What makes a variable volatile?

A variable should be declared volatile whenever its value could change unexpectedly. In practice, only three types of variables could change: Memory-mapped peripheral registers. Global variables modified by an interrupt service routine.

Where volatile variables are stored?

There’s no reason for a volatile variable to be stored in any “special” section of memory. It is normally stored together with any other variables, including non-volatile ones. If some compiler decides to store volatile variables in some special section of memory – there’s nothing to prevent it from doing so.

Is volatile a variable?

What Does Volatile Variable Mean? A volatile variable is a variable that is marked or cast with the keyword “volatile” so that it is established that the variable can be changed by some outside factor, such as the operating system or other software.

Is volatile atomic in C?

Firstly, volatile does not imply atomic access. It is designed for things like memory mapped I/O and signal handling. volatile is completely unnecessary when used with std::atomic , and unless your platform documents otherwise, volatile has no bearing on atomic access or memory ordering between threads.

What happens when a variable is marked as volatile?

When we declare a variable volatile, it means that all reads and all writes to this variable or from this variable will go directly into the main memory. The values of these variables will never be cached.

Which of the following variable is volatile?

Discussion Forum

Why is volatile needed?

The volatile field is needed to make sure that multiple threads always see the newest value, even when the cache system or compiler optimizations are at work. Reading from a volatile variable always returns the latest written value from this variable.

What is volatile keyword?

The volatile keyword prevents the compiler from performing optimization on code involving volatile objects, thus ensuring that each volatile variable assignment and read has a corresponding memory access.

Does atomic imply volatile?

Relationship with volatile In addition, volatile accesses are not atomic (concurrent read and write is a data race) and do not order memory (non-volatile memory accesses may be freely reordered around the volatile access).