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C++ Cheat Sheet - 快速参考指南，收录常用语法、命令与实践。

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Getting Started

hello.cpp

CPP

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#include <iostream>

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

Compiling and running

SHELL

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

Variables

CPP

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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;

CPP

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

Primitive Data Types

Data Type	Size	Range
`int`	4 bytes	-2^31^ ^to^ 2^31^-1
`float`	4 bytes	N/A
`double`	8 bytes	N/A
`char`	1 byte	-128 ^to^ 127
`bool`	1 byte	true / false
`void`	N/A	N/A
`wchar_t`	2 ^or^ 4 bytes	1 wide character

{.show-header}

User Input

CPP

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int num;

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

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

Swap

CPP

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int a = 5, b = 10;
std::swap(a, b);

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

Comments

CPP

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// A single one line comment in C++

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

If statement

CPP

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

See: Conditionals

Loops

CPP

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

See: Loops

Functions

CPP

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#include <iostream>

void hello(); // Declaring

int main() {  // main function
    hello();    // Calling
}

void hello() { // Defining
    std::cout << "Hello CheatSheets!\n";
}

See: Functions

References

CPP

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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 and i refer to the same memory location.

Namespaces

CPP

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

CPP

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

Namespaces allow global identifiers under a name

C++ Arrays

Declaration

CPP

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std::array<int, 3> marks; // Definition
marks[0] = 92;
marks[1] = 97;
marks[2] = 98;

// Define and initialize
std::array<int, 3> = {92, 97, 98};

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

Manipulation

CPP

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

CPP

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std::array<int, 6> marks = {92, 97, 98, 99, 98, 94};

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

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

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

Displaying

CPP

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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];
}

Multidimensional

CPP

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

CPP

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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++ Conditionals

If Clause

CPP

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

CPP

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int number = 16;

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

// Outputs: even

Else if Statement

CPP

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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?";

Operators

Relational Operators


`a == b`	a is equal to b
`a != b`	a is NOT equal to b
`a < b`	a is less than b
`a > b`	a is greater b
`a <= b`	a is less than or equal to b
`a >= b`	a is greater or equal to b

Assignment Operators

Example	Equivalent to
`a += b`	Aka a = a + b
`a -= b`	Aka a = a - b
`a *= b`	Aka a = a * b
`a /= b`	Aka a = a / b
`a %= b`	Aka a = a % b

Logical Operators

Example	Meaning
`exp1 && exp2`	Both are true (AND)
<code>exp1 \|\| exp2</code>	Either is true (OR)
`!exp`	`exp` is false (NOT)

Bitwise Operators

Operator	Description
`a & b`	Binary AND
<code>a \| b</code>	Binary OR
`a ^ b`	Binary XOR
`~ a`	Binary One's Complement
`a << b`	Binary Shift Left
`a >> b`	Binary Shift Right

Ternary Operator

CODE

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

CPP

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

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

CPP

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

Switch Statement

CPP

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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++ Loops

While

CPP

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

// Outputs: 012345

Do-while

CPP

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

// Outputs: 12345

Continue statements

CPP

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

Infinite loop

CPP

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

CPP

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

CPP

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

for_each (Since C++11)

CPP

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#include <iostream>
#include <array>

int main()
{
    auto print = [](int num) { std::cout << num << std::endl; };

    std::array<int, 4> arr = {1, 2, 3, 4};
    std::for_each(arr.begin(), arr.end(), print);
    return 0;
}

Range-based (Since C++11)

CPP

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

CPP

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

Break statements

CPP

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

Several variations

CPP

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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++ Functions

Arguments & Returns

CPP

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#include <iostream>

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

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

add is a function taking 2 ints and returning int

Overloading

CPP

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

Built-in Functions

CPP

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#include <iostream>
#include <cmath> // import library

int main() {
    // sqrt() is from cmath
    std::cout << sqrt(9);
}

C++ Classes & Objects

Defining a Class

CPP

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class MyClass {
  public:             // Access specifier
    int myNum;        // Attribute (int variable)
    string myString;  // Attribute (string variable)
};

