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c++ifstreameofpeek

Return value of ifstream.peek() when it reaches the end of the file

I was looking at this article on Cplusplus.com, http://www.cplusplus.com/reference/iostream/istream/peek/

I'm still not sure what peek() returns if it reaches the end of the file.

In my code, a part of the program is supposed to run as long as this statement is true

(sourcefile.peek() != EOF)

where sourcefile is my ifstream.

However, it never stops looping, even though it has reached the end of the file.

Does EOF not mean "End of File"? Or was I using it wrong?

Solution

  • Consulting the Standard,

    Returns:traits::eof() ifgood()isfalse. Otherwise,returnsrdbuf()->sgetc().

    As for sgetc(),

    Returns: If the input sequence read position is not available, returns underflow().

    And underflow,

    If the pending sequence is null then the function returns traits::eof() to indicate failure.

    So yep, returns EOF on end of file.

    An easier way to tell is that it returns int_type. Since the values of int_type are just those of char_type plus EOF, it would probably return char_type if EOF weren't possible.

    As others mentioned, peek doesn't advance the file position. It's generally easiest and best to just loop on while ( input_stream ) and let failure to obtain additional input kill the parsing process.