在C ++中，我們可以使運算符適用於用戶定義的類。 這意味着C ++能夠為運算符提供數據類型的特殊含義，這種能力稱為運算符重載。
例如，我們可以在像String這樣的類中重載運算符'+'，這樣我們就可以通過使用+來連接兩個字符串。
其它示例中算術運算符可以重載的的類是復數，小數，大整數等。
運算符重載的語法格式：
Return_Type classname :: operator op(Argument list)
{
Function Body
}
在上面的語法中，Return_Type是要返回給另一個對象的值類型，operator op是運算符是關鍵字的函數，op是要重載的運算符。
運算符函數必須是非靜態（成員函數）或友元函數。
運算符重載可以通過三種方法完成，它們是
1) 重載一元運算符。
2) 重載二元運算符。
3) 使用友元函數重載二元運算符。
以下是定義運算符函數的一些條件/規則：
l 在非靜態函數的情況下，二元運算符應該只有一個參數，而一元不應該有一個參數。
l 在友元函數的情況下，二元運算符應該只有兩個參數，而一元應該只有一個參數。
l 如果實現了運算符重載，則所有類成員對象都應該是公共的。
運算符函數和普通函數有什么區別？
運算符函數與普通函數相同。 唯一的區別是，運算符函數的名稱始終是operator關鍵字，后跟運算符符號，並且在使用相應的運算符時調用運算符函數。
除了極個別的運算符外，大部分運算符都可以被重載。
以下是可以重載的運算符列表：
以下是不可以重載的運算符列表：
為什么（點），::，？：和sizeof不可以重載看這里解釋。
關於運算符重載的重要方面：
1）為了使操作符重載起作用，其中一個操作數必須是用戶定義的類對象。
2）賦值運算符：編譯器自動為每個類創建一個默認賦值運算符。 默認賦值運算符確實將右側的所有成員分配到左側，並且在大多數情況下都能正常工作（此行為與復制構造函數相同）。
3）轉換運算符：我們還可以編寫可用於將一種類型轉換為另一種類型的轉換運算符。重載的轉換運算符必須是成員方法。 其他運算符可以是成員方法或全局方法。
4）任何可以用單個參數調用的構造函數都可以用作轉換構造函數，這意味着它也可以用於隱式轉換為正在構造的類。
綜合例子：學習測試，僅供參考！
OperatorOverloadingClass.h
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#ifndef
OPERATOROVERLOADINGCLASS_H #define OPERATOROVERLOADINGCLASS_H #include <iostream> using namespace std; const int SIZE = 10 ; class OperatorOverloadingClass { public : OperatorOverloadingClass(); OperatorOverloadingClass( const int &number, const float &fnumber); // 賦值運算符 void operator = ( const OperatorOverloadingClass &obj) { m_number = obj.m_number; } // 函數調用()運算符 OperatorOverloadingClass operator ()( int a, int b, int c) { OperatorOverloadingClass D; // just put random calculation D.m_number = a + b + c; return D; } void print(); /* OperatorOverloading */ // 算術運算符 // + OperatorOverloadingClass operator + ( const OperatorOverloadingClass &obj); // - OperatorOverloadingClass operator - ( const OperatorOverloadingClass &obj); // * OperatorOverloadingClass operator * ( const OperatorOverloadingClass &obj); // / OperatorOverloadingClass operator / ( const OperatorOverloadingClass &obj); // % OperatorOverloadingClass operator % ( const OperatorOverloadingClass &obj); // 關系運算符 // < bool operator < ( const OperatorOverloadingClass &obj); // > bool operator > ( const OperatorOverloadingClass &obj); // <= bool operator <= ( const OperatorOverloadingClass &obj); // >= bool operator >= ( const OperatorOverloadingClass &obj); // == bool operator == ( const OperatorOverloadingClass &obj); // != bool operator != ( const OperatorOverloadingClass &obj); // 位運算符 // ^ OperatorOverloadingClass operator ^ ( const OperatorOverloadingClass &obj); // & OperatorOverloadingClass operator & ( const OperatorOverloadingClass &obj); // | OperatorOverloadingClass operator | ( const OperatorOverloadingClass &obj); // 邏輯運算符 // && bool operator && ( const OperatorOverloadingClass &obj); // || bool operator || ( const OperatorOverloadingClass &obj); // 取地址運算符& int * operator &() { return & this ->m_number; } // 內存操作運算符* int operator *(OperatorOverloadingClass *obj) { return obj->m_number; } // 輸入輸出運算符 // << friend ostream & operator <<(ostream &output, const OperatorOverloadingClass &obj ) { output << "number : " << obj.m_number; return output; } // >> friend istream & operator >>(istream &input, OperatorOverloadingClass &obj) { input >> obj.m_number; return input; } // 自增自減運算符 // ++i OperatorOverloadingClass operator ++(); // i++ OperatorOverloadingClass operator ++( int ); // --i OperatorOverloadingClass operator --(); // i-- OperatorOverloadingClass operator --( int ); // 數組成員訪問運算符[] int & operator []( int i) { if ( i > SIZE ) { cout << "Index out of bounds" << endl; // return first element. return arr[ 0 ]; } return arr[i]; } // 類成員訪問運算符-> // https://www.cnblogs.com/codingmengmeng/p/9064702.html // 復合賦值運算符：+=、-=、*=、/=、%=、<<=、>>=、^=、&=、|= void operator += ( const OperatorOverloadingClass &obj) { m_number += obj.m_number; } // 其余類似 // 重載類型轉換 operator int () { return m_number; } operator float () { return m_fnumber; } // new delete void * operator new (size_t size); void operator delete ( void *p); void * operator new [](size_t size); void operator delete []( void *p, size_t size); private : int m_number; float m_fnumber; int arr[SIZE]; }; #endif // OPERATOROVERLOADINGCLASS_H |
OperatorOverloadingClass.cpp
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#include
