Operator Overload

重载->，*和&的例子：

 

// 一个图书馆系统，书目记录格式如下:// "%Aauthor/0%Ttitle/0%Ppublisher/0%Ccity/0%Vvolume/0%Yyear/0/n"// 这些字段可以按任意顺序出现，若无输入值，则采取defBook定义的缺省值#include <iostream>using namespace std;// 在访问记录字段时采用以下结构struct Book{ char * raw; char * author; char * title; char * publisher; char * city; short vol; short year;};Book defBook = {"raw", "Author?", "Title?", "Publisher?", "City?", 0, 0};// 定义一个表示原始记录的类，并重载单目指针运算符，// 以便在需要时，把一个原始记录映射为Book结构class RawBook{ char * data; Book * RawToBook();public: RawBook(char * str) {data = str;} Book * operator ->(); Book & operator * (); Book * operator & ();};// 使用10个记录的简单cache以减少从RawBook到Book的映射频率static Book cache[10]; // cache memorystatic short curr; // current record in cachestatic short used; // number of used cache records// 在cache中搜索RawBook，并返回其对应的Book结构指针。// 如果这条书目不在cache中，RawBook把当前位置的书目装入缓存Book * RawBook::RawToBook(){ char * str = data; for(int i = 0; i < used; ++i)// 是否raw book已被记录？ { if(data == cache[i].raw) { return cache + i; } } curr = used < 10 ? used++ : (curr < 9 ? ++curr : 0); Book * bk = cache + curr; *bk = defBook; // 不同于bk = &defBook; bk->raw = data; for(;;) { while(*str++ != '%') ; switch(*str++) { case 'A': bk->author = str; break; case 'T': bk->title = str; break; case 'P': bk->publisher = str; break; case 'C': bk->city = str; break; case 'V': bk->vol = atoi(str); break; case 'Y': bk->year = atoi(str); break; } while(*str++ != '/0') ; if(*str == '/n') break; } return bk;}Book * RawBook::operator ->(){ return RawToBook();}Book & RawBook::operator *(){ return *RawToBook();}Book * RawBook::operator &(){ return RawToBook();}int main(){ RawBook r1("%AAdele.L/0%TLTE concepts/0%PBrooks Cols/0%CBeijing/0%Y2015/0/n"); RawBook r2("%AOpal.M/0%TLinux kernel/0%PPrentice Hall/0%V1/0%Y2016/0/n"); cout<< r1->author << ", " << r1->title << ", " << r1->publisher << ", " << r1->city << ", " << (* r1).vol << ", " << (* r1).year << "/n"; Book * bp = &r2; // note use of & cout<< bp->author << ", " << bp->title << ", " << bp->publisher << ", " << bp->city << ", " << bp->vol << ", " << bp->year << "/n"; system("PAUSE"); return 0;}

 

打印结果：

 

Adele.L, LTE concepts, Brooks Cols, Beijing, 0, 2015
Opal.M, Linux kernel, Prentice Hall, City?, 1, 2016