Difference between Staic and Const Keywords

This is a discussion on Difference between Staic and Const Keywords within the C Programming forums, part of the General Programming Boards category; i would like to know the difference between these two in detail. Thanks...

  1. #1
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    Difference between Staic and Const Keywords

    i would like to know the difference between these two in detail.
    Thanks

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Const just says this variable's value won't change, and so trying to change it will yield a compile error.
    Static can mean different things depending on where it's used. If used in a function, it will create a variable which retains its value between function calls. Its lifetime is from the beginning of the program to the end.
    On a global level, it has a different meaning, though. I'm sure someone else can fill in on that, but I'd just avoid it. It's not really necessary.
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    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

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  3. #3
    spurious conceit MK27's Avatar
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    A const is a value which does not change.
    Code:
    const int x = 5;
    You cannot change the value of x without casting it non-const.

    A static variable maintains it's value between function calls:
    Code:
    void test() {
         static int x = 5;
         x++;
         printf("%d\n",x);
    }
    The first time you call test(), x will be 6. Next time it will be 7, and so on. Ie, because it is static, it is initialized only once during execution (sort of like a global, for which they are useful replacements).

    A static function limits the declaration to file scope:
    Code:
    static void test();
    This will not be accessible to executables which link to the executable compiled from this file*, which can help prevent namespace collisions (at least, I believe that is the purpose). I think this is also the meaning Elysia has in mind WRT to "global" static variables, which would be similarly limited in scope to a single file.

    * or from one file to the next if compiled together
    Last edited by MK27; 06-09-2010 at 11:00 AM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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