为什么整数溢出导致C + + iostreams错误？ [英] Why does integer overflow cause errors with C++ iostreams?

问题描述

好的，所以我有一些问题，C + + iostreams感觉很奇怪，但它可能是定义的行为，考虑到发生在MSVC ++和G ++。

Ok, so I have some problems with C++ iostreams that feels very odd, but it is probably defined behaviour, considering this happens with both MSVC++ and G++.

我有这个程序：

#include <iostream>
using namespace std;

int main()
{
   int a;
   cin >> a;
   cout << a << endl;
   cin >> a;
   cout << a << endl;

   return 0;
}

如果我故意通过给第一个cin一个大于一个int的最大限制，所有进一步调用 cin.operator>>（）会立即返回一些原因， a 设置为某个值。该值似乎未定义。

If I intentionally overflow by giving the first cin a value that is larger than the max limit of an int, all further calls to cin.operator>>() will immediately return for some reason, and a is set to some value. The value seems to be undefined.

为什么，这个行为记录在哪里？有没有办法弄清楚这样的溢出是否发生？

Why, and where is this behavior documented? Is there a way to figure out if such an overflow occured?

此外，这个类似的程序似乎工作，我打算。如果我溢出的值，它会给 a 一些值，继续，如果溢出从未发生。

Also, this similar program seems to work as I intend. If I overflow the value, it will give a some value, and continue on as if the overflow never happened.

#include <cstdio>
using namespace std;

int main()
{
   int a;
   scanf("%d", &a);
   printf("%d\n", a);
   scanf("%d", &a);
   printf("%d\n", a);
   scanf("%d", &a);
   printf("%d\n", a);

   return 0;
}

推荐答案

iostreams旨在检测错误并进入错误状态。

iostreams is designed to detect errors and enter an error state. You get the same result from integer overflow as from entering a non-numeric string.

输入 cin （或任何流）到 bool 或检查 cin.rdstate（）以确定是否发生错误。

Cast cin (or any stream) to bool or check cin.rdstate() to determine if an error has occurred.

调用 cin.clear（）和 cin.ignore（）出错了。

对于官方文档，标准不幸在iostreams的肠子里有点不可思议。参见§27.6.1.2.1,27.6.1.2.2和22.2.2.1.1 / 11（不开玩笑）：

As for the official documentation, the Standard unfortunately gets a bit inscrutable in the bowels of iostreams. See §27.6.1.2.1, 27.6.1.2.2, and 22.2.2.1.1/11 (no kidding):

在阶段2中累积的字符序列将导致scanf报告输入失败。 ios_base :: failbit已分配给错误。

— The sequence of chars accumulated in stage 2 would have caused scanf to report an input failure. ios_base::failbit is assigned to err.

scanf的文档是不可穿透的，我会相信，溢出应该是一个错误。

The documentation for scanf is just as impenetrable, and I'll take it on faith that overflow is supposed to be an error.

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