C++11数组初始化

李东岳

记录一下，还没用过。

在11之前，只能

class Something
{
private:
    const int m_array[5];
 
public:
    Something(): m_array {} // zero the member array
    {
        // If we want the array to have values, we'll have to use assignment here
    }
 
};

在11之后，可以数组直接初始化：

class Something
{
private:
    const int m_array[5];
 
public:
    Something(): m_array { 1, 2, 3, 4, 5 } // use uniform initialization to initialize our member array
    {
    }
 
};

http://www.learncpp.com/cpp-tutorial/8-5a-constructor-member-initializer-lists/

random_ran

这样改进的好处是什么呢？

我的c++基础也都是从 learncpp 上学来的，那个博主真的是用心。

wwzhao

@random_ran 初始化列表，在构造的同时赋值，提高执行效率

random_ran

@wwzhao

简单的感受了一下两种赋值方式，效率确实很大提高。

#include <stdio.h>
#include <string>
#include <chrono>
#include <iostream>

using namespace std ;

class Timer
{
private:
  // Type aliases to make accessing nested type easier                                                                                                                                          
  using clock_t = std::chrono::high_resolution_clock;
  using second_t = std::chrono::duration<double, std::ratio<1> >;

  std::chrono::time_point<clock_t> m_beg;

public:
  Timer() : m_beg(clock_t::now())
  {
  }

  void reset()
  {
    m_beg = clock_t::now();
  }

  double elapsed() const
  {
    return std::chrono::duration_cast<second_t>(clock_t::now() - m_beg).count();
  }
};

class SomethingBefore11
{
private:
  int m_array[5];

public:
   SomethingBefore11() // zero the member array                                                                                                                                                  
  {
    // If we want the array to have values, we'll have to use assignment here                                                                                                                    
    m_array[0] = 1;
    m_array[1] = 2;
    m_array[2] = 3;
    m_array[3] = 4;
    m_array[4] = 5;
  }
};

class SomethingAfter11
{
private:
  int m_array[5];

public:
  SomethingAfter11(): m_array { 1, 2, 3, 4, 5 } //zero the member array                                                                                                                          
  {
  }

};
int main(){

  Timer tBefore11;
  SomethingBefore11 m_array_before11;
  std::cout << "Time elapsed: " << tBefore11.elapsed() << ‘n’;

  Timer tAfter11;
  SomethingAfter11 m_array_after11;
  std::cout << "Time elapsed: " << tAfter11.elapsed() << ‘n’;
  return 0;

}

[xx OFtutorial0_helloWorld]$ whatAboutThisGuy
Time elapsed: 7.506e-06
Time elapsed: 1.47e-07
[xx OFtutorial0_helloWorld]$ whatAboutThisGuy
Time elapsed: 8.664e-06
Time elapsed: 1.9e-07
[xx OFtutorial0_helloWorld]$ whatAboutThisGuy
Time elapsed: 7.646e-06
Time elapsed: 1.89e-07