Lecture 4:Modern C++ Types

Modern C++ Types¶

Auto¶

If you use auto, the compiler will figure out the type of the variable by itself

auto is a compile-time thing.

Sometimes you don't know the type, and you need to ask the compiler to figure it out for you. It creates a class instance for you.

auto can be used in return type of function.(BUT IT IS NOT RECOMMENDED) But it cannot be used in function parameter.

Some guidelines for using auto:

Example:

auto calculateSum(const std::vector<int>& v) {
    auto copy = v; // copy is std::vector<int>
    auto multiplier = 2.4;
    auto name = "Avery";
    auto betterName = std::string("Avery");
    auto func = [](auto i) {return i * 2; }; // func is a lambda that takes one parameter of any type and returns the parameter multiplied by 2
    return std::accumulate(copy.begin(), copy.end(), 0) * multiplier;
}

Pair¶

C++17 allows structured binding, which makes it easier to unpack pairs and tuples.

std::pair is a simple container to store two heterogeneous objects as a single unit.(C++17)

#include <iostream>
#include <utility>

using namespace std;

pair<int, int> findPriceRange(int dist) {
    int min = static_cast<int>(dist * 0.08 + 100);
    int max = static_cast<int>(dist * 0.36 + 200);

    return make_pair(min, max);
}

int main() {
    int dist = 500;
    auto [minPrice, maxPrice] = findPriceRange(dist); // C++17 structured binding
    cout << "Min Price: " << minPrice << ", Max Price: " << maxPrice << endl;

    return 0;
}

Here, auto is used to automatically deduce the types of each variable.

Struct¶

Return multiple things from a function.

A struct is a collection of named variables grouped together.

struct Point {
    int x;
    int y;
};

Point createPoint(int x, int y) {
    return {x, y};
}

struct Point {
    int x;
    int y;
};

Point createPoint(int x, int y) {
    return {x, y};
}

Initialization¶

There are 27 ways to initialize a variable in C++.

C++11 adds uniform initialization using curly braces {}. It can be used for all types of initialization.

int a{10};              // basic type
int b = {20};           // same as above (copy form)
vector<int> v{1, 2, 3}; // container
pair<int, string> p{1, "hello"}; // pair
MyClass obj{1, 2, 3};   // custom class construction

```cpp int main() { vector vec1{3}; vector vec2(3); }

1. 基础类型¶

int, long, short, char, bool, float, double, void, wchar_t, char16_t, char32_t

2. 流程控制¶

if, else, switch, case, default, for, while, do, break, continue, goto, return

3. 存储/生命周期¶

static, extern, register, mutable, thread_local, inline

4. 常量 / 编译期¶

const, constexpr, consteval, constinit

5. 类型相关¶

auto, decltype, typename, using, typedef, signed, unsigned, volatile

6. 内存管理¶

new, delete

7. 面向对象¶

class, struct, union, enum, public, private, protected, this, friend, virtual, explicit, operator, template

8. 继承 / 多态¶

override, final

9. 模板 / 泛型编程¶

template, typename, concept, requires

10. 异常处理¶

try, catch, throw, noexcept

11. 命名空间 / 作用域¶

namespace, using, inline (namespace), alignas, alignof

12. 并发 / 原子¶

atomic_cancel, atomic_commit, atomic_noexcept, co_await, co_return, co_yield
（协程相关关键字也是 C++20 引入的）

13. 其他杂项¶

true, false, nullptr, sizeof, static_assert, typeid, dynamic_cast, reinterpret_cast, const_cast

14. 预处理指令（不是关键字，但常用）¶

#include, #define, #undef, #ifdef, #ifndef, #if, #else, #elif, #endif, #pragma

15. C 语言关键字（C++ 也支持）¶

auto, break, case, char, const, continue, default, do, double, else, enum, extern, float, for, goto, if, int, long, register, return, short, signed, sizeof, static, struct, switch, typedef, union, unsigned, void, volatile, while