如果A是基類，B是A的派生類，那麼B將繼承A的資料和函式。例如：

class A
{
public:
 void Func1(void);
 void Func2(void);
};

class B:public A
{
public:
 void Func3(void);
 void Func4(void);
};

void main()
{
 B b;
 b.Func1(); //B從A繼承了函式Func1
 b.Func2(); //B從A繼承了函式Func2
 b.Func3();
 b.Func4();
 return;
}

上面的程式碼執行後將顯示如下的錯誤資訊：

error LNK2001: unresolved external symbol "public: void __thiscall B::Func4(void)" (

[email protected]@@QAEXXZ)
error LNK2001: unresolved external symbol "public: void __thiscall B::Func3(void)" ([email protected]@@QAEXXZ)
error LNK2001: unresolved external symbol "public: void __thiscall A::Func2(void)" ([email protected]@@QAEXXZ)
 error LNK2001: unresolved external symbol "public: void __thiscall A::Func1(void)" (

[email protected]@@QAEXXZ)
Debug/繼承.exe : fatal error LNK1120: 4 unresolved externals

原因是聲明瞭Func1-4這4個函式，卻沒有定義他們

只需將程式改為：

class A
{
public:
 void Func1(void){};
 void Func2(void){};
};

class B:public A
{
public:
 void Func3(void){};
 void Func4(void){};
};

void main()
{
 B b;
 b.Func1(); //B從A繼承了函式Func1
 b.Func2(); //B從A繼承了函式Func2
 b.Func3();
 b.Func4();
 return;
}