C++入门注意事项
一、编程环境搭建
（一）编译器选择与安装
1. GCC
* 简介：GCC（GNU Compiler Collection）是一个功能强大且广泛使用的开源编译器套件。它支持多种编程语言，包括 C++。在 Linux 系统中，它常常是默认的编译器，可通过包管理器轻松安装，如在 Ubuntu 系统中使用sudo apt-get install g++命令。
* 编译命令示例：对于简单的 C++源文件（例如hello.cpp），使用g++ hello.cpp -o hello命令进行编译。其中-o选项指定输出的可执行文件名。GCC 提供了丰富的编译选项，比如-g用于生成调试信息，-O系列选项用于优化代码（如-O2）。
2. Clang
* 特点：Clang 是一个 C、C++、Objective - C 和 Objective - C++ 编程语言的编译器前端。它以快速的编译速度、高质量的诊断信息和良好的内存安全性而受到欢迎。与 GCC 类似，可用于多种操作系统。
* 使用示例：使用clang++ source.cpp -o output来编译 C源文件。它对 C标准的支持较为先进，并且与一些现代开发工具（如 LLVM 相关的分析工具）集成良好。
3. Visual C++ 编译器（MSVC）
* 适用平台：这是 Windows 平台下开发 C++的重要选择，它是 Visual Studio 集成开发环境（IDE）的一部分。
* 项目配置要点：在 Visual Studio 中创建 C++项目时，需要注意选择合适的项目类型（如控制台应用程序、Windows 应用程序等）。在项目属性中，可以配置编译模式（Debug 模式方便调试，Release 模式用于生成优化后的可执行文件）、目标平台（x86、x64 等）以及其他编译选项，这些设置会影响程序的性能、大小和兼容性。
（二）集成开发环境（IDE）的使用
1. Visual Studio
* 功能特性：功能丰富全面，适合初学者和专业开发者。它提供了直观的图形化界面，方便创建、编辑和管理 C++项目。例如，通过模板可以快速创建不同类型的 C ++项目。其代码编辑功能强大，有自动补全、语法检查和智能提示，有助于提高编程效率。
* 调试功能：内置的调试器是 Visual Studio 的一大亮点。在调试过程中，可以设置断点、查看变量的值和类型、观察调用栈信息等。这对于查找程序中的逻辑错误和运行时错误非常有帮助。例如，当程序出现异常时，可以通过调试器定位到出错的代码行。
2. Code::Blocks
* 优势：这是一款跨平台的开源 IDE，支持多种编译器，包括 GCC 和 Clang。它的界面简洁，易于初学者上手。对于简单的 C++学习和开发项目来说，是一个不错的选择。
* 项目管理：在 Code::Blocks 中，可以方便地创建和管理 C++项目。可以手动配置编译器路径和编译选项，也可以使用默认设置进行快速开发。
3. Eclipse（CDT）
* 特点与配置：Eclipse 是一款著名的开源 IDE，通过安装 C/C开发工具（CDT）插件来支持 C开发。它在代码编辑、项目管理方面有出色的表现，并且支持与代码版本控制系统（如 Git）集成。在使用时，需要正确配置 C++编译器路径和相关环境变量，确保项目能够顺利编译和运行。
二、C++基础语法
（一）数据类型
1. 基本数据类型
* 整型：C++ 中的整型类型有int、short、long、long long等。不同整型类型的字节数和取值范围不同，例如在 32 位系统中，int通常占 4 个字节，取值范围是 -2147483648 到 2147483647。在选择整型类型时，要根据实际需要的数值范围来确定，避免数据溢出。
* 浮点型：包括float和double。float精度较低，一般占 4 个字节，double精度更高，占 8 个字节。在涉及到对精度要求较高的计算（如科学计算、金融计算）时，应优先选择double。
* 字符型：char类型用于存储单个字符，占 1 个字节。字符在内存中是以 ASCII 码值存储的，可以进行算术运算（如字符的大小写转换）。
* 布尔型：bool类型只有两个值true和false，用于表示逻辑判断的结果。在条件语句和逻辑运算中经常使用。
2. 复合数据类型
* 数组：数组是一组相同类型元素的有序集合。例如int arr[5];定义了一个包含 5 个整型元素的数组。数组下标从 0 开始，访问数组元素时要确保下标不越界，否则可能导致程序崩溃或出现不可预测的结果。
* 结构体：结构体可以将不同类型的数据组合在一起。例如：
可以通过Student stu;定义结构体变量，然后使用stu.age = 18;等方式访问结构体成员。
