bad_alloc

This is a discussion on bad_alloc within the C++ Programming forums, part of the General Programming Boards category; Hello everyone, I am wondering except when there is no memory on heap, are there any other situations when we ...

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    bad_alloc

    Hello everyone,


    I am wondering except when there is no memory on heap, are there any other situations when we will get bad_alloc exceptions? For example, invalid input of the size (e.g. very huge number or zero or negative number) will cause exception?


    thanks in advance,
    George

  2. #2
    and the hat of wrongness Salem's Avatar
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    I think there is ample documentation on the web to tell you the answer to that.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    I only find out of memory as one situation, but I am not sure about others. MSDN also does not provide formal description when there will be bad_alloc exception.

    Quote Originally Posted by Salem View Post
    I think there is ample documentation on the web to tell you the answer to that.

    regards,
    George

  4. #4
    and the hat of wrongness Salem's Avatar
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    > MSDN also does not provide formal description when there will be bad_alloc exception.
    You should really look up what the standard says, not what a specific vendor says.

    Final draft of C++98

    Or maybe a pukka electronic copy, http://www.ncits.org/cplusplus.htm
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    Cat without Hat CornedBee's Avatar
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    Zero is a valid input to the allocator function. Huge numbers are also valid, although it's likely that there's not enough memory available. Negative numbers are technically impossible, because the argument is an unsigned number.

    operator new's behaviour is defined as either returning valid memory or throwing a bad_alloc. There's no other possibility. It may not return null. It may not throw anything else. Therefore, any allocation failure of any kind must be reported as a bad_alloc or lead to immediate program abortion. (A corruption of the heap management data, for example, would probably lead to termination.)
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    Quote Originally Posted by CornedBee View Post
    operator new's behaviour is defined as either returning valid memory or throwing a bad_alloc. There's no other possibility. It may not return null.
    What? Since when?
    Although I've never used it, I've known about the nothrow version of new for a long time: http://www.informit.com/guides/conte...eqNum=170&rl=1

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    operator new's behaviour is defined as either returning valid memory or throwing a bad_alloc. There's no other possibility. It may not return null. It may not throw anything else.
    But then is the output of my compiler wrong if the following program prints "Other error"?
    Code:
    #include <iostream>
    #include <stdexcept>
    
    class A
    {
        public:
        A() { throw 1; }
    };
    
    int main()
    {
        try {
            A* a = new A;
        }
        catch (std::bad_alloc&) {
            std::cout << "Allocation error\n";
        }
        catch (int) {
            std::cout << "Other error\n";
        }
    }
    On one hand it is good to know that the problem was not allocating the memory but an exception was thrown from the constructor of the object. On the other hand it would mean that simply catching bad_alloc is not sufficient in all cases.
    I might be wrong.

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  8. #8
    Cat without Hat CornedBee's Avatar
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    anon: The exception was thrown by the constructor and came from the new operator, not operator new.

    cpjust: nothrow new is another story.
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    C++ Witch laserlight's Avatar
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    But then is the output of my compiler wrong if the following program prints "Other error"?
    I don't think so, since it is the constructor that threw the exception.
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    Hi cpjust,


    Is nothrow new supported in Visual Studio 2008?

    Quote Originally Posted by cpjust View Post
    What? Since when?
    Although I've never used it, I've known about the nothrow version of new for a long time: http://www.informit.com/guides/conte...eqNum=170&rl=1

    regards,
    George

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    Hi laserlight,


    Why do you think it is the constructor who throw bad_alloc exception? I think the root cause should be in the new operator function.

    Quote Originally Posted by laserlight View Post
    I don't think so, since it is the constructor that threw the exception.

    regards,
    George

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    C++ Witch laserlight's Avatar
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    Why do you think it is the constructor who throw bad_alloc exception?
    Read your own post again. You asked: 'is the output of my compiler wrong if the following program prints "Other error"?'.

    Clearly, you were not asking about bad_alloc, but about some other exception.
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    Hi laserlight,


    I do not quite understand your points.

    You mentioned bad_alloc is thrown from constructor, but I think it should be thrown from operator new at frist, then constructor re-throw it.

    Anything wrong?

    Quote Originally Posted by laserlight View Post
    Read your own post again. You asked: 'is the output of my compiler wrong if the following program prints "Other error"?'.

    Clearly, you were not asking about bad_alloc, but about some other exception.

    regards,
    George

  14. #14
    C++ Witch laserlight's Avatar
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    You mentioned bad_alloc is thrown from constructor, but I think it should be thrown from operator new at frist, then constructor re-throw it.

    Anything wrong?
    Yes. I never said bad_alloc was thrown from the constructor of A. I said that some exception other than bad_alloc was thrown from the constructor of A.
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    Thanks laserlight,


    You mean?

    Code:
    throw 1;
    Quote Originally Posted by laserlight View Post
    Yes. I never said bad_alloc was thrown from the constructor of A. I said that some exception other than bad_alloc was thrown from the constructor of A.

    regards,
    George

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