Creating an Object

CPP

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MyClass myObj;  // Create an object of MyClass

myObj.myNum = 15;          // Set the value of myNum to 15
myObj.myString = "Hello";  // Set the value of myString to "Hello"

cout << myObj.myNum << endl;         // Output 15
cout << myObj.myString << endl;      // Output "Hello"

Constructors

CPP

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class MyClass {
  public:
    int myNum;
    string myString;
    MyClass() {  // Constructor
      myNum = 0;
      myString = "";
    }
};

MyClass myObj;  // Create an object of MyClass

cout << myObj.myNum << endl;         // Output 0
cout << myObj.myString << endl;      // Output ""

Destructors

CPP

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class MyClass {
  public:
    int myNum;
    string myString;
    MyClass() {  // Constructor
      myNum = 0;
      myString = "";
    }
    ~MyClass() {  // Destructor
      cout << "Object destroyed." << endl;
    }
};

MyClass myObj;  // Create an object of MyClass

// Code here...

// Object is destroyed automatically when the program exits the scope

Class Methods

CPP

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class MyClass {
  public:
    int myNum;
    string myString;
    void myMethod() {  // Method/function defined inside the class
      cout << "Hello World!" << endl;
    }
};

MyClass myObj;  // Create an object of MyClass
myObj.myMethod();  // Call the method

Access Modifiers

CPP

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class MyClass {
  public:     // Public access specifier
    int x;    // Public attribute
  private:    // Private access specifier
    int y;    // Private attribute
  protected:  // Protected access specifier
    int z;    // Protected attribute
};

MyClass myObj;
myObj.x = 25;  // Allowed (public)
myObj.y = 50;  // Not allowed (private)
myObj.z = 75;  // Not allowed (protected)

Getters and Setters

CPP

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class MyClass {
  private:
    int myNum;
  public:
    void setMyNum(int num) {  // Setter
      myNum = num;
    }
    int getMyNum() {  // Getter
      return myNum;
    }
};

MyClass myObj;
myObj.setMyNum(15);  // Set the value of myNum to 15
cout << myObj.getMyNum() << endl;  // Output 15

Inheritance

CPP

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class Vehicle {
  public:
    string brand = "Ford";
    void honk() {
      cout << "Tuut, tuut!" << endl;
    }
};

class Car : public Vehicle {
  public:
    string model = "Mustang";
};

Car myCar;
myCar.honk();  // Output "Tuut, tuut!"
cout << myCar.brand + " " + myCar.model << endl;  // Output "Ford Mustang"

C++ Preprocessor

Preprocessor

{.marker-none .cols-2}

Includes

CPP

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#include "iostream"
#include <iostream>

Defines

CPP

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#define FOO
#define FOO "hello"

#undef FOO

CPP

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

Error

CPP

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

Macro

CPP

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

Token concat

CPP

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

Stringification

CPP

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

file and line

CPP

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

Miscellaneous

Escape Sequences

Escape Sequences	Characters
`\b`	Backspace
`\f`	Form feed
`\n`	Newline
`\r`	Return
`\t`	Horizontal tab
`\v`	Vertical tab
`\\`	Backslash
`\'`	Single quotation mark
`\"`	Double quotation mark
`\?`	Question mark
`\0`	Null Character

Keywords

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 {.marker-none .cols-5}

Preprocessor

Also see

C++ Infographics & Cheat Sheets (hackingcpp.com)
C++ reference (cppreference.com)
C++ Language Tutorials (cplusplus.com)

C++

Getting Started

C++ Arrays

C++ Conditionals

Relational Operators

Assignment Operators

Logical Operators

Bitwise Operators

C++ Loops

C++ Functions

C++ Classes & Objects

C++ Preprocessor

Miscellaneous

Also see

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