C++ 入门教程 C++ 备忘单

提供基本语法和方法的 C++ 快速参考备忘单。

开始

Hello.cpp

#include <iostream>

int main() {
    std::cout << "Hello QuickRef\n";
    return 0;
}

编译和运行

$ g++ hello.cpp -o hello
$ ./hello
Hello QuickRef

变量

int number = 5;       // Integer
float f = 0.95;       // Floating number
double PI = 3.14159;  // Floating number
char yes = 'Y';       // Character
std::string s = "ME"; // String (text)
bool isRight = true;  // Boolean

// Constants
const float RATE = 0.8;

int age {25};         // Since C++11
std::cout << age;     // Print 25

原始数据类型

用户输入

int num;

std::cout << "Type a number: ";
std::cin >> num;

std::cout << "You entered " << num;

交换

int a = 5, b = 10, temp;
temp = a;
a = b;
b = temp;

// Outputs: a=10, b=5
std::cout << "a=" << a << ", b=" << b;

注释

// A single one line comment in C++

/* This is a multiple line comment
   in C++ */

if 语句

if (a == 10) {
    // do something
}

请参阅：条件

for 循环

for (int i = 0; i < 10; i++) {
    std::cout << i << "\n";
}

请参阅：循环

函数

#include <iostream>
 
void hello(); // Declaring
 
int main() {  // main function
    hello();    // Calling
}
 
void hello() { // Defining
    std::cout << "Hello QuickRef!\n";
}

请参阅：函数

参考

int i = 1;
int& ri = i; // ri is a reference to i

ri = 2; // i is now changed to 2
std::cout << "i=" << i;

i = 3;   // i is now changed to 3
std::cout << "ri=" << ri;

ri并i引用相同的内存位置。

命名空间

#include <iostream>
namespace ns1 {int val(){return 5;}}
int main()
{
    std::cout << ns1::val();
}

#include <iostream>
namespace ns1 {int val(){return 5;}}
using namespace ns1;
using namespace std;
int main()
{
    cout << val(); 
}

命名空间允许名称下的全局标识符

C++ 数组

声明

int marks[3]; // Declaration
marks[0] = 92;
marks[1] = 97;
marks[2] = 98;

// Declare and initialize
int marks[3] = {92, 97, 98};
int marks[]  = {92, 97, 98};

// With empty members
int marks[3] = {92, 97};
std::cout << marks[2]; // Outputs: 0

操作

┌─────┬─────┬─────┬─────┬─────┬─────┐
| 92  | 97  | 98  | 99  | 98  | 94  |
└─────┴─────┴─────┴─────┴─────┴─────┘
   0     1     2     3     4     5

int marks[6] = {92, 97, 98, 99, 98, 94};

// Print first element
std::cout << marks[0];

// Change 2th element to 99
marks[1] = 99;

// Take input from the user
std::cin >> marks[2];

显示

char ref[5] = {'R', 'e', 'f'};

// Range based for loop
for (const int &n : ref) {
    std::cout << std::string(1, n);
}

// Traditional for loop
for (int i = 0; i < sizeof(ref); ++i) {
    std::cout << ref[i];
}

多维数组

j0   j1   j2   j3   j4   j5
   ┌────┬────┬────┬────┬────┬────┐
i0 | 1  | 2  | 3  | 4  | 5  | 6  |
   ├────┼────┼────┼────┼────┼────┤
i1 | 6  | 5  | 4  | 3  | 2  | 1  |
   └────┴────┴────┴────┴────┴────┘

int x[2][6] = {
    {1,2,3,4,5,6}, {6,5,4,3,2,1}
};
for (int i = 0; i < 2; ++i) {
    for (int j = 0; j < 6; ++j) {
        std::cout << x[i][j] << " ";
    }
}
// Outputs: 1 2 3 4 5 6 6 5 4 3 2 1

C++ 条件

if 语句

if (a == 10) {
    // do something
}

int number = 16;

if (number % 2 == 0)
{
    std::cout << "even";
}
else
{
    std::cout << "odd";
}

// Outputs: even

Else if 语句

int score = 99;
if (score == 100) {
    std::cout << "Superb";
}
else if (score >= 90) {
    std::cout << "Excellent";
}
else if (score >= 80) {
    std::cout << "Very Good";
}
else if (score >= 70) {
    std::cout << "Good";
}
else if (score >= 60)
    std::cout << "OK";
else
    std::cout << "What?";

运算符

关系运算符

赋值运算符

逻辑运算符

位运算符

三元运算符

┌── True ──┐
Result = Condition ? Exp1 : Exp2;
           └───── False ─────┘

int x = 3, y = 5, max;
max = (x > y) ? x : y;

// Outputs: 5
std::cout << max << std::endl;

int x = 3, y = 5, max;
if (x > y) {
    max = x;
} else {
    max = y;
}
// Outputs: 5
std::cout << max << std::endl;

