C++开发EOS基础指南：迭代器和Lambda表达式_cpp 迭代器与lambda表达式

让我们来谈谈迭代器，它是一个非常有用的工具，在整个EOS代码库中大量使用。如果您来自JavaScript背景，您可能已经熟悉迭代器，就像它们用于循环一样。迭代器的关键概念是提供一种更好的方法来遍历项集合。额外的好处是您可以为任何自定义类实现迭代器接口，使迭代器成为遍历数据的通用方法。

// @url: https://repl.it/@MrToph/CPPBasics-Iterators
#include <iostream>
#include <vector>

using namespace std;

int main()
{
  vector<int> v{2, 3, 5, 8};
  // old way to iterate
  for (int i = 0; i < v.size(); i++)
  {
    cout << v[i] << "\n";
  }

  // using Iterators
  // begin() returns an iterator that points to the beginning of the vector
  // end() points to the end, can be compared using != operator
  // iterators are incremented by using the + operator thanks to operator-overloading
  for (vector<int>::iterator i = v.begin(); i != v.end(); i++)
  {
    // iterators are dereferenced by * like pointers
    // returns the element the iterator is currently pointing to
    cout << *i << "\n";
  }

  // auto keyword allows you to not write the type yourself
  // instead C++ infers it from the return type of v.begin
  for (auto i = v.begin(); i != v.end(); i++)
  {
    cout << *i << "\n";
  }

  // can use arithmetic to "jump" to certain elements
  int thirdElement = *(v.begin() + 2);
  cout << "Third: " << thirdElement << "\n";
  // end is the iterator that points to the "past-the-end" element
  // The past-the-end element is the theoretical element that would follow the last element in the vector.
  // It does not point to any element, and thus shall not be dereferenced.
  int lastElement = *(v.end() - 1);
  cout << "Last: " << lastElement << "\n";

  // do not go out of bounds by iterating past the end() iterator
  // the behavior is undefined
  // BAD: v.end() + 1, v.begin() + 10
}
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在现代C++中，迭代器是迭代元素集合（向量，列表，映射）的首选方式。另外，auto关键字可以避免输入word类型，但可能会导致代码性能降低。

Lambda表达式

使用迭代器，