- 联合体：联合体中所有成员共享同一块内存空间。例如：
使用时要注意数据覆盖问题，因为对一个成员赋值可能会改变其他成员的值。
- 枚举：枚举类型用于定义一组有名字的常量。例如：
这里RED、GREEN、BLUE的值默认从 0 开始依次递增，可以手动指定枚举常量的值。
3. 指针和引用
- 指针：指针是一个变量，其值为另一个变量的地址。例如int *p;定义了一个指向整型的指针。指针在使用前要初始化，可以将其指向一个已存在的变量（如int num = 10; p = #），或者初始化为nullptr（C++11 及以后）或NULL（早期版本兼容）。指针的解引用操作（如*p）可以访问指针所指向的变量的值，但要确保指针指向有效的内存地址，避免出现野指针。
- 引用：引用是一个变量的别名。例如int num = 10; int &ref = num;，ref就是num的引用。引用必须在定义时初始化，并且在其生命周期内不能重新绑定到其他变量。引用在函数参数传递和函数返回值等场景中有重要应用。
（二）变量和常量
1. 变量的定义和初始化
* 定义规则：变量在使用前必须先定义，指定其数据类型和名称。例如double price;定义了一个双精度浮点型变量price。可以在定义变量的同时进行初始化，如int count = 0;。初始化可以使用常量、表达式或其他已初始化的变量。
* 作用域：变量有不同的作用域，包括局部作用域（在函数内部定义的变量，函数执行结束后变量被销毁）、全局作用域（在所有函数外部定义的变量，可以在整个程序中访问，但要注意避免滥用，以免影响程序的可读性和可维护性）等。在不同的作用域内可以定义同名变量，但它们是相互独立的。
2. 常量的定义和使用
* const关键字：使用const关键字可以定义常量，例如const int MAX_SIZE = 100;。一旦定义了常量，就不能再对其进行修改。常量在程序中用于表示那些在运行过程中不应该改变的值，如数组大小限制、数学常数等。
* constexpr（C++11 及以后）：constexpr关键字用于定义编译期常量表达式。例如constexpr int square(int x) { return x * x; }，这样的函数可以在编译时计算出结果，并且可以用于定义数组大小等需要常量表达式的地方。
（三）运算符和表达式
1. 算术运算符
* 基本运算：包括加（+）、减（-）、乘（*）、除（/）和取模（%）。整数除法和浮点数除法有区别，当两个操作数都是整数时，除法运算结果取整（如5 / 2结果为 2）；当至少有一个操作数是浮点数时，得到浮点数结果。取模运算符%要求两个操作数都为整数，且除数不能为 0，用于计算余数。
2. 关系运算符和逻辑运算符
* 关系运算符：有大于（>）、小于（<）、大于等于（>=）、小于等于（<=）、等于（==）和不等于（!=）。在使用等于运算符（==）时要特别注意与赋值运算符（=）区分，避免逻辑错误。例如，if (a == 5)是正确的条件判断，而if (a = 5)会将 5 赋值给a，并且条件判断结果恒为真（非 0 值表示真）。
* 逻辑运算符：包括逻辑与（&&）、逻辑或（||）和逻辑非（!）。逻辑与和逻辑或有短路求值特性，即对于&&，当第一个操作数为假时，不会计算第二个操作数；对于||，当第一个操作数为真时，不会计算第二个操作数。例如(a > 5) && (b < 10)，如果a > 5为假，则不会再判断b < 10。
3. 位运算符
* 位运算操作：位运算符用于对整数的二进制位进行操作，包括按位与（&）、按位或（|）、按位异或（^）、取反（~）、左移（<<）和右移（>>）。例如，a << 2表示将a的二进制位向左移动 2 位，相当于乘以 4（对于无符号整数）。在使用左移和右移运算符时，要注意数据类型的取值范围，避免溢出问题，特别是对于有符号整数的右移操作，要考虑符号位的处理。
（四）控制结构
1. 顺序结构：顺序结构是程序最基本的执行方式，按照语句的书写顺序依次执行。在编写代码时，要保证语句顺序符合逻辑，例如变量的初始化应该在使用之前，避免出现未定义行为。
2. 选择结构
* if - else语句：用于根据条件判断执行不同的代码块。例如：
可以有多个else if分支来处理多种情况，如：
在switch - case语句中，case后面的值必须是常量表达式，并且每个case分支通常需要加上break语句，否则会出现执行流程穿透到下一个case分支的情况。
3. 循环结构
- for循环：适用于已知循环次数的情况。例如：
其中，初始化表达式int i = 0只在循环开始时执行一次，条件表达式i < 10用于控制循环是否继续，迭代表达式i++在每次循环体执行后执行。
- while循环：根据条件判断是否继续循环。例如：
