如何读取未知数量的输入？ [英] How to read unknown number of inputs?

问题描述

我正在使用C ++ Primer一书学习C ++。

在第1.4.3节中，以下示例代码用于读取未知数

  #include< iostream>。 
 int main（）
 {
 int sum = 0，值= 0; 
 //读取到文件结束，计算所有值的运行总和后读取
，而（std :: cin>>值）
 sum + = value; //等于sum = sum + value 
 std :: cout<< 总和为：<<总和<< std :: endl; 
返回0； 
} 
  

根据这本书，如果我们输入 3 4 5 6 ，输出将为总和为：18

但是当我在计算机上（带有MinGW的Windows 10 ）尝试此操作时，代码不会结束。即使我输入换行符，它也会继续要求输入。仅当我输入 f 之类的非整数输入时，它才起作用。

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这是预期的吗？如果是，输入换行符后是否有任何停止的代码？

我对c ++还是很陌生，我已经学习过python，所以遇到了麻烦

---

感谢和问候。

解决方案

您需要使用文件结尾字符（即Windows上的 CTRL-Z ， CTRL-D （在Mac / Unix上为>），而不仅仅是通过换行符（例如 Enter ）。

简单的 Enter 解释为空格，当读入整数数据类型时， operator>> 将被忽略。

$ b相反，$ b

CTRL-Z /文件结束会使任何 operator>> 失败，并显示错误。 / p>

另请参见此SO答案。

注意：输入 f 也会终止循环，因为不考虑 f 有效的整数；因此， std :: cin>>值，其中值的类型为 int ，输入内容为 f 也将失败。更准确地说： operator>> 实际上返回对输入流的引用，但是如果读取值失败，则 failbit 在流上设置，然后用布尔表达式（隐式调用 basic_istream :: operator bool（））解释流对象返回错误;所以也许这本书的作者不想在书的相应部分解释这些细节：-）

I am learning C++ using the book C++ Primer.

In Section 1.4.3, the following example code about reading the unknown number of inputs is given.

#include <iostream>
int main()
{
  int sum = 0, value = 0;
  // read until end-of-file, calculating a running total of all values read
  while (std::cin >> value)
  sum += value; // equivalent to sum = sum + value
  std::cout << "Sum is: " << sum << std::endl;
  return 0;
}

According to the book, if we give an input of 3 4 5 6, the output will be Sum is: 18

But when I try this on my computer(Windows 10 with MinGW), The code does not end. It just keeps on asking for input even if I enter a newline. It works only when I enter a non-int input like f.

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Is this expected? If yes, is there any code that stops after inputting a newline?

I am quite new to c++ and I have already learned python, so getting stuck so early on is quite frustrating.

---

Thanks and regards.

解决方案

You need to terminate your input by an End-Of-File-character (i.e. CTRL-Z on Windows, CTRL-D on Mac/Unix), not just by an End-Of-Line (i.e. Enter).

A simple Enter is interpreted as white space, which will be simply ignored by operator>> when reading into an integral data type.

CTRL-Z / End-Of-File, in contrast, makes any operator>> fail with an error.

See also this SO answer.

Note: Entering f will also terminate your loop, since f is not considered a valid integral number; Hence, std::cin >> value with value being of type int and an input like f will fail as well. To be more accurate: operator>> actually returns a reference to the input stream, but if reading in a value fails, failbit is set on the stream, and then interpreting the stream object in a boolean expression (implicitly calling basic_istream::operator bool()) returns false; So maybe the author of the book did not want to explain these details at the respective section in the book :-)

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