ログインチェック

# include <iostream>
# include <time.h>

using namespace std;

/**
 * now - 現在の日時
 * time - 前回のログイン日時
 * hours - 日付更新時刻
 * timezone - タイムゾーン
 */
bool loginCheck(int now, int time, int hours, int timezone)
{
    int tz = timezone * 3600;
    int offset = -hours * 3600;
    now += tz + offset;
    now -= now % 86400;
    time += tz + offset;
    return now > time;
}

//------- test >>

int dt(char *s)
{
    struct tm tm_;
    memset(&tm_, 0, sizeof(struct tm));
    strptime(s, "%Y-%m-%d %H:%M:%S", &tm_);
    return mktime(&tm_);
}

string toString(bool b)
{
  return b ? "true" : "false";
}

int main(int argc, char *argv[]) 
{
	// loginCheck(現在の日時, 前回のログイン日時, 日付更新時刻, タイムゾーン);
    cout << toString(loginCheck(dt("2013-01-01 03:59:59"), dt("2012-12-31 03:59:59"), 4, 9)) << "\n"; // true
    cout << toString(loginCheck(dt("2013-01-01 03:59:59"), dt("2012-12-31 04:00:00"), 4, 9)) << "\n"; // false
    cout << toString(loginCheck(dt("2013-01-01 04:00:00"), dt("2012-12-31 04:00:00"), 4, 9)) << "\n"; // true
    cout << toString(loginCheck(dt("2013-01-01 00:00:00"), dt("2012-12-31 23:59:59"), 4, 9)) << "\n"; // false
    cout << toString(loginCheck(dt("2013-01-01 04:00:00"), dt("2013-01-01 04:00:00"), 4, 9)) << "\n"; // false
    cout << toString(loginCheck(dt("2013-01-01 03:59:59"), dt("2013-01-01 00:00:00"), 4, 9)) << "\n"; // false
    cout << toString(loginCheck(dt("2013-01-01 04:00:00"), dt("2013-01-01 03:59:59"), 4, 9)) << "\n"; // true
    cout << toString(loginCheck(dt("2013-01-01 04:00:00"), dt("2013-01-01 04:00:00"), 4, 9)) << "\n"; // false
    cout << toString(loginCheck(dt("2013-01-01 04:00:01"), dt("2013-01-01 04:00:00"), 4, 9)) << "\n"; // false
}