View Compilation Error

0_0_22848181_28599.cpp: In function 'void get_next(char*, int*)':
0_0_22848181_28599.cpp:13:24: error: 'strlen' was not declared in this scope
     int len0 = strlen(s);
                        ^
0_0_22848181_28599.cpp: In function 'int kmp(char*, char*, int*, int)':
0_0_22848181_28599.cpp:32:24: error: 'strlen' was not declared in this scope
     int lena = strlen(a);
                        ^
0_0_22848181_28599.cpp: In function 'int main()':
0_0_22848181_28599.cpp:62:29: error: 'strlen' was not declared in this scope
         int len1 = strlen(s1);
                             ^