Embrace Modern C++

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# 💻 Embrace Modern C++

@luk036 👨‍💻 · 2026 📅

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## 🎬 Introduction

-   Why smart engineers write bad code?

---

### 🚀 C++ Evolution

.mermaid[
<pre>
graph LR
    A["C++11"] --> B["C++14"]
    B --> C["C++17"]
    C --> D["C++20"]
    D --> E["C++23"]
    
    style A fill:#4caf50
    style B fill:#ff9800
    style C fill:#2196f3
    style D fill:#9c27b0
    style E fill:#f44336
</pre>
]

---

### 📚 Resources

-   Books 📖
  -   Learn C++ for Game Development, Apress
  -   C++ Today, O'Reilly
  -   C++ Standard Library Quick Reference, Apress
-   Web resources 🌐
  -   <http://isocpp.org>
  -   <http://cppreference.com>
-   Online compilers 🖥️
  -   <https://wandbox.org>
  -   <http://ideone.com>
-   Conference 🎤
  -   <http://cppcon.org>

---

### 🛠️ C++17 Compilers

-   Windows 🪟:
  -   Visual Studio 2017 (good for beginners)
-   Linux 🐧:
  -   g++ 7.0 or later (with `-std=c++1z`)
  -   clang++ 4.0 or later (with `-std=c++1z`)
-   Online compilers 🖥️:
  -   <https://wandbox.org>
  -   <http://ideone.com>
  -   <http://stacked-crooked.com>
  -   <http://gcc.godbolt.org>

---

### 🔧 Use Clang++ with CMake

```bash
export CC=clang
export CXX=clang++
export CXXFLAGS="-g -std=c++1z"
cmake ../yourProject
make
```

---

### 🔀 Alternatively

-   System wide change on Ubuntu:
  -   type `sudo update-alternatives --config c++`
  -   will print something like this:

```terminal
         Selection Path Priority Status
         ------------------------------------------------------------
         * 0 /usr/bin/g++ 20 auto mode
           1 /usr/bin/clang++ 10 manual mode
           2 /usr/bin/g++ 20 manual mode
```

-   Then just select clang++

---

### 👋 "Hello, World!"

-   The minimal C++ program:

```cpp
int main(){}
```

-   A program that writes Hello, World!:

```cpp
#include <iostream>
int main()
{
    std::cout << "Hello, World!\n";
}
```

---

### 🎯 Uniform initialization

**Uniform initialization** simplifies the initialization of various
objects (e.g., obviating some constructor calls in function return
values)

```cpp
int a = 1; // old
int n{ 4 }; // new
int m{ 4.5 }; // error!
string s{ "foo" };
vector<int> values{1,2,4,7};
map<string, string> capitals {
  { "UK", "London" }, { "China", "Beijing"}
};
```

---

### 🎯 Uniform initialization (cont'd)

```cpp
struct Person {
    string name; int age; Address address;
    Person(const string& name, int age)
      : name(name), age(age) { }
};
struct Exchange {
    int count; float rates[2];
};
int main() {
    Person p { "Dmitri", 123 };
    Exchange e{ 1, 2, 3 }; // e.rates[0] = 2
                           // e.rates[1] = 3
}
```

---

### 📋 initializer list

```cpp
struct Exchange {
    int count; float rates[2];
    Exchange(initializer_list<float> r) {
        if (r.size() < 2) return;
        auto i = r.begin();
        rate[0] = *i++;
        rate[1] = *i;
    }
};
int main() {
    Exchange e{ 1, 2, 3 }; // e.rates[0] = 1
                           // e.rates[1] = 2
}
```

---

Automatic type deduction 🔍
------------------------

```cpp
auto a = 0;
auto b = 123.f;
auto c = "hello";
auto d = {1, 2, 4};
auto meaning_of_life() { return 42; }

map<string,vector<double>> ticks;
map<string,vector<double>>::iterator it = ticks.begin(); // old
auto it = ticks.begin(); // new
cout << meaning_of_life() << endl;
```

### 📌 Remarks

-   Almost Always Auto (AAA), but be careful template expressions.
-   Compilers may know better than you.

---

Automatic type deduction (cont'd) 📖
---------------------------------

```cpp
template <typename T, typename U>
auto add(T t, U u) -> decltype(t+u)
{
    return t+u;
}

int main() {
    cout << add(3, 4.5) << endl;
    cout << add(string("hello,"), "world") << endl;
}
```

In future,

```cpp
auto add(auto t, auto u)
{
    return t+u;
}
```

---

Range-based for loop (feature already in Python) 🔁
------------------------------------------------

**Non-member begin()/end() functions** simplify writing algorithms that
can operate on different collections (e.g., array or `vector`) and a
**range-based for loop**, especially coupled with `auto`, makes
iterating collections a lot easier.

```cpp
vector<int> v = {0,1,2,3,4,5,6,7,8,9};

for (auto x : v) // for each x in v
    cout << x << '\n';
for (auto&& x : {10,21,32,43,54,65})
    cout << x << '\n';
for (auto& x : v)
    ++x;
```