要注意循环条件的正确性，避免死循环。例如，如果condition始终为真且没有其他跳出循环的机制，就会导致死循环。
- do - while循环：先执行一次循环体，然后再判断条件。例如：
这种循环保证循环体至少会执行一次。在循环结构中，可以使用break语句跳出整个循环，使用continue语句跳过本次循环剩余的语句，直接进入下一次循环。
三、函数
（一）函数的定义和声明
1. 函数定义
* 基本结构：函数由函数头和函数体组成。函数头包括函数返回类型、函数名、参数列表，函数体是用花括号括起来的一组语句。例如：
这里int是返回类型，add是函数名，(int a, int b)是参数列表，函数体实现了两个整数相加并返回结果的功能。在定义函数时，要确保函数返回类型与实际返回值的类型一致，参数的类型和数量要准确无误。
2. 函数声明
- 作用与形式：函数声明用于告诉编译器函数的名称、返回类型和参数类型等信息，使编译器在调用函数时能进行类型检查。函数声明通常放在头文件或源文件的开头部分。例如：int add(int, int);是add函数的声明。通过函数声明，可以在不同的源文件中共享函数信息，提高代码的模块化和可维护性。
（二）函数参数传递
1. 值传递
* 原理与示例：值传递是将实参的值复制一份传递给形参。例如：
在值传递过程中，函数内部对形参的修改不会影响到实参。
2. 引用传递
- 使用方法与效果：引用传递是将变量的引用作为参数传递给函数。例如：
通过引用传递，函数可以直接访问和修改调用函数时传递的变量。
3. 指针传递
- 操作与注意事项：指针传递是将变量的指针作为参数传递给函数。例如：
在使用指针传递时，要注意指针的有效性，避免空指针解引用等问题。
（三）函数重载和内联函数
1. 函数重载
* 定义与规则：函数重载是指在同一个作用域内，可以有多个同名函数，它们的参数列表不同（参数个数、参数类型或者参数顺序不同）。例如：
这里有两个add函数，一个用于整型相加，一个用于双精度浮点型相加。在调用重载函数时，编译器会根据传递的参数类型和数量来选择合适的函数版本。需要注意的是，函数的返回类型不能作为重载的依据，并且重载函数之间的功能逻辑要清晰，避免混淆。
2. 内联函数
- 作用与声明：内联函数是一种特殊的函数，在编译时会将函数体的代码直接插入到调用该函数的地方，减少函数调用的开销。使用inline关键字来声明内联函数，例如：
内联函数适用于函数体较小且频繁调用的情况，但编译器并不一定会完全按照inline关键字的指示来内联函数，它会根据一些优化策略
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PRECAUTIONS FOR C++ BEGINNERS
I. SETUP OF PROGRAMMING ENVIRONMENT
(I) SELECTION AND INSTALLATION OF COMPILERS
1. GCC
* Introduction: GCC (GNU Compiler Collection) is a powerful and widely used open-source compiler suite. It supports multiple programming languages, including C++. In Linux systems, it is often the default compiler and can be easily installed via package managers. For example, in the Ubuntu
system, you can use the command "sudo apt-get install g++" to install it.
* Example of Compilation Commands: For a simple C++ source file (such as "hello.cpp"), you can use the command "g++ hello.cpp -o hello" to compile it. The "-o" option is used to specify the name of the output executable file. GCC provides a rich set of compilation options, such as "-g" for
generating debugging information and the "-O" series options for optimizing the code (e.g., "-O2").