Switch 语句

int num = 2;
switch (num) {
    case 0:
        std::cout << "Zero";
        break;
    case 1:
        std::cout << "One";
        break;
    case 2:
        std::cout << "Two";
        break;
    case 3:
        std::cout << "Three";
        break;
    default:
        std::cout << "What?";
        break;
}

C++ 循环

While

int i = 0;
while (i < 6) {
    std::cout << i++;
}

// Outputs: 012345

Do-while

int i = 1;
do {
    std::cout << i++;
} while (i <= 5);

// Outputs: 12345

Continue 语句

for (int i = 0; i < 10; i++) {
    if (i % 2 == 0) {
        continue;
    }
    std::cout << i;
} // Outputs: 13579

无限循环

while (true) { // true or 1
    std::cout << "infinite loop";
}

for (;;) {
    std::cout << "infinite loop";
}

for(int i = 1; i > 0; i++) {
    std::cout << "infinite loop";
}

for_each (从 C++11 版本开始)

#include <iostream>

void print(int num)
{
    std::cout << num << std::endl;
}

int main()
{
    int arr[4] = {1, 2, 3, 4 };
    std::for_each(arr, arr + 4, print);
    return 0;
}

Range-based (从 C++11 版本开始)

int num_array[] = {1, 2, 3, 4, 5};
for (int n : num_array) {
    std::cout << n << " ";
}
// Outputs: 1 2 3 4 5

std::string hello = "QuickRef.ME";
for (char c: hello)
{
    std::cout << c << " ";
}
// Outputs: Q u i c k R e f . M E

Break 语句

int password, times = 0;
while (password != 1234) {
    if (times++ >= 3) {
        std::cout << "Locked!\n";
        break;
    }
    std::cout << "Password: ";
    std::cin >> password; // input
}

几种变体

for (int i = 0, j = 2; i < 3; i++, j--){
    std::cout << "i=" << i << ",";
    std::cout << "j=" << j << ";";
}
// Outputs: i=0,j=2;i=1,j=1;i=2,j=0;

C++ 函数

参数和返回

#include <iostream>

int add(int a, int b) {
    return a + b;  
}

int main() {
    std::cout << add(10, 20); 
}

add是一个接受 2 个整数并返回整数的函数

Overloading 超载

void fun(string a, string b) {
    std::cout << a + " " + b;
}
void fun(string a) {
    std::cout << a;
}
void fun(int a) {
    std::cout << a;
}

内置函数

#include <iostream>
#include <cmath> // import library
 
int main() {
    // sqrt() is from cmath
    std::cout << sqrt(9);
}

C++ 预处理器

预处理器

• if
• elif
• else
• endif
• ifdef
• ifndef
• define
• undef
• include
• line
• error
• pragma
• defined
• __has_include
• __has_cpp_attribute
• export
• import
• module

Includes 包括

#include "iostream"
#include <iostream>

Defines 定义

#define FOO
#define FOO "hello"

#undef FOO

If 如果

#ifdef DEBUG
  console.log('hi');
#elif defined VERBOSE
  ...
#else
  ...
#endif

Error 错误

#if VERSION == 2.0
  #error Unsupported
  #warning Not really supported
#endif

Macro 宏

#define DEG(x) ((x) * 57.29)

Token concat 令牌连接

#define DST(name) name##_s name##_t
DST(object);   #=> object_s object_t;

Stringification 字符串化

#define STR(name) #name
char * a = STR(object);   #=> char * a = "object";

file and line 文件和行

#define LOG(msg) console.log(__FILE__, __LINE__, msg)
#=> console.log("file.txt", 3, "hey")

其他

转义序列

关键词

• alignas

• alignof

• and

• and_eq

• asm

• atomic_cancel

• atomic_commit

• atomic_noexcept

• auto

• bitand

• bitor

• bool

• break

• case

• catch

• char

• char8_t

• char16_t

• char32_t

• class

• compl

• concept

• const

• consteval

• constexpr

• constinit

• const_cast

• continue

• co_await

• co_return

• co_yield

• decltype

• default

• delete

• do

• double

• dynamic_cast

• else

• enum

• explicit

• export

• extern

• false

• float

• for

• friend

• goto

• if

• inline

• int

• long

• mutable

• namespace

• new

• noexcept

• not

• not_eq

• nullptr

• operator

• or

• or_eq

• private

• protected

• public

• reflexpr

• register

• reinterpret_cast

• requires

• return

• short

• signed

• sizeof

• static

• static_assert

• static_cast

• struct

• switch

• synchronized

• template

• this

• thread_local

• throw

• true

• try

• typedef

• typeid

• typename

• union

• unsigned

• using

• virtual

• void

• volatile

• wchar_t

• while

• xor

• xor_eq

• final

• override

• transaction_safe

• transaction_safe_dynamic

另见

• C++ 信息图表和备忘录(hackingcpp.com)
• C++ 参考(cppreference.com)
• C++ 语言教程(cplusplus.com)