为什么在C ++中针对基于范围的for循环收到警告？ [英] Why am I getting a warning for this range-based for loop in C++?

问题描述

我目前正在使用Bjarne Stroustrup的书（第二版）自学C ++。在其中一个示例中，他使用范围循环来读取向量中的元素。当我为自己编写和编译代码时，会收到此警告。当我运行代码时，它似乎正在工作并计算平均值。为什么收到此警告，我应该忽略它吗？另外，为什么在示例中使用int而不是double的range-却返回double？

I am currently self-teaching myself C++ using Bjarne Stroustrup's book (2nd ed). In one of the examples, he uses a range-for-loop to read the elements in a vector. When I wrote and compiled the code for myself I get this warning. When I run the code, it seems to be working and calculates the mean. Why am I receiving this warning and should I ignore it? Also, why is the range-for using int instead of double in the example, but still returns a double?

temp_vector.cpp:17:13: warning: range-based for loop is a C++11 
extension [-Wc++11-extensions]

这是代码

#include<iostream>
#include<vector>

using namespace std;

int main ()
{
  vector<double> temps;     //initialize a vector of type double

  /*this for loop initializes a double type vairable and will read all 
    doubles until a non-numerical input is detected (cin>>temp)==false */
  for(double temp; cin >> temp;)
    temps.push_back(temp);

  //compute sum of all objects in vector temps
  double sum = 0;

 //range-for-loop: for all ints in vector temps. 
  for(int x : temps)     
    sum += x;

  //compute and print the mean of the elements in the vector
      cout << "Mean temperature: " << sum / temps.size() << endl;

  return 0;
}

类似地，我应该如何看待范围

On a similar note: how should I view the range-for in terms of a standard for loop?

推荐答案

通过-std = c ++ 11 编译器；您的（古老的）编译器默认使用C ++ 03，并警告您它正在​​接受某些较新的C ++结构作为扩展。

Pass --std=c++11 to the compiler; your (ancient) compiler is defaulting to C++03 and warning you that it is accepting some newer C++ constructs as extensions.

Range的范围已扩展放入基于迭代器的for循环中，但出现错别字的机会更少。

Ranged base for is expanded into an iterator-based for loop, but with less opportunities for typos.

这篇关于为什么在C ++中针对基于范围的for循环收到警告？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！