[C++] 複数の変数を効率的に初期化する方法

  #include <iostream>
  int main() {
      int number(10); // 直接初期化
      std::cout << number << std::endl;
      return 0;
  }

  10

  #include <iostream>
  int main() {
      int number = 10; // コピー初期化
      std::cout << number << std::endl;
      return 0;
  }

  10

#include <iostream>
int main() {
    int number{10}; // リスト初期化
    std::cout << number << std::endl;
    return 0;
}

10

#include <iostream>
class Example {
public:
    int number = 0; // デフォルト初期化
};
int main() {
    Example ex;
    std::cout << ex.number << std::endl;
    return 0;
}

0

#include <iostream>
struct Point {
    int x;
    int y;
};
int main() {
    Point p = {10, 20}; // 構造体を使った初期化
    std::cout << "x: " << p.x << ", y: " << p.y << std::endl;
    return 0;
}

x: 10, y: 20

#include <iostream>
int main() {
    int numbers[] = {1, 2, 3, 4, 5}; // 配列を使った初期化
    for (int i = 0; i < 5; ++i) {
        std::cout << "numbers[" << i << "]: " << numbers[i] << std::endl;
    }
    return 0;
}

numbers[0]: 1
numbers[1]: 2
numbers[2]: 3
numbers[3]: 4
numbers[4]: 5

#include <iostream>
#include <tuple>
int main() {
    std::tuple<int, double, std::string> data = std::make_tuple(1, 3.14, "Hello"); // std::tupleを使った初期化
    std::cout << "int: " << std::get<0>(data) << ", double: " << std::get<1>(data) << ", string: " << std::get<2>(data) << std::endl;
    return 0;
}

int: 1, double: 3.14, string: Hello

#include <iostream>
class Example {
public:
    int number;
    double value;
    // 初期化リストを使ったコンストラクタ
    Example(int n, double v) : number(n), value(v) {}
};
int main() {
    Example ex(10, 3.14);
    std::cout << "number: " << ex.number << ", value: " << ex.value << std::endl;
    return 0;
}

number: 10, value: 3.14

#include <iostream>
class Example {
public:
    int number;
    double value;
    // コンストラクタでの初期化
    Example() {
        number = 0;
        value = 0.0;
    }
};
int main() {
    Example ex;
    std::cout << "number: " << ex.number << ", value: " << ex.value << std::endl;
    return 0;
}

number: 0, value: 0

#include <iostream>
#include <memory>
int main() {
    // スマートポインタの初期化
    std::unique_ptr<int> ptr = std::make_unique<int>(10);
    std::cout << "Value: " << *ptr << std::endl;
    return 0;
}

Value: 10

#include <iostream>
#include <string>
class Person {
public:
    std::string name;
    int age;
    double height;
    // 初期化リストを使ったクラスメンバーの一括初期化
    Person(const std::string& n, int a, double h) : name(n), age(a), height(h) {}
};
int main() {
    Person person("Taro", 30, 175.5);
    std::cout << "Name: " << person.name << ", Age: " << person.age << ", Height: " << person.height << std::endl;
    return 0;
}

Name: Taro, Age: 30, Height: 175.5

#include <iostream>
#include <vector>
class Point {
public:
    int x, y;
    Point(int x, int y) : x(x), y(y) {}
};
int main() {
    std::vector<Point> points = { {1, 2}, {3, 4}, {5, 6} }; // 複数のオブジェクトの同時初期化
    for (const auto& point : points) {
        std::cout << "x: " << point.x << ", y: " << point.y << std::endl;
    }
    return 0;
}

x: 1, y: 2
x: 3, y: 4
x: 5, y: 6

#include <iostream>
#include <map>
#include <string>
int main() {
    // データ構造の初期化
    std::map<std::string, int> scores = { {"Alice", 90}, {"Bob", 85}, {"Charlie", 95} };
    for (const auto& [name, score] : scores) {
        std::cout << "Name: " << name << ", Score: " << score << std::endl;
    }
    return 0;
}

Name: Alice, Score: 90
Name: Bob, Score: 85
Name: Charlie, Score: 95