Accepted.

#include <iostream>
#include <cstring>

#define int long long
#define i64 long long
#define endl '\n'
#define qwq puts("fzy qwq ~");
#define rep(i, l, r) for (int i = (l); i <= (r); ++i)

using namespace std;

namespace bufIO

Complie Error.

#include <iostream>

#define int long long
#define i64 long long
#define endl '\n'
#define qwq puts("fzy qwq ~");
#define rep(i, l, r) for (int i = (l); i <= (r); ++i)

using namespace std;

#include <cstring>
namespace bufIO

/tmp/compiler_spsve8y6/src:3:18: 错误：‘long long long’对 GCC 来说太长了
    3 | #define int long long
      |                  ^~~~
/tmp/compiler_spsve8y6/src:3:13: 错误：‘long long long’对 GCC 来说太长了
    3 | #define int long long
      |             ^~~~
/tmp/compiler_spsve8y6/src:3:18: 错误：‘long long long’对 GCC 来说太长了
    3 | #define int long long
      |                  ^~~~