---

Nullptr 🎯
-------

```cpp
 // count the number of occurrences of x in p[]
 // p is assumed to point to a zero-terminated array
 // of char (or to nothing)
 int count_x(char* p , char x)
 {
     if (p==nullptr) return 0;
     int count = 0;
     for (; *p!=0; ++p)
        if (*p==x) ++count;
     return count;
 }
```

---

Lambda Expression in C++11 ⚡
--------------------------

-   New:

```cpp
int a = 42;
count_if(v.begin(), v.end(),
         [&a](int x) -> bool { return x == a; });
```

-   Old:

```cpp
struct functor  {
    int &a;
    functor(int& _a) : a(_a) {}
    bool operator()(int x) const { return a == x; }
};
int a = 42;
count_if(v.begin(), v.end(), functor(a));
```

---

Structured bindings (feature already in Python) 📦
-----------------------------------------------

```cpp
tuple<T1,T2,T3> f(/*...*/) { /*...*/ return {a,b,c}; }
auto [x,y,z] = f();
auto [x, string y, z] = f();
auto [x, ignore, z] = f();
```

---

Concept Lite (not yet in C++17) 🧩
-------------------------------

```cpp
template <class T>
concept Equality_Comparable() {
  return requires (T a, T b) {
    {a == b}->bool;
  };
}

template <class T>
  requires Equality_Comparable<T>()
bool operator!=(const T& a, const T& b) {
  return !(a == b);
}
```

---

Concept - requires 🧩
------------------

-   Now:

```cpp
template<typename Z, class = typename
  std::enable_if<std::is_integral<Z>::value>::type>
inline constexpr Z gcd(const Z& a, const Z& b) noexcept
{ return b == Z(0) ? abs(a) : gcd(b, a%b); }
```

-   Future:

```cpp
template<typename Z>
  requires std::is_integral<Z>::value
inline constexpr Z gcd(const Z& a, const Z& b) noexcept
{ return b == Z(0) ? abs(a) : gcd(b, a%b); }
```

---

Contracts (not yet in C++17) 📜
----------------------------

```cpp
T& operator[](int i)
   [[pre(bad_range{}): 0 < i && i < size()]]
{
    return elem[i];
}
```

---

Modules (not yet in C++17) 🧱
--------------------------

```cpp
import std.vector; // like #include <vector>
import std.string; // like #include <string>
import std.iostream; // like #include <iostream>
import std.iterator; // like #include <iterator>

int main() {
    using namespace std;
    vector<string> v = {
        "Socrates","Plato","Descartes","Kant","Bacon"
    };
    copy(begin(v),end(v),ostream_iterator<string>(cout,"\n"));
}
```

---

Standard Library 📚
----------------

---

### ⚠️ sprintf() Considered Harmful

-   `sprintf()` often creates buffer overflows that are hard to debug.

-   Use `std::to_chars()` or `std::to_string()` instead as possible.

---

### ⚠️ rand() Considered Harmful

```cpp
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main()
{
  srand(time(NULL));
  for (int i = 0; i < 16; ++i) {
     printf("%d ", rand() % 100); // What's wrong with this?
  }
  printf("\n");
}
```

---

### 🎲 Use random Library Instead

```cpp
#include <iostream>
#include <random>

int main()
{
  std::mt19937 mt(1729);
  std::uniform_int_distribution<int> dist(0,99);
  for (int i = 0; i < 16; ++i) {
    std::cout << dist(mt) << " ";
  }
  std::cout << std::endl;
}
```

---

### Even Simplier 💡

```cpp
#include <iostream>
#include <experimental/random>

int main()
{
  using std::experimental::randint;

for (int i = 0; i < 16; ++i) {
    std::cout << randint(0, 99) << " ";
  }
  std::cout << std::endl;
}
```

---

### How to shuffle a vector C++98 🃏

```cpp
#include <time.h>
#include <algorithm>
#include <vector>
using namespace std;
// ...
srand(time(NULL));
vector <Card> deck;
// some code to add cards to the deck here
random_shuffle ( deck.begin(), deck.end() );
```

---

### How to shuffle a vector C++11 🃏

```cpp
#include <random>
#include <algorithm>
//...
std::random_device rd;
std::mt19937 g(rd());
std::vector <Card> deck;
// some code to add cards to the deck here
std::shuffle(deck.begin(), deck.end(), g);
```

---

### How to measure runtime in C++11 ⏱️

```cpp
#include <chrono>
using namespace std::chrono;
// ...
auto const start = system_clock::now();
// ... code to measure
auto const elapsed =
  duration_cast<milliseconds>(system_clock::now() - start);
std::cout << "total elasped time = " << elapsed.count()
          << "ms." << std::endl;
```

