Difference Betn Volatile,static,extern variables

This is a discussion on Difference Betn Volatile,static,extern variables within the C Programming forums, part of the General Programming Boards category; hi, Can somebody explain me exact difference between volatile ,static and extern variables. when to use these variables?I know use ...

  1. #1
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    Smile Difference Betn Volatile,static,extern variables

    hi,
    Can somebody explain me exact difference between volatile ,static and extern variables.
    when to use these variables?I know use of extern but dont know diff betn extern and volatile.
    please give me a small example which is using volatile variable.

    Thank You,
    Nitin

  2. #2
    and the hat of wrongness Salem's Avatar
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    What does your C book have to say about them?

    static and extern are to do with scope.
    - extern - somewhere else
    - static - local to this module

    volatile and const are to do with how the value can be changed.
    - const means diagnose attempts to modify the variable
    - volatile means that the compiler should not assume the variable maintains it's value between reads of that variable.

    > please give me a small example which is using volatile variable.
    extern const volatile int clock;
    Now you tell me what you think that means.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    extern const volatile int clock;
    this means clock is defined as volatile somewhere else i.e in other source and its value could get changed by some external process(program) whose control is not under our program.

    The const volatile keyword is confusing me,please give me explaination,if my above description is wrong.

  4. #4
    and the hat of wrongness Salem's Avatar
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    Well if volatile wasn't there, would you know what const means?

    It means the same thing if you put volatile in there.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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