条款9：绝不要在构造以及析构函数中调用虚函数

 1 class Transaction{
 2 public:
 3     Transaction();
 4     virtual void logTransactions()s const = 0;
 5     //...
 6 };
 7 Transaction::Transaction()
 8 {
 9     //...
10     logTransaction();
11 }
12 class BuyTransaction : public Transaction{
13 public:
14     virtual void logTransaction() const;
15     ...
16 };
17 class SellTransaction : public Transaction{
18 public:
19     virtual void logTransaction() const;
20     ...
21 };