无限循环，不接受输入

问题描述

我编写一个简单的C ++程序，它将动态内存分配给我的程序，然后删除这个内存。这是我的计划：

I am writing a simple C++ Program which allocates dynamic memory to my Program and then deletes this memory. Here is my Program:

#include <iostream>
#include <new>
using namespace std;

int main ()
{
  int i,n;
  int * p;
  cout << "How many numbers would you like to type? ";
  cin >> i;
  p= new (nothrow) int[i];
  if (p == nullptr)
    cout << "Error: memory could not be allocated";
  else
  {
    for (n=0; n<i; n++)
    {
      cout << "Enter number: ";
      cin >> p[n];
    }
    cout << "You have entered: ";
    for (n=0; n<i; n++)
      cout << p[n] << ", ";
    delete[] p;
  }
  return 0;
}

在上述程序中，当我输入i的值等于或小于20亿比这个计划工作正如预期。然而，当我输入高于20亿的任何东西，如30亿或更高，这个程序进入无限循环，没有在我的for循环中输入数字。

In the above program when I input the value of i (Number of inputs) equal to or less than 2 Billion than this program works as expected. However when I enter anything above 2 Billion like 3 Billion or higher, this program goes in an infinite loop without taking a number input in my for loop.

我期望这个程序失败，当我进入一个非常高的价值，因为它不能分配内存。

I am expecting this program to fail when I enter a very high value for i by saying it could not allocate the memory.

根据我的理解，我想当我进入一个非常高的价值的int i，我将走出整数数据类型，但仍然在这种情况下，它应该从for循环中我的数字输入，因为我有一个cin语句，而不是进入循环或内存分配应该简单地失败。

As per my understanding, I think when I enter a very high value of int i, I am going out of bound for integer data type but still in this case, it should take number input from me in for loop as I have a cin statement there instead of going in for loop or memory allocation should fail simply.

当我将i的类型从int更改为long时，它很有效，但我很想知道为int类型，为什么它进入无限循环，而不是取值当它看到cin in for循环？

When I changed type of i from int to long then it works but I am curious to know for i of type int, why it goes in infinite loop instead of taking values when it sees cin in for loop?

我在Mac OS X上运行这个程序，并使用g ++编译器编译它。

I am running this program on Mac OS X and compiling it using g++ compiler.

推荐答案

1）您尝试分配给 int 大于2147483647的值，这通常是此类型的最大值。
一般来说，如果你想处理这么大的数字，你应该使用 long long int （或者从< cstdint> 以便更好的可移植性）。

1) You are trying assign to int value bigger than 2147483647, which is usually maximum value for this type.Generally, if you want to handle such a large numbers, you should use long long int (or something from <cstdint> for better portability).

2）您不清除 cin 它失败。
代码bollow生成无限循环：

2) You don't clear state of cin after it fails.The code bollow generate infinite loop:

int i = 0;
while (i <= 0)
{
    std::cout << "Enter a number greater than 10..." << std::endl;
    std::cin >> i;
}

您可以这样解决：

int i = 0;
while (i <= 0)
{
    std::cout << "Enter a number greater than 10..." << std::endl;
    if (!(std::cin >> i))
    {
        std::cin.clear();  // Clear error flag
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');  // Remove incorrect data from buffer
    }
}

试图创建一个真正的大数组。你需要几个GiB的
连续内存。即使你成功分配数组，它仍然是一个设计问题。您应该使用许多较小的数组或使用/创建一个合适的容器。

3) You are trying to create a really big array. You need a few GiB ofcontiguous memory to this. Even if you succeed allocate the array, it is still a design issue. You should use many of smaller arrays or use/create a suitable container.

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