How to know if the next character is EOF in C++

c++ eof
Tae picture Tae · Jun 8, 2011 · Viewed 59.5k times · Source

I'm need to know if the next char in ifstream is the end of file. I'm trying to do this with .peek():

if (file.peek() == -1)

and 

if (file.peek() == file.eof())

But neither works. There's a way to do this?

Edit: What I'm trying to do is to add a letter to the end of each word in a file. In order to do so I ask if the next char is a punctuation mark, but in this way the last word is left without an extra letter. I'm working just with char, not string.

Answer

zwol picture zwol · Jun 8, 2011

istream::peek() returns the constant EOF (which is not guaranteed to be equal to -1) when it detects end-of-file or error. To check robustly for end-of-file, do this:

int c = file.peek();
if (c == EOF) {
  if (file.eof())
    // end of file
  else
    // error
} else {
  // do something with 'c'
}

You should know that the underlying OS primitive, read(2), only signals EOF when you try to read past the end of the file. Therefore, file.eof() will not be true when you have merely read up to the last character in the file. In other words, file.eof() being false does not mean the next read operation will succeed.

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