2. Clang
* Features: Clang is a compiler front end for programming languages such as C, C++, Objective - C, and Objective - C++. It is popular for its fast compilation speed, high-quality diagnostic information, and good memory safety. Similar to GCC, it can be used on multiple operating systems.
* Usage Example: Use the command "clang++ source.cpp -o output" to compile a C++ source file. It has more advanced support for C++ standards and integrates well with some modern development tools (such as analysis tools related to LLVM).
3. Visual C++ Compiler (MSVC)
* Applicable Platform: This is an important choice for developing C++ on the Windows platform. It is part of the Visual Studio Integrated Development Environment (IDE).
* Key Points of Project Configuration: When creating a C++ project in Visual Studio, you need to pay attention to selecting the appropriate project type (such as console application, Windows application, etc.). In the project properties, you can configure the compilation mode (Debug mode for
easy debugging, Release mode for generating optimized executable files), the target platform (x86, x64, etc.), and other compilation options. These settings will affect the performance, size, and compatibility of the program.
(II) USAGE OF INTEGRATED DEVELOPMENT ENVIRONMENTS (IDE)
1. Visual Studio
* Functional Features: It has rich and comprehensive functions, suitable for both beginners and professional developers. It provides an intuitive graphical interface, making it convenient to create, edit, and manage C++ projects. For example, you can quickly create different types of C++
projects through templates. Its code editing functionality is powerful, with features like auto-completion, syntax checking, and intelligent hints, which help improve programming efficiency.
* Debugging Function: The built-in debugger is a highlight of Visual Studio. During the debugging process, you can set breakpoints, view the values and types of variables, and observe the call stack information. This is very helpful for finding logical errors and runtime errors in the program.
For example, when an exception occurs in the program, you can use the debugger to locate the line of code where the error occurred.
2. Code::Blocks
* Advantages: It is a cross-platform open-source IDE that supports multiple compilers, including GCC and Clang. Its interface is simple and easy for beginners to get started with. It is a good choice for simple C++ learning and development projects.
* Project Management: In Code::Blocks, you can conveniently create and manage C++ projects. You can manually configure the compiler path and compilation options, or you can use the default settings for quick development.
3. Eclipse (CDT)
* Features and Configuration: Eclipse is a famous open-source IDE. By installing the C/C++ Development Tools (CDT) plugin, it supports C++ development. It performs well in code editing and project management and also supports integration with code version control systems (such as Git). When
using it, you need to correctly configure the C++ compiler path and related environment variables to ensure that the project can be compiled and run smoothly.
II. BASIC SYNTAX OF C++
(I) DATA TYPES
1. Basic Data Types
* Integer Types: Integer types in C++ include "int", "short", "long", "long long", etc. Different integer types have different byte sizes and value ranges. For example, in a 32-bit system, "int" usually occupies 4 bytes, with a value range from -2147483648 to 2147483647. When choosing an integer
type, you should determine it according to the actual required value range to avoid data overflow.
* Floating-Point Types: They include "float" and "double". "float" has lower precision and generally occupies 4 bytes, while "double" has higher precision and occupies 8 bytes. When it comes to calculations that require higher precision (such as scientific calculations and financial
calculations), "double" should be preferred.
* Character Type: The "char" type is used to store a single character and occupies 1 byte. Characters are stored in memory as ASCII code values and can be subjected to arithmetic operations (such as converting the case of a character).
* Boolean Type: The "bool" type has only two values, "true" and "false", and is used to represent the result of logical judgments. It is often used in conditional statements and logical operations.
2. Composite Data Types
* Arrays: An array is an ordered collection of elements of the same type. For example, "int arr[5];" defines an array containing 5 integer elements. Array subscripts start from 0, and when accessing array elements, you must ensure that the subscript does not exceed the bounds, otherwise it may
cause the program to crash or produce unpredictable results.
* Structures: Structures can combine different types of data together. For example:
You can define a structure variable like "Student stu;" and then access the members of the structure using "stu.age = 18;", etc.
- Unions: All members in a union share the same memory space. For example:
When using it, you should pay attention to the data overwrite problem because assigning a value to one member may change the values of other members.
