提供基本语法和方法的 C++ 快速参考备忘单
#include <iostream>
int main() {
std::cout << "Hello Quick Reference\n";
return 0;
}编译运行
$ g++ hello.cpp -o hello
$ ./hello
Hello Quick Referenceint number = 5; // 整数
float f = 0.95; // 浮点数
double PI = 3.14159; // 浮点数
char yes = 'Y'; // 特点
std::string s = "ME"; // 字符串（文本）
bool isRight = true; // 布尔值
// 常量
const float RATE = 0.8;int age {25}; // 自 C++11
std::cout << age; // 打印 25| 数据类型 | 大小 | 范围 |
|---|---|---|
int |
4 bytes | -231 到 231-1 |
float |
4 bytes | N/A |
double |
8 bytes | N/A |
char |
1 byte | -128 到 127 |
bool |
1 byte | true / false |
void |
N/A | N/A |
wchar_t |
2 到 4 bytes | 1 个宽字符 |
int num;
std::cout << "Type a number: ";
std::cin >> num;
std::cout << "You entered " << num;int a = 5, b = 10;
std::swap(a, b);
// 输出: a=10, b=5
std::cout << "a=" << a << ", b=" << b;// C++中的单行注释
/* 这是一个多行注释
在 C++ 中 */if (a == 10) {
// do something
}查看: 条件
for (int i = 0; i < 10; i++) {
std::cout << i << "\n";
}查看: 循环 Loops
#include <iostream>
void hello(); // 声明
int main() { // 主函数
hello(); // 执行函数
}
void hello() { // 定义
std::cout << "Hello Quick Reference!\n";
}查看: 函数 Functions
int i = 1;
int& ri = i; // ri 是对 i 的引用
ri = 2; // i 现在改为 2
std::cout << "i=" << i;
i = 3; // i 现在改为 3
std::cout << "ri=" << ri;ri 和 i 指的是相同的内存位置
#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();
}名称空间允许名称下的全局标识符
std::array<int, 3> marks; // 定义
marks[0] = 92;
marks[1] = 97;
marks[2] = 98;
// 定义和初始化
std::array<int, 3> = {92, 97, 98};
// 有空成员
std::array<int, 3> marks = {92, 97};
std::cout << marks[2]; // 输出: 0┌─────┬─────┬─────┬─────┬─────┬─────┐
| 92 | 97 | 98 | 99 | 98 | 94 |
└─────┴─────┴─────┴─────┴─────┴─────┘
0 1 2 3 4 5std::array<int, 6> marks = {
92, 97, 98, 99, 98, 94
};
// 打印第一个元素
std::cout << marks[0];
// 将第 2 个元素更改为 99
marks[1] = 99;
// 从用户那里获取输入
std::cin >> marks[2];char ref[5] = {'R', 'e', 'f'};
// 基于范围的for循环
for (const int &n : ref) {
std::cout << std::string(1, n);
}
// 传统的for循环
for (int i = 0; i < sizeof(ref); ++i) {
std::cout << ref[i];
} 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] << " ";
}
}
// 输出: 1 2 3 4 5 6 6 5 4 3 2 1 if (a == 10) {
// do something
}int number = 16;
if (number % 2 == 0)
{
std::cout << "even";
}
else
{
std::cout << "odd";
}
// 输出: evenint 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?";| :-- | -- |
|---|---|
a == b |
a 等于 b |
a != b |
a 不等于 b |
a < b |
a 小于 b |
a > b |
a 大于 b |
a <= b |
a 小于或等于 b |
a >= b |
a 大于或等于 b |
| 范例 | 相当于 |
|---|---|
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 |
| Example | Meaning |
|---|---|
exp1 && exp2 |
Both are true (AND) |
| `exp1 | |
!exp |
exp is false (NOT) |
| Operator | Description |
|---|---|
a & b |
Binary AND |
| `a | b` |
a ^ b |
Binary XOR |
a ~ b |
Binary One's Complement |
a << b |
Binary Shift Left |
a >> b |
Binary Shift Right |
┌── True ──┐
Result = Condition ? Exp1 : Exp2;
└───── False ─────┘
int x = 3, y = 5, max;
max = (x > y) ? x : y;
// 输出: 5
std::cout << max << std::endl;int x = 3, y = 5, max;
if (x > y) {
max = x;
} else {
max = y;
}
// 输出: 5
std::cout << max << std::endl;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;
}int i = 0;
while (i < 6) {
std::cout << i++;
}
// 输出: 012345int i = 1;
do {
std::cout << i++;
} while (i <= 5);
// 输出: 12345for (int i = 0; i < 10; i++) {
if (i % 2 == 0) {
continue;
}
std::cout << i;
} // 输出: 13579while (true) { // true or 1
std::cout << "无限循环";
}for (;;) {
std::cout << "无限循环";
}for(int i = 1; i > 0; i++) {
std::cout << "infinite loop";
}#include <iostream>
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;
}for (int n : {1, 2, 3, 4, 5}) {
std::cout << n << " ";
}
// 输出: 1 2 3 4 5std::string hello = "Quick Reference.ME";
for (char c: hello)
{
std::cout << c << " ";
}
// 输出: Q u i c k R e f . M E int password, times = 0;
while (password != 1234) {
if (times++ >= 3) {
std::cout << "Locked!\n";
break;
}
std::cout << "Password: ";
std::cin >> password; // input
}for (int i = 0, j = 2; i < 3; i++, j--){
std::cout << "i=" << i << ",";
std::cout << "j=" << j << ";";
}
// 输出: i=0,j=2;i=1,j=1;i=2,j=0;#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
void fun(string a, string b) {
std::cout << a + " " + b;
}
void fun(string a) {
std::cout << a;
}
void fun(int a) {
std::cout << a;
}#include <iostream>
#include <cmath> // 导入库
int main() {
// sqrt() 来自 cmath
std::cout << sqrt(9);
}- if
- elif
- else
- endif
- ifdef
- ifndef
- define
- undef
- include
- line
- error
- pragma
- defined
- __has_include
- __has_cpp_attribute
- export
- import
- module
#include "iostream"
#include <iostream>#define FOO
#define FOO "hello"
#undef FOO#ifdef DEBUG
console.log('hi');
#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
DST(object); #=> object_s object_t;#define STR(name) #name
char * a = STR(object); #=> char * a = "object";#define LOG(msg) console.log(__FILE__, __LINE__, msg)
#=> console.log("file.txt", 3, "hey")| 转义序列 | 说明 |
|---|---|
\b |
退格键 |
\f |
换页 |
\n |
换行 |
\r |
返回 |
\t |
水平制表符 |
\v |
垂直制表符 |
\\ |
反斜杠 |
\' |
单引号 |
\" |
双引号 |
\? |
问号 |
\0 |
空字符 |
- 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
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- 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
- if
- elif
- else
- endif
- ifdef
- ifndef
- define
- undef
- include
- line
- error
- pragma
- defined
- __has_include
- __has_cpp_attribute
- export
- import
- module
- C++ Infographics & Cheat Sheets (hackingcpp.com)
- C++ reference (cppreference.com)
- C++ Language Tutorials (cplusplus.com)