Part0. Introduction

Chapter 1: Getting started

This chapter introduces most of the basic elements of C++: types, variables, expressions, statements, and functions. Along the way, we’ll briefly explain how to compile and execute a program.

• Writing a Simple C++ Program
• A First Look at Input/Output
• A Word about Comments
• Flow of Control
• Introducing Classes
• The Bookstore Program
• Chapter Summary
• Defined Terms

1.1. Writing a Simple C++ Program

和Java一样，C++必须有一个main函数。main函数和一般的函数除了方法名，其余部分基本相同。 Different compilers use different suffix conventions; the most common include .cc, .cxx, .cpp, .cp, and .C。本例将文件名后缀为 .cc，将上面那个方法保存至 prog1.cc文件，

prog1.cc ```cpp int main() {   return 0; } ```

1.1.1. Compiling and Executing Our Program

使用命令行编译：

# 默认参数
$ g++ prog1.cc
    => a.out
# 指定文件名
$ g++ -o prog1 prog1.cc
    => prog1

运行：

$ ./a.out
# 或者
$ ./prog1

1.2. A First Look at Input/Output

I/O 操作相关的库叫做iosteam，分别是：istream 和 ostream，并有一些内置对象， 所有标准卡的命名空间都是 std，使用 :: (operator) 进行调用：

• istream
  • cin (读作 see-in)
• ostream
  • cout (读作 see-out)
  • cerr (读作 see-err)
  • clog (读作 see-log)
  • endl

范例：

prog2.cc

#include <iostream>     // 文件头，引用iostream库
int main() {
    std::cout << "Enter two numbers:" << std::endl; // 链式操作，等价于
    // std::cout << "Enter two numbers:";
    // std::cout << std::endl; // endl 叫做 manipulator，进行flush操作
    int v1 = 0, v2 = 0;
    std::cin >> v1 >> v2;   // 接收两个参数，分别赋值到 v1 和 v2，等价于
    // std::cin >> v1;
    // std::cin >> v2;
    std::cout << "The sum of " << v1 << " and " << v2
    << " is " << v1 + v2 << std::endl;
    return 0;
}

1.3. A Word about Comments

• 单行注释：//
• 多行注释：/* */

1.4. Flow of Control

流程控制

1.4.1. The while Statement

while 语法结构，和Java一样：

while (condition)
    statement

范例：

prog3.cc ```cpp #include <iostream> int main() {
int sum = 0, val = 1;
// keep executing the while as long as val is less than or equal to 10
while (val <= 10) {
    sum += val; // assigns sum + val to sum
    ++val; // add 1 to val
}
std::cout << "Sum of 1 to 10 inclusive is "
    << sum << std::endl;
return 0; } ```

1.4.2. The for Statement

while 语法结构，和Java一样：

for (init; condition; operate)
    statement

范例：

prog4.cc ```cpp #include <iostream> int main() {
int sum = 0;
// sum values from 1 through 10 inclusive
for (int val = 1; val <= 10; ++val)
    sum += val; // equivalent to sum = sum + val
std::cout << "Sum of 1 to 10 inclusive by For loop is "
    << sum << std::endl;
return 0; } ```

1.4.3. Reading an Unknown Number of Inputs

先看范例：

prog5.cc ```cpp #include <iostream> int main() {
int sum = 0, value = 0;
// read until end-of-file, calculating a running total of all values read
while (std::cin >> value)
    sum += value; // equivalent to sum = sum + value
std::cout << "Sum is: " << sum << std::endl;
return 0; } ```

上述代码中，std::cin >> value 的返回值是一个iostream，那么对I/O对象进行test的时候，规则如何呢？ 在本范例中，因为使用value进行输入参数的接收，那么当输入的参数是int类型的时候，test为true；当输入的 参数不是int类型的时候，test为false。或者使用 end of file 来表示输入的结束，此时test也为false。 while检测到false之后，就会跳出循环，继续下面代码的运行。

Q：并不会抛异常……

1.4.4. The if Statement

和Java无差啦……

范例：

prog6.cc ```cpp #include <iostream> int main() {
// currVal is the number we're counting; we'll read new values into val
int currVal = 0, val = 0;
// read first number and ensure that we have data to process
if (std::cin >> currVal) {
    int cnt = 1; // store the count for the current value we're processing
    while (std::cin >> val) { // read the remaining numbers
        if (val == currVal) // if the values are the same
        ++cnt; // add 1 to cnt
        else { // otherwise, print the count for the previous value
            std::cout << currVal << " occurs "
                << cnt << " times" << std::endl;
            currVal = val; // remember the new value
            cnt = 1; // reset the counter
        }
    } // while loop ends here
    // remember to print the count for the last value in the file
    std::cout << currVal << " occurs "
        << cnt << " times" << std::endl;
} // outermost if statement ends here
return 0; } ```

