View Compilation Error

0_0_17435552_24703.cpp: In function 'void pre()':
0_0_17435552_24703.cpp:5:39: error: 'memset' was not declared in this scope
 #define  clr(a,b) memset(a,b,sizeof(a))
                                       ^
0_0_17435552_24703.cpp:19:2: note: in expansion of macro 'clr'
  clr(head,-1);clr(dfn,0);clr(ins,0);clr(low,0);clr(belong,0);
  ^