using new

This is a discussion on using new within the C++ Programming forums, part of the General Programming Boards category; How can a C++ developer use the placement new syntax to make new allocate an object of class SomeClass at ...

  1. #1
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    using new

    How can a C++ developer use the placement new syntax to make new allocate an object of class SomeClass at a particular memory address stored in a pointer type variable named pmem?

    A. new SomeClass(pmem);
    B. new(pmem) SomeClass;
    C. new SomeClass pmem;
    D. new pmem SomeClass;
    E. new (pmem, SomeClass);

    Hmm. This confuses me a bit as I'm only use to seeing:
    Code:
    someClass *pmem = new someClass;
    But I'm rather sure A is correct as its a copy constructor. And the rest are incorrect.

    Can anyone confirm. Thx.

  2. #2
    Cat without Hat CornedBee's Avatar
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    B is correct and the others are not. You are apparently unfamiliar with placement new.
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    C++ Witch laserlight's Avatar
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    Where did you get this question from? The word "allocate" is rather dangerous in this context since placement new is not used to allocate memory. Does your book mention anything on placement new? If not, you might want to search the web on "placement new".
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  4. #4
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    Quote Originally Posted by CornedBee
    You are apparently unfamiliar with placement new.
    I'm use to using malloc instead.

    Quote Originally Posted by laserlight
    Where did you get this question from?
    http://ikmnet.com/

    Quote Originally Posted by laserlight
    Does your book mention anything on placement new?
    Nope - was not aware of "placement new" until now.
    Last edited by coletek; 01-11-2009 at 11:29 AM.

  5. #5
    Cat without Hat CornedBee's Avatar
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    malloc and placement new have absolutely nothing to do with each other. In fact, they're pretty much orthogonal: malloc allocates memory, placement new constructs an object inside.
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    Quote Originally Posted by CornedBee
    malloc and placement new have absolutely nothing to do with each other. In fact, they're pretty much orthogonal: malloc allocates memory, placement new constructs an object inside.
    Just found that out now. Thx peoplez.

  7. #7
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    Quote Originally Posted by coletek View Post
    http://ikmnet.com/

    Nope - was not aware of "placement new" until now.
    So does that mean we're answering questions to help you get hired for a job you're not qualified for?
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    Kiss the monkey. CodeMonkey's Avatar
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    Written tests are given to determine job eligibility? How offensive. Aren't there degrees for that?
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  9. #9
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    Quote Originally Posted by CodeMonkey View Post
    Written tests are given to determine job eligibility? How offensive. Aren't there degrees for that?
    Degrees don't tell you much other than you spent a lot of money for a fancy piece of paper. The real question is, did you learn anything when you were taking all those courses, or did you just cheat your way through...
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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