header files

This is a discussion on header files within the C++ Programming forums, part of the General Programming Boards category; I've got a question : Is it good to use : Code: #indef SOMETHING_H #deinfe SOMEHING_H ... put your class ...

  1. #1
    the Great ElastoManiac's Avatar
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    Question header files

    I've got a question : Is it good to use :
    Code:
    #indef SOMETHING_H
    #deinfe SOMEHING_H
    ... put your class here ...
    #endif
    Since if you include the header two times you don't get an error. But it seems that with this kind of protection you can include header only once, and every time you try to do it again the compiler ignores it, which prevents tracking bugs.

    Isn't it better to include the headers properly without using that above, and if you make a mistake the compiler warns you and you correct it.

    So do you use that above. To me it seems stupid ? Can you explain me why i'm wrong ?
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  2. #2
    and the hat of wrongness Salem's Avatar
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    You can avoid it, but you have to be VERY careful about the order in which you include files.

    Also, if foo.h depends on bar.h, then you have to manually include bar.h BEFORE foo.h in all the places foo.h is included.

    In a large project, this kind of restriction can result in pages of #include at the beginning of each file and a maintenance nightmare.
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    >> Isn't it better to include the headers properly without using that above.
    Using header include guards is proper, IMO. Imagine if <string> did not have include guards. If you use a string object as a data member in multiple classes, and then use both those classes in a source file, what do you include? I can't think of a "proper" way to do that without the string header using include guards.

    >> every time you try to do it again the compiler ignores it, which prevents tracking bugs.
    I don't see how a header include guard prevents tracking bugs in any way. It only prevents a header from being included twice in the same compilation unit. While duplicate includes can be unnecessary, they don't cause much of a problem in general.

    There's really no reason to avoid header guards.

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    MFC killed my cat! manutd's Avatar
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    Quote Originally Posted by ElastoManiac
    Code:
    #deinfe
    Yeah, it would work if it was spelled right
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    Frequently Quite Prolix dwks's Avatar
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    Not to mention ifdef and the same macro name . . .

    and every time you try to do it again the compiler ignores it,
    . . . true . . .
    which prevents tracking bugs.
    false -- it's already been included into the file. If it would generate an error, the first instance would generate an error too.
    dwk

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  6. #6
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    Quote Originally Posted by ElastoManiac
    Since if you include the header two times you don't get an error. But it seems that with this kind of protection you can include header only once, and every time you try to do it again the compiler ignores it, which prevents tracking bugs.
    What kind of bug would it hide or prevent you from tracking?
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    (?<!re)tired Mario F.'s Avatar
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    ElastoManiac, check google for "C++ ODR headers guards". ODR stands for One Definition Rule.
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