Asked by: Shiyong Ndiaye
technology and computing programming languages

Can we use static and volatile together in C?

Last Updated: 1st April, 2021

Static variables retain their value betweenfunction calls. Volatile variables (which is not theopposite of static) are used when a variable isused both within an ISR (interrupt service routine) andoutside it. Volatile tells the compiler to always load avariable from RAM rather than caching it in a CPUregister.

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Keeping this in view, can we use static and volatile together?

Even if you access a static value throughmultiple threads, each thread can have its local cachedcopy! To avoid this you can declare the variable asstatic volatile and this will force the thread toread each time the global value. However, volatile is not asubstitute for proper synchronisation!

Secondly, why do we use volatile in C? C's volatile keyword is a qualifier that isapplied to a variable when it is declared. It tells the compilerthat the value of the variable may change at any time--without anyaction being taken by the code the compiler finds nearby. Theimplications of this are quite serious.

Similarly one may ask, what does static volatile mean in C?

static refers to the scope of the variable. Ifthe variable is global, it means that the scope is limited to thesource file it was declared in. If the variable is local to afunction, then it means the memory used to hold this variable is inthe application's statically allocated memory.

Can we use const with volatile in C?

Yes. A variable can be declared as bothvolatile and constant in C. Constmodifier does not allow changing the value of the variable byinternal program. But, it does not mean that value of constvariable should not be changed by external code.

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