_0_37671220_10005.cpp: In function 'void getnext(char*, int*)':
0_0_37671220_10005.cpp:17:25: error: 'strlen' was not declared in this scope
     int len = strlen(str);
                         ^
0_0_37671220_10005.cpp: In function 'void EXKMP(char*, char*, int*)':
0_0_37671220_10005.cpp:42:23: error: 'strlen' was not declared in this scope
     int l1 = strlen(s1), l2 = strlen(s2);
                       ^
0_0_37671220_10005.cpp:51:34: error: 'l2' was not declared in this scope
             while (p < l1 && j < l2 && s1[p] == s2[j])
                                  ^
0_0_37671220_10005.cpp: In function 'int main()':
0_0_37671220_10005.cpp:77:33: error: 'strlen' was not declared in this scope
         reverse(s1, s1+strlen(s1));
                                 ^