# Input
42 42 42 42 42 55 55 62 100 100 100 done

# Output
42 occurs 5 times
55 occurs 2 times
62 occurs 1 times
100 occurs 3 times

1.5. Introducing Classes

类作为头文件 (header file) 引入，一般以 .h 作为后缀，或者 .H, .hpp, .hxx 作为后缀。 在C++标准库中，甚至没有后缀，编译器并不在乎这些后缀，但有些IDE可能在乎。

1.5.1. The Sales_item Class

定义一个 Sales_item 类，实现如下：

Sales_item.h ```cpp #ifndef SALESITEM_H #define SALESITEM_H #include <iostream> #include <string>

class Sales_item { public: Sales_item(const std::string &book):isbn(book),units_sold(0),revenue(0.0){} Sales_item(std::istream &is){ is » *this;} friend std::istream& operator»(std::istream &,Sales_item &); friend std::ostream& operator«(std::ostream &,const Sales_item &); public: Sales_item & operator+=(const Sales_item&); public: double avg_price() const; bool same_isbn(const Sales_item &rhs)const { return isbn == rhs.isbn; } Sales_item():units_sold(0),revenue(0.0){} public: std::string isbn; unsigned units_sold; double revenue; };

using std::istream; using std::ostream; Sales_item operator+(const Sales_item &,const Sales_item &); inline bool operator==(const Sales_item &lhs,const Sales_item &rhs) { return lhs.units_sold == rhs.units_sold && lhs.revenue == rhs.revenue && lhs.same_isbn(rhs); } inline bool operator!=(const Sales_item &lhs,const Sales_item &rhs) { return !(lhs == rhs); }

inline Sales_item & Sales_item::operator +=(const Sales_item &rhs) { units_sold += rhs.units_sold; revenue += rhs.revenue; return *this; } inline Sales_item operator+(const Sales_item &lhs,const Sales_item &rhs) { Sales_item ret(lhs); ret += rhs; return ret; } inline istream& operator»(istream &in,Sales_item &s) { double price; in » s.isbn » s.units_sold » price; if(in) s.revenue = s.units_sold * price; else s = Sales_item(); return in; } inline ostream& operator«(ostream &out,const Sales_item &s) { out « s.isbn « “t” «s.units_sold « “t” « s.revenue « “t” « s.avg_price(); return out; } inline double Sales_item::avg_price() const { if(units_sold) return revenue/units_sold; else return 0; } #endif

下面看一些操作范例：

    prog7.cc
```cpp
#include <iostream>
#include "Sales_item.h"
int main() {
    Sales_item book;
    // read ISBN, number of copies sold, and sales price
    std::cin >> book;
    // write ISBN, number of copies sold, total revenue, and average price
    std::cout << book << std::endl;
    return 0;
}

对于标准库的引用，使用 #include <iostream> 尖括号包裹， 对于自定义的类的引用，使用的 #include "Sales_item.h" 双引号包裹。

# Input
0-201-70353-X 4 24.99

# Output
0-201-70353-X   4       99.96   24.99

再来一个范例：

prog8.cc ```cpp #include <iostream> #include "Sales_item.h" int main() {
Sales_item book;
// read ISBN, number of copies sold, and sales price
std::cin >> book;
// write ISBN, number of copies sold, total revenue, and average price
std::cout << book << std::endl;
return 0; } ```

# Input
0-201-78345-X 3 20.00
0-201-78345-X 2 25.00

# Output
0-201-78345-X   5       110     22

1.5.2. A First Look at Member Functions

先上代码：

prog9.cc ```cpp #include <iostream> #include "Sales_item.h" int main() {
Sales_item item1, item2;
std::cin >> item1 >> item2;
// first check that item1 and item2 represent the same book
if (item1.isbn() == item2.isbn()) {
    std::cout << item1 + item2 << std::endl;
    return 0; // indicate success
} else {
    std::cerr << "Data must refer to same ISBN"
        << std::endl;
    return -1; // indicate failure
} } ```

代码 item1.isbn() == item2.isbn() 中就引用了一个叫做 isbn 的 member function。 A member function is a function that is defined as part of a class. Member functions are sometimes referred to as methods. 作为类的一部分，有时候作为method使用？ method 和 function有啥子区别？

1.6. The Bookstore Program

Part1: The Basics

Chapter2. Variables and Basic Types

Chapter3. Strings, Vectors, and Arrays

Chapter4. Expressions

Chapter5. Statements

Chapter6. Functions

Chapter7. Classes

Chapter8. The IO Library

Part2: The C++ Library

Chapter9. Sequential Containers

Chapter10. Generic Algorithms

Chapter11. Associative Containers

Chapter12. Dynamic Memory

Part3: Tools for Class Authors

Chapter13. Copy Control

Chapter14. Overloaded Operations andConversions

Chapter15. Object-Oriented Programming

Chapter16. Templates and GenericProgramming

Part4: Advanced Topics

Chapter17. Specialized Library Facilities

Chapter18. Tools for Large Programs

Chapter19. Specialized Tools andTechniques

参考资料

TODO

• 编译环境和配置：win，linux，mac

• g++ 和 gcc 区别，是指不同的编译器？

• C++ Primer (5th Edition)