exception from C function?

This is a discussion on exception from C function? within the C++ Programming forums, part of the General Programming Boards category; On a side note, Stroustrup is wrong about atexit(): since it only registers handlers and doesn't call them, it can't ...

  1. #16
    C++ Witch laserlight's Avatar
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    On a side note, Stroustrup is wrong about atexit(): since it only registers handlers and doesn't call them, it can't throw. The function that might throw is exit().
    Have you considered sending him an email to make the correction in an errata and/or future edition?
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  2. #17
    Cat without Hat CornedBee's Avatar
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    Hmm, perhaps I should. But I should check the errata first. Maybe it's already there.

    Edit: OK, the errata don't list anything. But I noticed that my 15th print is already behind the latest version, the 16th print.

    George, which print do you have? (It's on the very bottom of the legal info page.)
    Last edited by CornedBee; 01-28-2008 at 11:12 AM.
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  3. #18
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    Hi CornedBee,


    Quote Originally Posted by CornedBee View Post
    The actual rule is simple: catch all C++ exceptions at the end of a callback and use the callback's error reporting mechanism (typically a return code) to report the error. The callback doesn't have such a mechanism? (qsort's callback for example) Then there probably shouldn't be any errors. (How hard can comparing two objects be?)
    How could you do this if we are not allowed to modify the code of the callback function -- supposing it is from some 3rd party code? :-)

    I think the issue mentioned by Bjarne is common nowadays, and you know (1) invoking qsort is common and (2) compare function is common to throw exception, and from your analysis, undefined behavior is so often. :-)


    regards,
    George

  4. #19
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    I agree CornedBee -- aftre reading MSDN document about atexit()!


    I suggest you send him an email to let him correct his in next version. :-)

    Quote Originally Posted by CornedBee View Post
    On a side note, Stroustrup is wrong about atexit(): since it only registers handlers and doesn't call them, it can't throw. The function that might throw is exit().

    regards,
    George

  5. #20
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    Hi CornedBee,


    What do you mean print? The "Show Printable Version" at the bottom of the page?

    Quote Originally Posted by CornedBee View Post
    Hmm, perhaps I should. But I should check the errata first. Maybe it's already there.

    Edit: OK, the errata don't list anything. But I noticed that my 15th print is already behind the latest version, the 16th print.

    George, which print do you have? (It's on the very bottom of the legal info page.)

    regards,
    George

  6. #21
    Cat without Hat CornedBee's Avatar
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    For heaven's sake, learn to multiquote!

    1) I'd write a wrapper for the 3rd party function that catches all exceptions.
    2) Invoking qsort in C++ code shouldn't be common. std::sort is way better.
    3) A compare function should not commonly throw exceptions.
    4) No! Presumably, since you're quoting the book a lot, you have it, right? The book is reprinted whenever the copies run out, so there's the first print, the second print, and so on. Each new print has some minor corrections incorporated. My copy is the 15th print, but the newest is the 16th. I just want to know if you have this newest print, because then your quote would indicate that the problem hasn't been fixed.
    All the buzzt!
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  7. #22
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    Thanks CornedBee,


    1.

    Quote Originally Posted by CornedBee View Post
    2) Invoking qsort in C++ code shouldn't be common. std::sort is way better.
    Why std::sort is faster than qsort?

    2.

    Quote Originally Posted by CornedBee View Post
    4) No! Presumably, since you're quoting the book a lot, you have it, right? The book is reprinted whenever the copies run out, so there's the first print, the second print, and so on. Each new print has some minor corrections incorporated. My copy is the 15th print, but the newest is the 16th. I just want to know if you have this newest print, because then your quote would indicate that the problem hasn't been fixed.
    I am using The C++ Programming Language Special Edition 4th print -- pretty old. :-)


    regards,
    George

  8. #23
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    Yeah, but the issue is that atexit() is the means by which an exception can be made to occur when a program exits (by registering a function that throws).

  9. #24
    Cat without Hat CornedBee's Avatar
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    No, the issue is that the compiler can make assumptions about exceptions being thrown if it knows which calls might throw exceptions. And any C function that doesn't call a C++ callback cannot throw exceptions. This includes atexit(), because although a callback is passed to it, it doesn't call it.

    qsort is a C function, compiled into object code as it is. The callback is called through a function pointer.
    sort is a C++ function template, compiled into object code whenever instantiated. The callback can be a function object, allowing inlining of the comparison, thus greatly speeding up the execution.
    All the buzzt!
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  10. #25
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    Thanks CornedBee,


    1. What means "compiled into object code whenever instantiated"?

    2. Why (1) is faster than function callback implemented by function pointer?

    Quote Originally Posted by CornedBee View Post
    qsort is a C function, compiled into object code as it is. The callback is called through a function pointer.
    sort is a C++ function template, compiled into object code whenever instantiated. The callback can be a function object, allowing inlining of the comparison, thus greatly speeding up the execution.

    regards,
    George

  11. #26
    C++まいる!Cをこわせ!
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    Quote Originally Posted by George2 View Post
    1. What means "compiled into object code whenever instantiated"?
    You don't know how templates works?
    Because of their template-specific nature that they can use any type, the compiler only generates code when a call to the template function is made. You could save size, for one thing.

    2. Why (1) is faster than function callback implemented by function pointer?
    Inline! Hello?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  12. #27
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    Thanks Elysia,


    I agree with your below points. But if I understand correctly, generating only the type needed is used to save footprint to that no need to generate all possible types...

    But how could it improve performance?

    Quote Originally Posted by Elysia View Post
    You don't know how templates works?
    Because of their template-specific nature that they can use any type, the compiler only generates code when a call to the template function is made. You could save size, for one thing.


    Inline! Hello?

    regards,
    George

  13. #28
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    Quote Originally Posted by George2 View Post
    But how could it improve performance?
    How about avoiding function calls + overhead?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  14. #29
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    Quote Originally Posted by George2 View Post
    Thanks Elysia,


    I agree with your below points. But if I understand correctly, generating only the type needed is used to save footprint to that no need to generate all possible types...

    But how could it improve performance?
    By inlining the compare operation - the templated sort function just uses the < operator, so if it's an integer compare, it will just do that. If it's an inlinable operator< in the class object, then the compiler can inline it.

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  15. #30
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    Thanks Elysia,

    1.

    You mean the performance of template function invocation is because there is additional stack operation push/pop parameters, for example?

    If true, I do not think it is a special point which template function brings to us, all function call has such so-called "performance degration". :-)

    Have I understood your correctly?

    2.

    qsort() is a inline function?

    Quote Originally Posted by Elysia View Post
    How about avoiding function calls + overhead?

    regards,
    George

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