C++基礎 學習筆記四：多載之函式多載

什么是函式多載

在C++中允許在同一作用域內宣告幾個功能類似的同名函式，也就是說用同一個函式完成不同的功能，多載函式是靜態多型性的體現，

函式多載的特點

1. 形式引數（指引數的個數、型別或者順序）必須不同，函式回傳值型別可以相同也可不同，
2. 匹配函式時并不區分const，參考&，但是const與*或&結合組成復合運算子時會進行區分，下面會進行代碼演示，
3. 避免了命名空間的污染

函式多載的實作原理

編譯程式時編譯器會對函式的原始名稱進行名稱修飾，經過修飾得到的名稱來表示函式，

函式多載的使用例子

#include<iostream>

using namespace std;

class Printer
{
	private:
		int inkVolume;
		char printerType;
	public:
		Printer():inkVolume(0),printerType('Z')
			{cout << "print by none-arg function" <<endl;}
			
		Printer(int vol):inkVolume(vol),printerType('Z')
			{cout << "print by 1-arg function" <<endl;}
			
		Printer(int vol, char type):inkVolume(vol),printerType(type)
			{cout << "print by 2-arg function" <<endl;}
			
		//void print(int value){cout << value << " print by function #1" <<endl;}//#1
		
		void print (int value) const {cout << value << " print by const function #2" <<endl;}//#2
		
		void print(int &value){cout << value  << " print by function #3" <<endl;}//#3
		
		void print(const int &value){cout << value  << " print by function #4" <<endl;}//#4
		
		void print(int &&value){cout << value  << " print by function #5" <<endl;}//#5
		
		//int print(int value){cout << value  << " print by function #6" <<endl;return 0;}//#6僅回傳值不同，編譯不通過
		
		//void print(const int value){cout << value  << " print by function #7" <<endl;}//#7
		
		//void print(int value, int value2 = 1){cout << value << value2  << " print by function #8" <<endl;}//#8默認引數在后 
			
		void print(float value){cout << value  << " print by function #9" <<endl;}//#9
		
		void print(char value){cout << value  << " print by function #10" <<endl;}//#10
		
		void print(char* value){cout << *value  << " print by function #11" <<endl;}//#11
		
		void print(const char* value){cout << *value  << " print by function #12" <<endl;}//#12
		
		//void print(char* const value){cout << value  << " print by function #13" <<endl;}//#13
};

int main()
{
	Printer printer1;
	Printer printer2(123);
	const Printer printer3(123,'A');
	
	int intValue = https://www.cnblogs.com/realZhaZhaHui/p/123;
	const int c_intValue = 1234;
	float floatValue = 1.1;
	char charValue ='A';
	char* p_charValue = https://www.cnblogs.com/realZhaZhaHui/p/new char('B');
	const char* cp_charValue = https://www.cnblogs.com/realZhaZhaHui/p/new char('C');
	
	
	//printer1.print(1);//1 是 立即數常量 可以呼叫#1，#4，#5 ，#2（當且僅當僅存在#2時） 
	printer3.print(1);//只呼叫 #2
	printer1.print(intValue);//#3 
	printer1.print(c_intValue);//#4 
	printer1.print(1+1);//#5 
	printer1.print(floatValue);//#9
	printer1.print(charValue);//#10 
	printer1.print(p_charValue);//#11
	printer1.print(cp_charValue);//#12
	
    return 0;
}
/* 運行結果為： 
print by none-arg function
print by 1-arg function
print by 2-arg function
1 print by const function #2
123 print by function #3
1234 print by function #4
2 print by function #5
1.1 print by function #9
A print by function #10
B print by function #11
C print by function #12

--------------------------------
Process exited after 0.09048 seconds with return value 0
請按任意鍵繼續. . .
*/

代碼分析

1. int value 和 const int value沒有區別，作為引數時都不會改變實參的值，不可多載，
2. char *value和const char *value是有區別的，前者指向一個字串變數，后者指向一個字串常量，可多載，
3. char *value和char const *value沒有區別，前者為字符指標變數，后者為字符指標常量，作為引數時都不會改變實參的值，不可多載，
4. int &value和const int &value是有區別的，前者指向一個整型變數，后者指向一個整型常量，可多載，
5. int &&value&&表示右值參考

標籤：C++

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