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 ~ 2 31 -1 float 4字节不适用 double 8 字节不适用 char 1 字节 -128 ~ 127 bool 1 字节 true / false void 不适用不适用 wchar_t 2 或 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 < b a 小于 b a > b a 更大 b a <= b a 小于或等于 b a >= b a 大于或等于 b 赋值运算符 a += b 又名 a = a + b a -= b 又名 a = a - b a *= b 又名 a = a * b a /= b 又名 a = a / b a %= b 又名 a = a % b 逻辑运算符 exp1 && 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 & 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 << b 二进制左移 a >> 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  \n 换行 \r 返回  \t 水平标签  \v 垂直标签 \\ 反斜杠  \' 单引号  \" 双引号  \? 问号 \0 空字符  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)

C++备忘单

include <iostream>

include <iostream>

include <iostream>

include <iostream>

include <iostream>

include <iostream>

include <iostream>

include <cmath> // import library

include "iostream"

include <iostream>

define FOO

define FOO "hello"

undef FOO

ifdef DEBUG

elif defined VERBOSE

else

endif

if VERSION == 2.0

error Unsupported

warning Not really supported

endif

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

define DST(name) name##_s name##_t

define STR(name) #name

define LOG(msg) console.log(FILE, LINE, msg)

=> console.log("file.txt", 3, "hey")