Compilare: user.cpp: In function ‘int main()’: user.cpp:12:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("logs.in","r",stdin); ^ user.cpp:13:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("logs.out","w",stdout); ^ user.cpp:15:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&n,&m); ^ user.cpp:17:34: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(str+1,1,23000000,stdin); ^ In file included from /usr/include/string.h:635:0, from /usr/include/c++/5/cstring:42, from /usr/include/x86_64-linux-gnu/c++/5/32/bits/stdc++.h:48, from user.cpp:1: In function ‘void* memcpy(void*, const void*, size_t)’, inlined from ‘int main()’ at user.cpp:23:36: /usr/include/bits/string3.h:53:71: warning: call to void* __builtin___memcpy_chk(void*, const void*, unsigned int, unsigned int) will always overflow destination buffer return __builtin___memcpy_chk (__dest, __src, __len, __bos0 (__dest)); ^