Online Resources for Preprocessor Directives

This is a discussion on Online Resources for Preprocessor Directives within the C++ Programming forums, part of the General Programming Boards category; Does anyone know of a tutorial or a lesson on Preprocessor Directives? I looked at MSDN Visual C++ refrence material ...

  1. #1
    Imperator of Darkness Luciferek's Avatar
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    Online Resources for Preprocessor Directives

    Does anyone know of a tutorial or a lesson on Preprocessor Directives?
    I looked at MSDN Visual C++ refrence material but it is written in such a way that I barely understand it. I am looking for something that explains it in plain english!
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  2. #2
    Codebot
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    Here is one: http://www.cplusplus.com/doc/tutorial/preprocessor.html

    There really aren't many preprocessor directives. The ones you will most likely use are:

    Code:
    #define
    #include
    #ifdef
    #else
    #endif
    #if 
    #pragma
    Honestly, I never really used anything else but those.
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  3. #3
    and the hat of wrongness Salem's Avatar
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    How much explaining does #include, #define and #if take?
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  4. #4
    Cat without Hat CornedBee's Avatar
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    #define is quite complex - macro substitution has some strange rules.

    There's also #error, which is very simple.
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    Frequently Quite Prolix dwks's Avatar
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    I've never used #line myself, but I've used tools which have (i.e. bison).

    I've often used defined(), which isn't a preprocessor directive, but it is related. And what about #elif?

    (Side question: are you supposed to put double-quotes around the text after a #error directive?)
    dwk

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  6. #6
    Cat without Hat CornedBee's Avatar
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    (Side answer: no.)

    defined() is a preprocessor keyword.

    #if cond1
    #elif cond2
    #endif

    ==

    #if cond1
    #else
    #if cond2
    #endif
    #endif

    Some other preprocessors don't support #elif, by the way.
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  7. #7
    Frequently Quite Prolix dwks's Avatar
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    (Aside: thank you.)

    As far as I know, #elif is ANSI standard . . . are you referring to other types of preprocessors, or what?
    dwk

    Seek and ye shall find. quaere et invenies.

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  8. #8
    Cat without Hat CornedBee's Avatar
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    Old, old, old preprocessors. But they still exist in some unices.
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  9. #9
    Technical Lead QuantumPete's Avatar
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    I believe there is also #ifndef, #undef and the string-ify operation.

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  10. #10
    Cat without Hat CornedBee's Avatar
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    Stringify, yes, and token concatenation.
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  11. #11
    Jack of many languages Dino's Avatar
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    Don't forget the Preprocessor variables too, like __LINE__ and such, if you want to learn about the Preprocessor capabilities. I used __LINE__ just the other day writing a return code checker macro when writing a C program that uses a lot of the new "xxxx_s" safe functions.
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