- Enums: The enumeration type is used to define a set of named constants. For example:
Here, the values of "RED", "GREEN", and "BLUE" default to incrementing from 0 in sequence, and you can manually specify the values of enumeration constants.
3. Pointers and References
* Pointers: A pointer is a variable whose value is the address of another variable. For example, "int *p;" defines a pointer to an integer. Before using a pointer, it must be initialized. It can be pointed to an existing variable (such as "int num = 10; p = #") or initialized to "nullptr" (in
C++11 and later) or "NULL" (for compatibility with earlier versions). The dereference operation of a pointer (such as "*p") can access the value of the variable pointed to by the pointer, but you must ensure that the pointer points to a valid memory address to avoid wild pointers.
* References: A reference is an alias of a variable. For example, "int num = 10; int &ref = num;" where "ref" is a reference to "num". A reference must be initialized when defined, and it cannot be rebound to other variables during its lifetime. References have important applications in
scenarios such as function parameter passing and function return values.
(II) VARIABLES AND CONSTANTS
1. Definition and Initialization of Variables
* Definition Rules: Variables must be defined before use, specifying their data type and name. For example, "double price;" defines a double-precision floating-point variable "price". You can initialize a variable at the same time as defining it, such as "int count = 0;". Initialization can be
done using constants, expressions, or other already initialized variables.
* Scope: Variables have different scopes, including local scope (variables defined inside a function are destroyed after the function execution ends) and global scope (variables defined outside all functions can be accessed throughout the program, but you should be careful to avoid overusing
them to avoid affecting the readability and maintainability of the program). You can define variables with the same name in different scopes, but they are independent of each other.
2. Definition and Use of Constants
* The "const" Keyword: You can define a constant using the "const" keyword. For example, "const int MAX_SIZE = 100;". Once a constant is defined, it cannot be modified. Constants are used in programs to represent values that should not change during the running process, such as array size
limitations and mathematical constants.
* The "constexpr" (C++11 and later): The "constexpr" keyword is used to define compile-time constant expressions. For example, "constexpr int square(int x) { return x * x; }". Such a function can calculate the result at compile time and can be used to define array sizes and other places that
require constant expressions.
(III) OPERATORS AND EXPRESSIONS
1. Arithmetic Operators
* Basic Operations: They include addition ("+"), subtraction ("-"), multiplication ("*"), division ("/"), and modulo ("%"). There is a difference between integer division and floating-point division. When both operands are integers, the division operation results in an integer (for example, "5 /
2" results in 2); when at least one operand is a floating-point number, a floating-point result is obtained. The modulo operator "%" requires both operands to be integers and the divisor cannot be 0, and it is used to calculate the remainder.
2. Relational Operators and Logical Operators
* Relational Operators: They include greater than (">"), less than ("<"), greater than or equal to (">="), less than or equal to ("<="), equal to ("== "), and not equal to ("!="). When using the equal to operator ("=="), you should be especially careful to distinguish it from the assignment
operator ("=") to avoid logical errors. For example, "if (a == 5)" is a correct conditional judgment, while "if (a = 5)" will assign 5 to "a" and the conditional judgment result will always be true (a non-zero value represents true).
* Logical Operators: They include logical AND ("&&"), logical OR ("||"), and logical NOT ("!"). Logical AND and logical OR have short-circuit evaluation characteristics. That is, for "&&", if the first operand is false, the second operand will not be evaluated; for "||", if the first operand is
true, the second operand will not be evaluated. For example, in "(a > 5) && (b < 10)" if "a > 5" is false, then "b < 10" will not be evaluated.
3. Bit Operators
* Bitwise Operations: Bit operators are used to perform operations on the binary bits of integers, including bitwise AND ("&"), bitwise OR ("|"), bitwise XOR ("^"), bitwise NOT ("~"), left shift ("<<"), and right shift (">>"). For example, "a << 2" means shifting the binary bits of "a" to the
left by 2 positions, which is equivalent to multiplying by 4 (for unsigned integers). When using the left shift and right shift operators, you should pay attention to the value range of the data type to avoid overflow problems, especially when dealing with the right shift operation of signed
integers, you should consider the handling of the sign bit.
