[問題] 有關C++Primer中文版,p461頁(12.4.4)

看板C_and_CPP (C/C++)作者easterday (....)時間12年前 (2013/08/02 13:57)推噓2(2推 0噓 6→)

留言8則, 4人參與討論串1/1

上次經過大家的幫忙,終於讓我比較了解這一節在做甚麼但是又有新的疑問了... #include <string> #include <iostream> using namespace std; class Sales_item { public: friend istream& operator>>(istream& in, Sales_item& s); std::string isbn; int unit_sold; double revenue; Sales_item(const std::string &book="") :isbn(book),unit_sold(0),revenue(0.0) {} Sales_item(istream& is); bool same_isbn(const Sales_item& that) const; }; Sales_item::Sales_item(istream& is) { is>> *this; } bool Sales_item::same_isbn(const Sales_item& that) const { return (isbn==that.isbn); } istream& operator>>(istream& in, Sales_item& s) { double price; in>> s.isbn >> s.unit_sold >> price; if (in) s.revenue= s.unit_sold * price; else s=Sales_item(); return in; } class ESales_item { public: friend istream& operator>>(istream& in, ESales_item& s); std::string isbn; int unit_sold; double revenue; explicit ESales_item(const std::string &book="") :isbn(book),unit_sold(0),revenue(0.0) {} explicit ESales_item(istream& is); bool same_isbn(const ESales_item& that) const; }; ESales_item::ESales_item(istream& is) { is>> *this; } bool ESales_item::same_isbn(const ESales_item& that) const { return (isbn==that.isbn); } istream& operator>>(istream& in, ESales_item& s) { double price; in>> s.isbn >> s.unit_sold >> price; if (in) s.revenue= s.unit_sold * price; else s=ESales_item(); return in; } int main() { Sales_item item(string("9")); string null_book = "9"; // cout << item.same_isbn("999")<<endl; //compiling err cout << item.same_isbn(null_book)<<endl; // cout<< item.same_isbn(cin)<<endl; //good ESales_item item2(string("9")); //item2.same_isbn(null_book); //compling err //item2.same_isbn(cin); //compilng err ESales_item another("9"); //explicit的功用應該是禁止隱式轉換,為什麼又把const char* ==>string了?? cout << item2.same_isbn(another) <<endl; getchar(); return 0; } explicit的功用應該是禁止隱式轉換但是為什麼又把const char*轉換成了string?? -- -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 114.38.228.150