C++备忘单

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

                                数据类型

尺寸

范围

int

4字节

-2 31 ~&nbsp;2 31 -1

float

4字节

不适用

double

8 字节

不适用

char

1 字节

-128 ~&nbsp;127

bool

1 字节

true / false

void

不适用

不适用

wchar_t

2&nbsp;或&nbsp;4 个字节

1 个宽字符

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

                                a == b

a 等于 b

a != b

a 不等于 b

a &lt; b

a 小于 b

a &gt; b

a 更大 b

a &lt;= b

a 小于或等于 b

a &gt;= b

a 大于或等于 b

赋值运算符

a += b

又名&nbsp;a = a + b

a -= b

又名&nbsp;a = a - b

a *= b

又名&nbsp;a = a * b

a /= b

又名&nbsp;a = a / b

a %= b

又名&nbsp;a = a % b

逻辑运算符

exp1 &amp;&amp; exp2

两者都是真的(AND)

exp1 || exp2

要么为真(或)

!exp

exp是假的(不是)

位运算符

a &amp; b

二进制与

a | b

二进制或

a ^ b

二进制异或

a ~ b

二进制补码

a &lt;&lt; b

二进制左移

a &gt;&gt; b

二进制右移

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&nbsp;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ifelifelseendififdefifndefdefineundefincludelineerrorpragmadefined__has_include__has_cpp_attributeexportimportmodule

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

                            ​\b​

退格

​\f​

换页&nbsp;

​\n​

换行

​\r​

返回&nbsp;

​\t​

水平标签&nbsp;

​\v​

垂直标签

​\\​

反斜杠&nbsp;

​\'​

单引号&nbsp;

​\"​

双引号&nbsp;

​\?​

问号

​\0​

空字符&nbsp;

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&nbsp;(cppreference.com)

C++ 语言教程&nbsp;(cplusplus.com)