When to use volatile

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  1. an object that is a memory-mapped I/O port

  2. an object that is shared between multiple concurrent processes

  3. an object that is modified by an asynchronous signal handler

  4. an automatic storage duration object declared in a function that calls setjmp and whose value is changed between the call to setjmp and a corresponding call to longjmp

For details refer :http://www.programmersheaven.com/articles/pathak/article1.htm

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