View Compilation Error

0_0_27854110_20854.cpp: In member function 'std::vector<int> LandAndSea::howManyIslands(std::vector<std::basic_string<char> >)':
0_0_27854110_20854.cpp:25:43: error: 'memset' was not declared in this scope
 #define CLEAR(a, b) memset(a, b, sizeof(a)) 
                                           ^
0_0_27854110_20854.cpp:106:5: note: in expansion of macro 'CLEAR'
     CLEAR(B, 0); 
     ^