"OperatorOverloadingClass.h"
#include <QDebug> OperatorOverloadingClass::OperatorOverloadingClass() { m_number = 0 ; m_fnumber = 0 . 0 ; for ( int i = 0 ; i < SIZE; i++) { arr[i] = i; } } OperatorOverloadingClass::OperatorOverloadingClass( const int &number, const float &fnumber) : m_number(number) , m_fnumber(fnumber) { for ( int i = 0 ; i < SIZE; i++) { arr[i] = i; } } void OperatorOverloadingClass::print() { qDebug() << "m_number =" << m_number; } OperatorOverloadingClass OperatorOverloadingClass:: operator +( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = this ->m_number + obj.m_number; return out; } OperatorOverloadingClass OperatorOverloadingClass:: operator -( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = this ->m_number - obj.m_number; return out; } OperatorOverloadingClass OperatorOverloadingClass:: operator *( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = this ->m_number * obj.m_number; return out; } OperatorOverloadingClass OperatorOverloadingClass:: operator /( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = this ->m_number / obj.m_number; return out; } OperatorOverloadingClass OperatorOverloadingClass:: operator %( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = this ->m_number % obj.m_number; return out; } OperatorOverloadingClass OperatorOverloadingClass:: operator ^( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = ( this ->m_number) ^ (obj.m_number); return out; } OperatorOverloadingClass OperatorOverloadingClass:: operator &( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = ( this ->m_number) & (obj.m_number); return out; } OperatorOverloadingClass OperatorOverloadingClass:: operator |( const OperatorOverloadingClass &obj) { OperatorOverloadingClass out; out.m_number = ( this ->m_number) | (obj.m_number); return out; } bool OperatorOverloadingClass:: operator &&( const OperatorOverloadingClass &obj) { return ( this ->m_number) && (obj.m_number); } bool OperatorOverloadingClass:: operator ||( const OperatorOverloadingClass &obj) { return ( this ->m_number) || (obj.m_number); } bool OperatorOverloadingClass:: operator <( const OperatorOverloadingClass &obj) { if (m_number < obj.m_number) { return true ; } return false ; } bool OperatorOverloadingClass:: operator >( const OperatorOverloadingClass &obj) { if (m_number > obj.m_number) { return true ; } return false ; } bool OperatorOverloadingClass:: operator <=( const OperatorOverloadingClass &obj) { if (m_number <= obj.m_number) { return true ; } return false ; } bool OperatorOverloadingClass:: operator >=( const OperatorOverloadingClass &obj) { if (m_number >= obj.m_number) { return true ; } return false ; } bool OperatorOverloadingClass:: operator ==( const OperatorOverloadingClass &obj) { if (m_number == obj.m_number) { return true ; } return false ; } bool OperatorOverloadingClass:: operator !=( const OperatorOverloadingClass &obj) { if (m_number != obj.m_number) { return true ; } return false ; } // overloaded prefix ++ operator OperatorOverloadingClass OperatorOverloadingClass:: operator ++ () { ++m_number; // increment this object return OperatorOverloadingClass(m_number, 0 . 0 ); } // overloaded postfix ++ operator OperatorOverloadingClass OperatorOverloadingClass:: operator ++( int ) { // save the orignal value OperatorOverloadingClass T(m_number, 0 . 0 ); // increment this object ++m_number; // return old original value return T; } // overloaded prefix -- operator OperatorOverloadingClass OperatorOverloadingClass:: operator -- () { --m_number; // increment this object return OperatorOverloadingClass(m_number, 0 . 0 ); } // overloaded postfix -- operator OperatorOverloadingClass OperatorOverloadingClass:: operator --( int ) { // save the orignal value OperatorOverloadingClass T(m_number, 0 . 0 ); // increment this object --m_number; // return old original value return T; } void *OperatorOverloadingClass:: operator new (size_t size) { return malloc(size); } void OperatorOverloadingClass:: operator delete ( void *p) { free(p); } inline void *OperatorOverloadingClass:: operator new [](size_t size) { OperatorOverloadingClass *p = (OperatorOverloadingClass *)malloc(size); return p; } inline void OperatorOverloadingClass:: operator delete []( void *p, size_t size) { free(p); } |