前面章節(jié)中，我們已經(jīng)學(xué)會(huì)了將操作符重載函數(shù)聲明為類的成員函數(shù)。除此之外，還可以將操作符重載函數(shù)聲明為頂層函數(shù)。

學(xué)習(xí)將操作符重載函數(shù)聲明為類成員函數(shù)時(shí)，我們不斷強(qiáng)調(diào)二元操作符的函數(shù)參數(shù)為一個(gè)，一元操作符重載函數(shù)不需要函數(shù)參數(shù)。如果以頂層函數(shù)的形式重載操作符時(shí)，二元操作符重載函數(shù)必須有兩個(gè)參數(shù)，一元操作符重載必須有一個(gè)參數(shù)。

將操作符重載函數(shù)聲明為頂層函數(shù)時(shí)，必須至少有一個(gè)類對(duì)象參數(shù)，否則編譯器無法區(qū)分操作符是系統(tǒng)內(nèi)建的還是程序設(shè)計(jì)人員自己定義的，有了一個(gè)類對(duì)象參數(shù)之后，系統(tǒng)則會(huì)根據(jù)情況調(diào)用內(nèi)建或自定的操作符。

#include <iostream> using namespace std;class complex{public:complex();complex(double a );complex (double a, double b);double getreal() const {return real;}double getimag() const {return imag;}void setreal(double a ){real =a;}void setimag(double b){imag=b;}void display() const;private:double real;double imag;};complex::complex() {real=0.0;imag=0.0; }complex::complex(double a) {real=a;imag=0.0; }complex::complex(double a, double b) {real=a;imag=b; } //打印復(fù)數(shù)void complex::display() const {cout<<real<<"+"<<imag<<"i";}//重載加法操作符 complex operator+(const complex & A,const complex &B) {complex C;C.setreal(A.getreal()+B.getreal());C.setimag(A.getimag()+B.getimag());return C; }//重載減法操作符 complex operator-(const complex & A,const complex &B) {complex C;C.setreal(A.getreal()-B.getreal());C.setimag(A.getimag()-B.getimag());return C; } //重載乘法操作符 complex operator*(const complex & A,const complex &B) {complex C;C.setreal(A.getreal()*B.getreal()-A.getimag()*B.getimag());C.setimag(A.getreal()*B.getimag()+A.getimag()+B.getreal());return C; }//重載除法操作符complex operator/(const complex &A,const complex &B) { complex C;double square=B.getreal()*B.getreal() +B.getimag()*B.getimag();C.setreal((A.getreal()*B.getreal()+A.getimag()*B.getimag())/square); C.setimag((A.getimag() * B.getreal() - A.getreal() * B.getimag())/square); return C;}int main(){complex c1(1.0,2.0);complex c2(3.0, 4.0);complex c3;c3 = c1 + c2;cout<<"c1 + c2 = ";c3.display();cout<<endl;c3 = c1 - c2;cout<<"c1 - c2 = ";c3.display();cout<<endl;c3 = c1 * c2;cout<<"c1 * c2 = ";c3.display();cout<<endl;c3 = c1 / c2;cout<<"c1 / c2 = ";c3.display();cout<<endl;return 0;} c1 + c2 = 4+6i c1 - c2 = -2+-2i c1 * c2 = -5+9i c1 / c2 = 0.44+0.08i

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