C++學習筆記(6)----基類和派生類的構造函數和析構函數的執行順序

基類和派生類：構造函數和析構函數的執行順序

在Visual Studio中，新建控制台工程，構造類如下：

#include<iostream>
using namespace std;

class CBase {
public:
	CBase() {
		cout << "CBase():Constructor" << endl;
	}
	~CBase() {
		cout << "CBase(): Destructor" << endl;
	}
};

class CDerive :public CBase {
public:
	CDerive() {
		cout << "CDerive():Constructor" << endl;
	}
	~CDerive() {
		cout << "CDerive(): Destructor" << endl;
	}
};

對應不同的指針進行 delete 操作，結果如下：

(i)

int main(int argc, char* argv[])
{
	CBase* p = new CDerive();
	delete p;
	return 0;
}

運行結果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CBase(): Destructor

(ii)

int main(int argc, char* argv[])
{
	CDerive* pp = new CDerive();
	delete pp;
	return 0;
}

運行結果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CDerive(): Destructor
CBase(): Destructor

(iii)

int main(int argc, char* argv[])
{
	CDerive* pp = new CDerive();
	CBase * p = (CBase*)pp;
	delete p;
	return 0;
}

運行結果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CBase(): Destructor

(iv)

int main(int argc, char* argv[])
{
	CBase * p = new CDerive();
	CDerive * pp = (CDerive*)p;
	delete pp;
	return 0;
}

運行結果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CDerive(): Destructor
CBase(): Destructor

總結：
由上面的實驗結果可以看出，當 new CDerive() 時，會先運行基類的構造函數，然后再運行派生類的構造函數；
而當 delete pointer 時，編譯器只考慮 pointer 指針本身的類型而不關心 pointer 實際指向的類型，即：若 pointer 為基類指針，則只調用基類的析構函數(不管 pointer 實際指向的是基類還是派生類)；若 pointer 是派生類指針，則先調用派生類的析構函數，再調用基類的析構函數，調用順序與調用構造函數的順序相反。