View Compilation Error

0_0_21538682_13140.cpp: In function 'void getnext(char*, int*)':
0_0_21538682_13140.cpp:12:26: error: 'strlen' was not declared in this scope
    while(j<=strlen(substr))
                          ^
0_0_21538682_13140.cpp: In function 'int kmp(char*, char*)':
0_0_21538682_13140.cpp:38:22: error: 'strlen' was not declared in this scope
   if(j==strlen(substr))
                      ^