我刚刚在this答案中找到一条评论,说在循环条件下使用iostream::eof
“几乎肯定是错误的”。我通常使用类似while(cin>>n)
的东西-我猜它隐式检查EOF。
为什么显式使用while (!cin.eof())
检查eof是错误的?
与在C语言中使用scanf("...",...)!=EOF
有什么不同(我经常会毫无问题地使用它)?
最佳答案
因为iostream::eof
仅在读取流的末尾后才返回true
。它并不表示下次读取将是流的结尾。
考虑一下(假设下一个读取将在流的末尾):
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:
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)
}
关于第二个问题:
if(scanf("...",...)!=EOF)
是相同的
if(!(inStream >> data).eof())
和不是与
if(!inStream.eof())
inFile >> data
关于c++ - 为什么在循环条件(即 `while (!stream.eof())`)内的iostream::eof被认为是错误的?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/63380335/