cin.clear() 不会重置 cin 对象

发布于 2024-12-04 12:01:57 字数 362 浏览 3 评论 0原文

我有以下循环。它应该读取数字，直到 EndOfFile，或者用户输入 -999

int arr[100];

int index;

for (index = 0; index < 100; index++)
{
 cin >> arr[index];
 if (!cin)
 {
  cin.clear();
  index--;
  continue;
 }
 if (arr[index] == -999)
 {
     break;
 }
}

当用户输入无效的内容（例如某些 char）时，此循环将永远重复，而不会 < code>清除错误状态或停止。

原文

I have the following loop. It should read numbers until EndOfFile, or the user input -999

int arr[100];

int index;

for (index = 0; index < 100; index++)
{
 cin >> arr[index];
 if (!cin)
 {
  cin.clear();
  index--;
  continue;
 }
 if (arr[index] == -999)
 {
     break;
 }
}

When the user input an invalid thing, such as some chars, this loop is being repeated for ever without clearing the error state or stopping.

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哑 2024-12-11 12:01:57

调用 clear 后，您还必须以某种方式从流中删除无效输入。这是一种方法：

 cin >> arr[index];
 if (!cin)
 {
  cin.clear();
  std::string ignoreLine; //read the invalid input into it
  std::getline(cin, ignoreLine); //read the line till next space
  index--;
  continue;
 }

这是因为当 cin 无法读取无效输入时，它会保留在流中。必须通过某种方式将其删除。我只是阅读并忽略它。

您还可以使用ignore作为：

cin.clear();
cin.ignore(std::numeric_limits<streamsize>::max(),' ');

在我看来，如果输入以空格分隔（并且如果您不想检查输入无效）。在线文档说：

istream::忽略
istream&忽略（流大小n = 1，int delim = EOF）；
提取并丢弃字符
从输入序列中提取字符并丢弃它们。
当提取完n个字符后，提取结束
丢弃或找到字符 delim 时，以先到者为准。
在后一种情况下，定界字符本身也会被提取。

After calling clear, you must also somehow remove the invalid input from the stream. Here is one way:

 cin >> arr[index];
 if (!cin)
 {
  cin.clear();
  std::string ignoreLine; //read the invalid input into it
  std::getline(cin, ignoreLine); //read the line till next space
  index--;
  continue;
 }

It's because when cin fails to read the invalid input, it remains there in the stream. It has to be removed, by some means. I just read and ignore it.

You can also use ignore as:

cin.clear();
cin.ignore(std::numeric_limits<streamsize>::max(),' ');

which is better in my opinion provided inputs are space separated (and if you don't want to inspect the invalid input). The online doc says:

istream::ignore
istream& ignore( streamsize n = 1, int delim = EOF );
Extract and discard characters
Extracts characters from the input sequence and discards them.
The extraction ends when n characters have been extracted and
discarded or when the character delim is found, whichever comes first.
In the latter case, the delim character itself is also extracted.

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