View Compilation Error

0_0_21631046_30301.cpp: In function 'void GetNextval()':
0_0_21631046_30301.cpp:12:22: error: 'strlen' was not declared in this scope
  int w_len = strlen(W) - 1;
                      ^
0_0_21631046_30301.cpp: In function 'int KMP()':
0_0_21631046_30301.cpp:34:22: error: 'strlen' was not declared in this scope
  int t_len = strlen(T) - 1;
                      ^