Operator Overload

最新推荐文章于 2025-12-30 14:18:03 发布

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#cache #struct #system #linux #class #c

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本文通过一个图书馆系统的实例，展示了如何在C++中重载指向成员的指针运算符（->）、解引用运算符（*）及取地址运算符（&）。通过定义`RawBook`类来缓存并转换原始书籍数据到结构化的`Book`类型，从而实现高效的数据访问。

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 memory static short curr; // current record in cache static 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