技術標籤：程式設計C++隨記程式設計c++

一直對C++中“ * ”、“ & ”這兩個運算子感覺很懵，心血來潮做個程式試驗試驗，加深一下對其的理解，順便做個筆記。

一、取址符“&”與引用“&”

int x = 12;    
int* p = &x;    //定義int*型別變數並初始化，指標變數*p指向x的地址，p的值為x的地址值
cout << "p: " << p << endl;
cout << "*p: " << *p << endl;
 

顯然，上面這段程式碼中p的值為x的地址值，即&x的值；而*p的值為x的值：12

//function1-a
void function1(int* p) {
	int x = 12;
	p = &x;
	cout << "p: " << p << endl;
	cout << "*p: " << *p << endl;
}
int main() {
	int* a = new int;
	int b = 1;
	*a = b;
	cout << "a:" << a << endl;
	cout << "*a:" << *a << endl;
	function1(a);
	cout << "a:" << a << endl;
	cout << "*a:" << *a << endl;
	delete a;
	system("pause");
}
 

執行結果如下：

//function1-b
void function1(int* p) {
	int x = 12;
	p = &x;
	cout << "p: " << p << endl;
	cout << "*p: " << *p << endl;
}
int main() {
	int b = 1;
	cout << "&b:" << &b << endl;
	cout << "b:" << b << endl;
	function1(&b);
	cout << "&b:" << &b << endl;
	cout << "b:" << b << endl;
	system("pause");
}
 

執行結果如下：

//function2
void function2(int* &p) {
	int x = 12;
	p = &x;
	cout << "p: " << p << endl;
	cout << "*p: " << *p << endl;
}int main() {
	int* a = new int;
	int b = 1;
	*a = b;
	cout << "a:" << a << endl;
	cout << "*a:" << *a << endl;
	function2(a);
	cout << "a:" << a << endl;
	cout << "*a:" << *a << endl;
	delete a;
	system("pause");
}

執行結果如下：

可以看出，當引數是“ *& ”型別時，這是C++中的一種型別，其引數本質上還是引用型別，是(type)*型別的引用。以function2中int* &p為例，p是int*型別的引用引數，因此在呼叫函式時引數型別必須為int*型，按程式中的定義，似function2(b)這樣書寫是錯誤的。

二、傳參，繼續理解“*&”

//function3
void swap1(int* &p, int* &q) {
	int* temp;
	temp = p;
	p = q;
	q = temp;
	cout << "p and q: " << p << "  " << q << endl;
	cout << "*p and *q: " << *p << "  " << *q << endl;
	cout << "*&p and *&q: " << *&p << "  " << *&q << endl;
}

void swap2(int* &p, int* &q) {
	int* temp = new int;
	*temp = *p;
	*p = *q;
	*q = *temp;
	cout << "p and q: " << p << "  " << q << endl;
	cout << "*p and *q: " << *p << "  " << *q << endl;
	cout << "*&p and *&q: " << *&p << "  " << *&q << endl;
	delete temp;
}

int main() {
	int* a, * b ;
	a = new int; b = new int;
	*a = 1; *b = 2;
	cout << "a and b: " << a << "  " << b << endl;
	cout << "*a and *b: " << *a << "  " << *b << endl;
	
	swap1(a, b);

	//swap2(a, b);

	cout << "a and b: " << a << "  " << b << endl;
	cout << "*a and *b: " << *a << "  " << *b << endl;
	delete a, b;
	system("pause");
}

swap1執行結果如下：

swap2執行結果如下：

可以看出，在swap1(a,b)中，其引數p、q直接引用a、b本身，最終結果是*a與*b二者互換指向，即地址與值都互換。而swap2(a,b)中，由於在swap2函式中只進行了值的互換，對地址並無影響，所以結果中最終*a、*b的值被互換，但所指地址並未改變。