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Static can be applied to a variable to expand it's scope beyond a single routine.<br />
It forces file allocation from the heap instead of the stack, so the variable will persist beyond the execution of the routine. The programmer must assign an initial value, and at the next pass through the routine it will retain its last value. It is also available to reference throughout all routines in a single module (file scope).<br />
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Volatile can be applied to a variable to imply its value may change asynchronously (as in a multi-threaded environment). This warns the compiler that it can't generate code that assumes a value just because it hasn't changed locally. Usually, it restricts code optimizers that might make erroneous assumptions about values based only on the code it &quot;sees.&quot;
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The part of n2fc's post on the 'static' keyword is not entirely accurate/complete.<br />
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The 'static' keyword can be used for two different purposes, neither of which change the scope of the symbol the keyword is applied to.<br />
The first usage of the 'static' keyword, is when it is used with a file-scope identifier. In that case, the identifier has internal linkage (ie. it can only be accessed from the compilation unit where it has been defined).<br />
The second usage of the 'static' keyword, is when it is used for an object. In that case, the identifier has static storage duration (ie. its lifetime is the entire execution of the program).<br />
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The 'volatile' keyword is a type qualifier that indicates to the compiler that the object can be changed in ways unknown to the compiler (and outside of its control). It prevents the compiler from making certain assumptions (for optimizations eg.) that would get in the way of these external modifications.
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&gt;&gt; &nbsp;In one use, 'static' controls scope<br />
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It never controls the scope. Which was kind of the point I was trying to make in my previous post ;) It can control the linkage and the storage duration, but that's it.
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Since eager's post was expanding on what I said, it would have been nice if my post was included in the PAQ too. Moreover, the accepted post is not 100% accurate, as my previous post explains.
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Can anybody explain me static and volatile keywords in C, and when to use them.<br />
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Thanks
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Can anybody explain me static and volatile keywords in C, and when to use them.

Thanks

STATIC AND VOLATILE IN C

C is a general-purpose, imperative computer programming language, supporting structured programming, lexical variable scope and recursion, while a static type system prevents many unintended operations. By design, C provides constructs that map efficiently to typical machine instructions, so it has found lasting use in applications that had formerly been coded in assembly language, including operating systems as well as various application software for computers ranging from supercomputers to embedded systems. It is distinct from C++ (which has its roots in C) and C#, and many later languages have borrowed directly or indirectly from C.

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