Thread: #define

  1. #1
    Registered User
    Join Date
    Jul 2009
    Belfast, Northern Ireland


    So what's the difference between #define and a variable apart from #define has no type and can't be changed? Or is that it?

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    I think the question I would ask is what they have in common. I'm pretty sure the answer is "nothing".

  3. #3
    Webhead Spidey's Avatar
    Join Date
    Jul 2009
    True, They have almost nothing in common. #define is a pre-preprocessor directive which simply does textual substitution. Whereas variables have a value and an address. The list is endless really..
    Spidey out!

  4. #4
    Join Date
    Oct 2007
    Inside my computer
    A variable is a chunk of memory that you can read and write.
    A define is simply a text-replacement tool that replaces all instances of x with y.
    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.

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