C++经典教程：在线修订版

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C++英文教程是由Juan Soulié编写的经典教材，最初修订于2007年6月，可在官方网站<http://www.cplusplus.com/doc/tutorial/>获取。该在线教程是一个持续更新的资源，旨在帮助学习者深入了解C++语言。教程包含了丰富的内容，版权属于cplusplus.com，2008年起所有权利受到保留。该教程的重要部分包括以下几个方面： 1. **版权信息与使用规定**: - 学习者必须遵守版权声明，未经cppreference.com明确书面许可，不得复制或在任何形式上重新分发教程内容，除非个人打印整篇文档或下载到本地硬盘，但必须保持内容原貌，包括版权声明。 - 任何形式的在线传播或存储都必须得到版权所有者的许可，禁止未经授权的电子检索系统使用。 2. **目录结构**: - 教程提供详细的目录，使读者能够快速找到他们感兴趣的主题，方便学习者按照逻辑顺序逐步掌握C++语言的不同概念和技术。 3. **介绍与使用指南**: - 开始部分会简要介绍C++语言，包括其历史背景、目的以及与其他编程语言的关系，以帮助读者了解学习C++的意义和目标。 - 教程可能包含一系列指导性步骤，告知读者如何最有效地利用这个在线资源，例如阅读建议、实践练习和解决常见问题的方法。 4. **深入内容**: - 教程涵盖了C++的基础知识，如数据类型、控制结构（如循环、条件语句）、函数、类和对象、模板、异常处理等核心概念。每个主题都深入浅出地讲解，并可能伴有实例代码来帮助理解。 5. **不断更新与修订**: - 鉴于C++语言的动态发展，教程的在线版本会定期更新和修正错误，确保内容的准确性和时效性。通过这个C++英文教程，学习者可以系统地学习C++语言，无论是初学者还是进阶开发者，都能从中获益匪浅。它不仅是理论知识的宝库，也是实践经验的重要参考。务必遵守使用规定，尊重作者的知识产权，以获得最佳的学习体验。

A first difference with fundamental data types is that in order to declare and use objects (variables) of this type we

need to include an additional header file in our source code: <string> and have access to the std namespace

(which we already had in all our previous programs thanks to the using namespace statement).

// my first string

#include <iostream>

#include <string>

using namespace std;

int main ()

{

string mystring = "This is a string";

cout << mystring;

return 0;

}

This is a string

As you may see in the previous example, strings can be initialized with any valid string literal just like numerical

type variables can be initialized to any valid numerical literal. Both initialization formats are valid with strings:

string mystring = "This is a string";

string mystring ("This is a string");

Strings can also perform all the other basic operations that fundamental data types can, like being declared without

an initial value and being assigned values during execution:

// my first string

#include <iostream>

#include <string>

using namespace std;

int main ()

{

string mystring;

mystring = "This is the initial string content";

cout << mystring << endl;

mystring = "This is a different string content";

cout << mystring << endl;

return 0;

}

This is the initial string content

This is a different string content

For more details on C++ strings, you can have a look at the string class reference.

Constants

Constants are expressions with a fixed value.

Literals

Literals are used to express particular values within the source code of a program. We have already used these

previously to give concrete values to variables or to express messages we wanted our programs to print out, for

example, when we wrote:

a = 5;

the 5 in this piece of code was a literal constant.

Literal constants can be divided in Integer Numerals, Floating-Point Numerals, Characters, Strings and Boolean

Values.

Integer Numerals

1776

707

-273

They are numerical constants that identify integer decimal values. Notice that to express a numerical constant we

do not have to write quotes (") nor any special character. There is no doubt that it is a constant: whenever we

write 1776 in a program, we will be referring to the value 1776.

In addition to decimal numbers (those that all of us are used to use every day) C++ allows the use as literal

constants of octal numbers (base 8) and hexadecimal numbers (base 16). If we want to express an octal number

we have to precede it with a 0 (zero character). And in order to express a hexadecimal number we have to precede

it with the characters 0x (zero, x). For example, the following literal constants are all equivalent to each other:

75 // decimal

0113 // octal

0x4b

// hexadecimal

All of these represent the same number: 75 (seventy-five) expressed as a base-10 numeral, octal numeral and

hexadecimal numeral, respectively.

Literal constants, like variables, are considered to have a specific data type. By default, integer literals are of type

int. However, we can force them to either be unsigned by appending the u character to it, or long by appending l:

75 // int

75u // unsigned int

75l // long

75ul

// unsigned long

In both cases, the suffix can be specified using either upper or lowercase letters.

Floating Point Numbers

They express numbers with decimals and/or exponents. They can include either a decimal point, an e character

(that expresses "by ten at the Xth height", where X is an integer value that follows the e character), or both a

decimal point and an e character:

3.14159 // 3.14159

6.02e23 // 6.02 x 10^23

1.6e-19 // 1.6 x 10^-19

3.0 // 3.0

These are four valid numbers with decimals expressed in C++. The first number is PI, the second one is the

number of Avogadro, the third is the electric charge of an electron (an extremely small number) -all of them

approximated- and the last one is the number three expressed as a floating-point numeric literal.

The default type for floating point literals is double. If you explicitly want to express a float or long double

numerical literal, you can use the f or l suffixes respectively:

3.14159L // long double

6.02e23f // float

Any of the letters that can be part of a floating-point numerical constant (e, f, l) can be written using either lower

or uppercase letters without any difference in their meanings.

Character and string literals

There also exist non-numerical constants, like:

'z'

'p'

"Hello world"

"How do you do?"

The first two expressions represent single character constants, and the following two represent string literals

composed of several characters. Notice that to represent a single character we enclose it between single quotes (')

and to express a string (which generally consists of more than one character) we enclose it between double quotes

(").

When writing both single character and string literals, it is necessary to put the quotation marks surrounding them

to distinguish them from possible variable identifiers or reserved keywords. Notice the difference between these

two expressions:

'x'

x alone would refer to a variable whose identifier is x, whereas 'x' (enclosed within single quotation marks) would

refer to the character constant 'x'.

Character and string literals have certain peculiarities, like the escape codes. These are special characters that are

difficult or impossible to express otherwise in the source code of a program, like newline (\n) or tab (\t). All of

them are preceded by a backslash (\). Here you have a list of some of such escape codes:

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