View Compilation Error

0_0_21081791_32558.cpp: In function 'void getNext()':
0_0_21081791_32558.cpp:6:21: error: 'strlen' was not declared in this scope
     int len=strlen(W);
                     ^
0_0_21081791_32558.cpp: In function 'int Kmp()':
0_0_21081791_32558.cpp:32:22: error: 'strlen' was not declared in this scope
     int len1=strlen(W);
                      ^