class Brass:public AcctABC
{<span style="font-family: Arial, Helvetica, sans-serif;"> </span>
private:
public:
        Brass(const std::string & s="Nullbody",long an=-1,
                double bal=0.0):AcctABC(s,an,bal){}
        virtual void Withdraw(double amt);
        virtual void ViewAcct()const;
        virtual ~Brass(){}
};
 

usebrass3.cpp:(.text._ZN5BrassC2ERKSsld[_ZN5BrassC5ERKSsld]+0x37)：對‘vtable for Brass’未定義的引用

collect2: error: ld returned 1 exit status

關鍵字‘vtable for（虛擬函式）

解決辦法查詢相關虛擬函式時候已經寫好功能函式。拿上面例子來說也就是說查詢

    virtual void Withdraw(double amt);
    virtual void ViewAcct()const;
 

   virtual void Withdraw(double amt);

void Brass::Withdraw(double amt)
{
        if(amt<0)
                cout<<"Withdrawal amount must be positive;"
                <<"withdrawal canceld.\n";
        else if(amt<=Balance())
                AcctABC::Withdraw(amt);
        else
                cout<<"Withdrawal amount of $:"<<amt<<" exceeds your balance.\n"
                        <<"Withdrawal canceled.\n";
}
 

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