(IV) CONTROL STRUCTURES
1. Sequential Structure: The sequential structure is the most basic way of program execution, where statements are executed in the order they are written. When writing code, you should ensure that the order of statements is logical. For example, variables should be initialized before use to avoid
undefined behavior.
2. Selection Structures
* The "if - else" Statement: It is used to execute different code blocks according to conditional judgments. For example:
You can have multiple "else if" branches to handle multiple situations, such as:
In the "switch - case" statement, the values after "case" must be constant expressions, and each "case" branch usually requires a "break" statement, otherwise the execution flow will penetrate to the next "case" branch.
3. Loop Structures
* The "for" Loop: It is suitable for situations where the number of loop iterations is known. For example:
Here, the initialization expression "int i = 0" is executed only once at the start of the loop, the condition expression "i < 10" is used to control whether the loop continues, and the iteration expression "i++" is executed after each execution of the loop body.
- The "for" Loop: It is suitable for situations where the number of loop iterations is known. For example:
Here, the initialization expression "int i = 0" is executed only once at the start of the loop, the condition expression "i < 10" is used to control whether the loop continues, and the iteration expression "i++" is executed after each execution of the loop body.
- The "while" Loop: It determines whether to continue looping based on a condition. For example:
You should pay attention to the correctness of the loop condition to avoid infinite loops. For example, if "condition" is always true and there is no other mechanism to break out of the loop, it will result in an infinite loop.
- The "do - while" Loop: It executes the loop body once first and then judges the condition. For example:
This type of loop ensures that the loop body is executed at least once. In loop structures, you can use the "break" statement to break out of the entire loop and the "continue" statement to skip the remaining statements in the current loop iteration and directly enter the next loop iteration.
III. FUNCTIONS
(I) DEFINITION AND DECLARATION OF FUNCTIONS
1. Function Definition
* Basic Structure: A function consists of a function header and a function body. The function header includes the return type of the function, the function name, and the parameter list. The function body is a group of statements enclosed in curly braces. For example:
Here, "int" is the return type, "add" is the function name, and "(int a, int b)" is the parameter list. The function body implements the functionality of adding two integers and returning the result. When defining a function, it is necessary to ensure that the return type of the function is
consistent with the actual return value type, and the types and quantities of parameters should be accurate.
2. Function Declaration
* Function and Form: A function declaration is used to inform the compiler of the name, return type, and parameter types of a function, enabling the compiler to perform type checking when the function is called. Function declarations are usually placed at the beginning of a header file or a
source file. For example, "int add(int, int);" is the declaration of the "add" function. Through function declarations, function information can be shared among different source files, improving the modularity and maintainability of the code.
(II) FUNCTION PARAMETER PASSING
1. Value Passing
* Principle and Example: Value passing means that a copy of the value of the actual parameter is passed to the formal parameter. For example:
During the process of value passing, modifications to the formal parameter inside the function do not affect the actual parameter.
2. Reference Passing
* Usage Method and Effect: Reference passing means passing the reference of a variable as a parameter to a function. For example:
Through reference passing, the function can directly access and modify the variable passed when calling the function.
3. Pointer Passing
* Operation and Precautions: Pointer passing means passing the pointer of a variable as a parameter to a function. For example:
When using pointer passing, it is necessary to pay attention to the validity of the pointer to avoid issues such as dereferencing a null pointer.
(III) FUNCTION OVERLOADING AND INLINE FUNCTIONS
1. Function Overloading
* Definition and Rules: Function overloading means that within the same scope, there can be multiple functions with the same name, but their parameter lists are different (in terms of the number of parameters, parameter types, or parameter order). For example:
Here, there are two "add" functions, one for adding integers and the other for adding double-precision floating-point numbers. When calling an overloaded function, the compiler will select the appropriate function version based on the type and number of parameters passed. It should be noted that the
return type of a function cannot be used as a basis for overloading, and the functional logic between overloaded functions should be clear to avoid confusion.
2. Inline Functions
* Function and Declaration: An inline function is a special type of function. During compilation, the code of the function body will be directly inserted into the place where the function is called, reducing the overhead of function calls. The "inline" keyword is used to declare an inline
function. For example:
Inline functions are suitable for cases where the function body is small and the function is frequently called. However, the compiler does not necessarily follow the instructions of the "inline" keyword completely to inline the function. It will make decisions based on some optimization strategies.