---

### The Pimpl Idiom in C++11 🔒

```cpp
// file widget.h
#include <memory>
class widget {
  public:
    widget();  ~widget();
  // public and protected members
  private:
    struct impl;
    std::unique_ptr<impl> pimpl;
  // ptr to a forward-declared class
};
```

---

### The Pimpl Idiom in C++11 (cont'd) 🔒

```cpp
// file widget.cpp
#include "widget.h"

struct widget::impl {
  // private members; fully hidden, can be
  // changed at will without recompiling clients
};

widget::widget()
  : pimpl{ make_unique<widget::impl>(/*...*/) } { }
widget::~widget() = default;
```

---

### The variant type (a type-safe replacememt of union) 🎭

```cpp
variant<int,string> v = {"asdf"};
string s = get<string>(v);
v = 42;
string s2 = get<string>(v);
  // doesn't hold a string: throw bad_variant_access
```

---

### Herb Sutter's Favorite C++ 10-Liner 🏆

```cpp
shared_ptr<widget> get_widget( int id ) {
  static map<int, weak_ptr<widget>> cache;
  static mutex m;
  lock_guard<mutex> hold(m);
  auto sp = cache[id].lock();
  if (!sp) cache[id] = sp = load_widget(id);
  return sp;
}
widget& instance() {
  static widget w;
  return w;
}
```

---

Algorithm Development Using STL 🧮
-------------------------------

---

### 📚 Example - Insertion sort

```cpp
#include <algorithm>

template<class FwdIt, class Compare = std::less<> >
void insertion_sort(FwdIt first, FwdIt last, Compare cmp = Compare{})
{
  for (auto it = first; it != last; ++it)
    std::rotate(std::upper_bound(first, it, *it, cmp),
                it, std::next(it));
}
```

---

### Main program 🖥️

```cpp
int main()
{
    std::vector<int> V = { 5, 3, 8, 1, 6, 9, 3, 4 };
    insertion_sort(V.begin(), V.end());
    for (auto e : V) std::cout << e << " ";
    std::cout << '\n';
}
```

-   Test program can be found in <http://ideone.com/zJL68g>.

---

### 📚 Example - Selection Sort

```cpp
template<class FwdIt, class Compare = std::less<>>
void selection_sort(FwdIt first, FwdIt last, Compare cmp = Compare{})
{
  for (auto it = first; it != last; ++it) {
    auto selection = std::min_element(it, last, cmp);
    std::iter_swap(selection, it);
    assert(std::is_sorted(first, std::next(it), cmp));
  }
}
```

---

### 📚 Example - Quick Sort

```cpp
template<class FwdIt, class Compare = std::less<>>
void quickSort(FwdIt first, FwdIt last, Compare cmp = Compare{})
{
    auto const N = std::distance(first, last);
    if (N <= 1) return;
    auto const pivot = std::next(first, N / 2);
    std::nth_element(first, pivot, last, cmp);
    quickSort(first, pivot, cmp);
    quickSort(pivot, last, cmp);
}
```

---

### 📚 Example - Knapsack Problem

A thief considers taking ${\color{green} b}$ pounds of loot. The loot is
in the form of $n$ items, each with weight ${\color{darkcyan} a_i}$ and
value ${\color{purple} p_i}$. Any amount of an item can be put in the
knapsack as long as the weight limit ${\color{green} b}$ is not
exceeded.

] .pull-right[

![img](http://www.eecs.wsu.edu/~cook/aa/lectures/figures/clipart/burglar.gif)

]

---

### Greedy approach 💰

Take as much of the item with the highest value per pound
$({\color{purple} p_i}/{\color{darkcyan} a_i})$ as you can. If you run
out of that item, take from the next highest
$({\color{purple} p_i}/{\color{darkcyan} a_i})$ item. Continue until
knapsack is full.

---

### 📚 Example - Greedy Knapsack Algorithm

```cpp
template <class InputIt, typename T, typename F1, typename F2>
InputIt greedy_knapsack(InputIt first, InputIt last,
                        const T& b, F1 p, F2 a)
{
  using Item = typename InputIt::value_type;
  T init(0);
  std::sort(first, last, [&](Item& i1, Item& i2) {
            return a(i1) * p(i2) < a(i2) * p(i1); });
  InputIt it = std::find_if(first, last, [&](Item& i) {
                            return (init += a(i)) > b; });
  return it;
}
```

---

### Main Program 🖥️

```cpp
struct my_item { int _a, _p; /* ... */ };

int main() {
    std::vector<my_item> v{ {4,2}, {10,3}, {20, 4}, {7,2} };
    auto it2 = greedy_knapsack(begin(v), end(v), 15,
        [](my_item& i)->int { return i._p; },
        [](my_item& i)->int { return i._a; } );
    for (auto it1 = begin(v); it1 != it2; ++it1)
        cout << '(' << it1->_a << ", " << it1->_p << ')';
}
```

-   Test program can be found in <http://ideone.com/9ZK6ol>.

---

Q&A 🎤
-----

] .pull-right[

![image](figs/questions-and-answers.svg)

]