为什么循环条件内的 iostream::eof （即 `while (!stream.eof())`）被认为是错误的？

我刚刚发现一条评论this回答说使用iostream::eof在循环条件中“几乎肯定是错误的”。我通常使用类似的东西while(cin>>n)- 我猜它隐式检查 EOF。

为什么显式使用检查 eofwhile (!cin.eof())错误的？

与使用有何不同scanf("...",...)!=EOF在C中（我经常使用它没有问题）？

Because iostream::eof只会返回true after读取流的末尾。确实如此not指示下一次读取将是流的末尾。

考虑这一点（并假设下一次读取将在流的末尾）：

while(!inStream.eof()){
  int data;
  // yay, not end of stream yet, now read ...
  inStream >> data;
  // oh crap, now we read the end and *only* now the eof bit will be set (as well as the fail bit)
  // do stuff with (now uninitialized) data
}

反对这一点：

int data;
while(inStream >> data){
  // when we land here, we can be sure that the read was successful.
  // if it wasn't, the returned stream from operator>> would be converted to false
  // and the loop wouldn't even be entered
  // do stuff with correctly initialized data (hopefully)
}

关于你的第二个问题：因为

if(scanf("...",...)!=EOF)

是相同的

if(!(inStream >> data).eof())

and not与

if(!inStream.eof())
    inFile >> data