Question about fstream

This is a discussion on Question about fstream within the C++ Programming forums, part of the General Programming Boards category; I have a question about using ifstream. From text book, it tells me we can use like following (1) Code: ...

  1. #1
    Registered User
    Join Date
    Feb 2010
    Posts
    32

    Question about fstream

    I have a question about using ifstream.
    From text book, it tells me we can use like following
    (1)
    Code:
        ifstream infile;
        infile.open("abc.txt");
        if(!infile)
           cerr << "Error: uanable to open input file" << endl;
    (2)
    However, I just codes from some others using ifstreams*..
    and I modify (1) to
    Code:
        ifstream* infile;
        infile->open("abc.txt");
        if(!(*infile))
           cerr << "Error: uanable to open input file" << endl;
    Both pass compiling process, but somehow if abc.txt doesn't exist, then
    (1) shows the correct cerr message
    (2) shows "Segmenation fault"

    Actually I don't quite get the meaning of fstream
    Isn't (2) same as (1)?
    Can I think of ifstream like a file pointer? Then it reads EOF or other error which returns false value in if(infile).. And ifstream* is a pointer pointer to a file pointer?

  2. #2
    The larch
    Join Date
    May 2006
    Posts
    3,573
    In the second case you don't have an object. You only have an uninitialized pointer pointing to some random garbage.

    Can I think of ifstream like a file pointer?
    You could, but it is rather an object managing a file pointer. You must have a fstream object to call open in the first place.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  3. #3
    Registered User
    Join Date
    Feb 2010
    Posts
    32
    Thx for replay, anon.

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