C++ 함수 매개변수 전달 방법이 프로그램 성능에 미치는 영향

void foo(int num) {
  num++;  // 值传递副本，不会影响原始变量
}

int main() {
  int x = 5;
  foo(x);
  cout << x << endl; // 输出5，没有改变
}

void foo(int& num) {
  num++;  // 引用传递引用，更改原始变量
}

int main() {
  int x = 5;
  foo(x);
  cout << x << endl; // 输出6，已改变
}

#include <chrono>
#include <vector>

int sum_array_by_value(const std::vector<int>& arr) {
  int sum = 0;
  for (int i : arr) {
    sum += i;
  }
  return sum;
}

int sum_array_by_reference(std::vector<int>& arr) {
  int sum = 0;
  for (int& i : arr) {
    sum += i;
  }
  return sum;
}

int main() {
  std::vector<int> arr(1000000);
  for (int i = 0; i < arr.size(); i++) arr[i] = i;

  auto start = std::chrono::high_resolution_clock::now();
  int sum1 = sum_array_by_value(arr);
  auto end = std::chrono::high_resolution_clock::now();
  int elapsed1 = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();

  start = std::chrono::high_resolution_clock::now();
  int sum2 = sum_array_by_reference(arr);
  end = std::chrono::high_resolution_clock::now();
  int elapsed2 = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();

  std::cout << "Sum by value: " << elapsed1 << " ms" << std::endl;
  std::cout << "Sum by reference: " << elapsed2 << " ms" << std::endl;

  return 0;
}