C++初学者教程 - cplusplus.com

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"这是一个针对初学者的C++教程，由Juan Soulié撰写，最后更新于2007年6月，可在cplusplus.com上找到。该在线版本会不断修订，可能包含修正和更改。" C++是一种强大的、通用的编程语言，它在软件开发领域占据着重要的地位。对于初学者来说，C++可能会显得有些复杂，因为它结合了面向过程和面向对象的编程概念。本教程旨在帮助新手理解并掌握C++的基础知识。教程内容通常会包括以下几个方面： 1. **基础语法**：C++的基础语法类似于C语言，包括变量声明、数据类型（如int, char, float等）、运算符、流程控制语句（如if-else, switch, for, while循环）等。 2. **函数**：C++中的函数用于组织代码，它们可以接收参数并返回值。学习如何定义和调用函数是C++学习的重要部分。 3. **指针**：C++的指针是其强大特性之一，它们可以存储内存地址，允许直接操作内存。理解指针的概念和操作是C++编程的关键。 4. **类和对象**：C++是面向对象的语言，通过定义类来封装数据和方法，创建对象进行实例化。学习如何设计和使用类是C++的核心。 5. **构造函数和析构函数**：构造函数用于初始化类的对象，而析构函数则在对象生命周期结束时执行，通常用于清理资源。 6. **继承和多态**：继承允许一个类（子类）继承另一个类（父类）的属性和方法，多态则使得不同的对象能对同一条消息做出不同的响应，增强了代码的灵活性和可扩展性。 7. **模板和泛型编程**：C++模板允许创建泛型函数和类，提高代码的复用性，适用于不同的数据类型。 8. **异常处理**：C++提供了一种机制来捕获和处理程序运行时的错误，异常处理确保程序在遇到问题时能优雅地恢复或终止。 9. **标准库**：C++标准库提供了大量的功能，如输入/输出流（iostream），容器（如vector, list, map等），算法（如排序、搜索等），以及其他实用工具。 10. **STL（Standard Template Library）**：STL是C++的一个重要组成部分，它包括容器、迭代器、算法和函数对象，极大地提高了编程效率。学习C++需要时间和实践，但随着深入，你将能够利用它的强大功能构建高效、可维护的软件系统。在阅读教程时，建议边学边练，编写实际的代码以加深理解。同时，注意遵循良好的编程习惯，例如编写清晰的注释、使用合适的命名规则和避免不必要的复杂性。遵循教程的指导，并且不断地进行项目实践，是成为一名熟练的C++程序员的有效途径。

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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