C++编程速查指南

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"C++ Quick Syntax Reference" 是一本关于C++编程语言的速查手册，主要涵盖C++的基础语法和重要特性。C++是一种通用的多范式编程语言，它是C语言的扩展，支持面向对象编程、运算符重载、多重继承以及异常处理等特性。C++的开发始于1979年，尽管被认为是传统的编程语言，但它在软件行业中仍然广泛应用，被用于操作系统、嵌入式软件、桌面应用和游戏等各个领域。相比于新出现的语言，C++程序可能更复杂，开发周期较长，但提供对硬件的高级和低级抽象，让程序员有更大的控制权。C++设计时考虑了多种编程风格的支持，如过程式、面向对象和泛型编程，给予程序员极大的自由度。本书使用的编译器是Microsoft C++编译器，但还提到了其他常见的编译器，如Borland、Intel和GNU C++编译器。尽管C++在1998年已经标准化，但这些编译器在支持的特性上仍略有不同。书中如果涉及到特定于Microsoft编译器的内容，会特别指出。书籍内容涵盖了从入门到进阶的多个章节，包括： 1. "Hello World"：介绍基本的程序编写和运行。 2. "Compile and Run"：讲解如何编译和运行C++程序。 3. "Variables"：讨论变量的声明和使用。 4. "Operators"：涵盖各种运算符的用法。 5. "Pointers"：深入理解指针及其操作。 6. "References"：解释引用的概念和应用。 7. "Arrays"：介绍数组的创建和操作。 8. "String"：讨论字符串的处理。 9. "Conditionals"：讲述条件语句的使用。 10. "Loops"：介绍循环结构。 11. "Functions"：讲解函数的定义和调用。 12. "Class"：介绍类的定义和对象的创建。 13. "Constructor"：探讨构造函数的作用。 14. "Inheritance"：讲解类的继承机制。 15. "Overriding"：介绍方法的覆盖。 16. "Access Levels"：讨论访问权限控制。 17. "Static"：讲述静态成员的用法。 18. "Enum"：介绍枚举类型。 19. "Struct and Union"：讨论结构体和联合体的区别与使用。 20. "Operator Overloading"：深入探讨运算符重载。 21. "Custom Conversions"：讲解自定义类型转换。 22. "Namespaces"：介绍命名空间的使用。 23. "Constants"：讨论常量的声明和作用。这本书旨在帮助读者快速查阅C++的关键语法和概念，无论你是初学者还是经验丰富的程序员，都能从中受益。通过深入理解和实践这些章节中的内容，你将能够熟练掌握C++编程的核心要素，并能有效地编写和调试代码。

CHAPTER 4 ■ OPERATORs

x += 5; // x = x+5;

x -= 5; // x = x-5;

x *= 5; // x = x*5;

x /= 5; // x = x/5;

x %= 5; // x = x%5;

Increment and decrement operators

Another common operation is to increment or decrement a variable by one. This can be

simplified with the increment (++) and decrement (--) operators.

x++; // x = x+1;

x--; // x = x-1;

Both of these can be used either before or after a variable.

x++; // post-increment

x--; // post-decrement

++x; // pre-increment

--x; // pre-decrement

The result on the variable is the same whichever is used. The difference is that the

post-operator returns the original value before it changes the variable, while the

pre-operator changes the variable first and then returns the value.

x = 5; y = x++; // y=5, x=6

x = 5; y = ++x; // y=6, x=6

Comparison operators

The comparison operators compare two values and return either true or false. They

are mainly used to specify conditions, which are expressions that evaluate to either true

or false.

bool x = (2 == 3); // false // equal to

x = (2 != 3); // true // not equal to

x = (2 > 3); // false // greater than

x = (2 < 3); // true // less than

x = (2 >= 3); // false // greater than or equal to

x = (2 <= 3); // true // less than or equal to

Logical operators

The logical operators are often used together with the comparison operators. Logical and

(&&) evaluates to true if both the left and right sides are true, and logical or (||) is true if

either the left or right side is true. For inverting a Boolean result there is the logical not (!)

CHAPTER 5 ■ PoinTERs

If a second pointer is created and assigned the value of the first pointer it will then

get a copy of the first pointer’s memory address.

int* p2 = p; // copy of p (copies address stored in p)

Pointing to a pointer

Sometimes it can be useful to have a pointer that can point to another pointer. This is done

by declaring a pointer with two asterisks and then assigning it the address of the pointer

that it will reference. This way when the address stored in the first pointer changes, the

second pointer can follow that change.

int** r = &p; // pointer to p (assigns address of p)

Referencing the second pointer now gives the address of the first pointer.

Dereferencing the second pointer gives the address of the variable and dereferencing it

again gives the value of the variable.

std::cout << "Address of p: " << r; // ex. 0017FF28

std::cout << "Address of i: " << *r; // ex. 0017FF1C

std::cout << "Value of i: " << **r; // 20

Dynamic allocation

One of the main usages of pointers is to allocate memory during run-time – so called

dynamic allocation. In the examples so far, the programs have only had as much memory

available as has been declared for the variables at compile-time. This is referred to as

static allocation. If any additional memory is needed at run-time, the new operator has

to be used. This operator allows for dynamic allocation of memory, which can only be

accessed through pointers. The new operator takes either a primitive data type or an

object as its argument, and it will return a pointer to the allocated memory.

int* d = new int; // dynamic allocation

An important thing to know about dynamic allocation is that the allocated memory

will not be released like the rest of the program memory when it is no longer required.

Instead, it has to be manually released with the delete keyword. This allows you to

control the lifetime of a dynamically allocated object, but it also means that you are

responsible for deleting it once it is no longer needed. Forgetting to delete memory that

has been allocated with the new keyword will give the program memory leaks, because

that memory will stay allocated until the program shuts down.

delete d; // release allocated memory

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