C++编程语言入门教程

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"C++ Language Tutorial" 是一个由Juan Soulié编写的在线教程，主要针对C++编程语言的基础知识。该教程最后更新于2007年6月，可在c++reference.com上找到最新版本。内容包括C++的各个方面，如语法、类、对象、模板等，并且网站会不断进行修订和完善。 C++是一门强大的面向对象编程语言，由Bjarne Stroustrup在C语言的基础上发展而来，增加了类、继承、多态等特性。本教程旨在帮助初学者理解C++的基础概念，逐步掌握编程技巧。教程涵盖了以下主题： 1. **基本语法**：包括变量、数据类型、运算符、流程控制（如if语句、循环）等，这些都是任何编程语言的基础。 2. **函数**：C++中的函数用于组织代码，实现特定功能。教程将解释如何定义、调用和传递参数。 3. **类与对象**：这是C++的核心特性，类是数据和操作数据的方法的集合，对象是类的实例。教程会深入讲解如何创建和使用类。 4. **构造器与析构器**：构造器用于初始化对象，而析构器则在对象生命周期结束时执行清理工作。这些特殊函数在管理对象资源时至关重要。 5. **内存管理**：C++允许直接管理内存，包括动态内存分配和释放。理解指针和引用的概念也是C++学习的重点。 6. **继承与多态**：通过继承，一个类可以继承另一个类的属性和方法，多态则是面向对象编程的重要特性，允许不同类型的对象对同一消息做出不同的响应。 7. **模板**：C++的模板机制允许编写泛型代码，增强了代码的重用性，不论是函数模板还是类模板，都是提高效率的有效工具。 8. **异常处理**：C++提供了异常处理机制，用于在程序运行期间处理错误情况，确保程序的健壮性。 9. **输入/输出（I/O）系统**：C++标准库中的iostream库提供了方便的输入输出操作，如cin和cout，以及文件流的处理。 10. **标准库**：C++的标准库提供了大量的预定义类型和函数，如容器（如vector和list）、算法和字符串操作等，极大地丰富了编程可能性。这个教程强调实践，鼓励读者通过编写和运行代码来加深理解。同时，它提醒读者尊重版权，未经c++reference.com明确书面许可，不得复制、分发或以任何形式修改文档内容，也不得在其他网站或电子检索系统中存储和传输。学习C++不仅需要理解其语法和概念，还要通过不断练习来提升编程技能。此教程是学习C++的宝贵资源，适合初学者入门，也对有一定经验的开发者有所启发。

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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