Thread: problems with passing ostream variable

  1. #1
    Registered User
    Join Date
    Jul 2004

    problems with passing ostream variable

     string str;
                    if (x.animalType()==2 || x.animalType()==3)
                            str = std::cerr;
                    x.print(str.c_str()) << endl;
    and hte function is...
    ostream& animals::print(ostream& stream = cout) const {

    what im trying to do is, read from a file, and if its a dog or a cat, then it'll print out to the error stream.
    and if its any other animal then it'll print out to standard output (cout)

    any help why this code wont work?

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    Didn't we just do this in another thread?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Registered User jlou's Avatar
    Join Date
    Jul 2003
    Your variable str is a string, but then you try to assign the cerr stream to it. That won't work. Normally, you might have a variable and assign cout or cerr to it as appropriate. In this case, that variable would have to be a reference to ostream, so it is a little more sloppy because you cannot assign to a reference, only initialize it with something. I would suggest something like this:
    if (x.animalType()==2 || x.animalType()==3)
        x.print(std::cerr) << endl;
        x.print(std::cout) << endl;
    or this:
    ostream& stream = (x.animalType()==2 || x.animalType()==3) ? std::cerr : std::cout;
    x.print(stream) << endl;

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