《C++ primer 5》 chapter 1.5 1.6

note

In C++ we define our own data structures by defining aclass. 

A class defines a type along with a collection ofoperations that are related to that type. 

Header file names are derived from the name of a class defined in that header. 

Header files that we write usually have a suffix of .h, but some programmers use .H, .hpp, or .hxx. 

The standard library headers typically haveno suffix at all. 

This program starts with two #include directives, one of which uses a new form. Headers from the standard library are enclosed in angle brackets (< >). Those that are not part of the library are enclosed in double quotes (" "). 

File redirect 

$ addItems outfile Assuming 

$ is the system prompt and our addition program has been compiled into an executable file named addItems.exe (or addItems on UNIX systems).

This command will read transactions from a file named infile and write its output to a file named outfile in the current directory. 

Member functions are sometimes referred to as methods.

The dot operator applies only to objects of class type. The left-hand operand must be an object of class type, and the right-hand operand must name a member of that type. The result of the dot operator is the member named by the right-hand operand. 

We call a function using the call operator (the () operator).

exercise

exercise 1.20

#include<iostream>#include"Sales_item.h"int main(){Sales_item s;while(std::cin>>s){std::cout<<s;}system("pause");return 0;}

其中用到了头文件中的

std::istream& operator>>(std::istream& in, Sales_item& s){    double price;    in >> s.bookNo >> s.units_sold >> price;    // check that the inputs succeeded    if (in)        s.revenue = s.units_sold * price;    else         s = Sales_item();  // input failed: reset object to default state    return in;}std::ostream& operator<<(std::ostream& out, const Sales_item& s){    out << s.isbn() << " " << s.units_sold << " "        << s.revenue << " " << s.avg_price();    return out;}

exercise 1.21

#include<iostream>#include"Sales_item.h"int main(){Sales_item a,b;std::cin>>a>>b;if(compareIsbn(a,b)){std::cout<<a+b<<std::endl;}else{std::cerr<<"not the same ISBN"<<std::endl;}system("pause");return 0;}

用到头文件的输入输出重载符以及

bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs) { return lhs.isbn() == rhs.isbn(); }

Sales_item operator+(const Sales_item& lhs, const Sales_item& rhs) {    Sales_item ret(lhs);  // copy (|lhs|) into a local object that we'll return    ret += rhs;           // add in the contents of (|rhs|)     return ret;           // return (|ret|) by value}

exercise 1.22

#include<iostream>#include"Sales_item.h"int main(){Sales_item tran,tran_curr,sum;std::cin>>tran;while(std::cin>>tran_curr){if(compareIsbn(tran,tran_curr)){sum = tran + tran_curr;tran = sum;}else{std::cerr<<"must be the same ISBN"<<std::endl;}}std::cout<<sum<<std::endl;system("pause");return 0;}

exercise 1.23

#include<iostream>#include"Sales_item.h"int main(){Sales_item item1,item2,item3,newItem;std::cin>>item1;while(std::cin>>newItem){if(newItem.isbn() == item1.isbn()){item1 += newItem;}else if(newItem.isbn() == item2.isbn()){item2 += newItem;}else if(newItem.isbn() == item3.isbn()){item3 += newItem;} else{if (item2.isbn() == ""){item2 = newItem;}else{item3 = newItem;}}}std::cout<<item1<<std::endl<<item2<<std::endl<<item3<<std::endl;system("pause");return 0;}

exercise 1.24

exercise 1.25