What is the difference between volatile and atomic in C++?

What is the difference between volatile and atomic in C++?

In C++, volatile is a type qualifier that tells the compiler that a variable may be changed by something outside the control of the program, like hardware or a different thread. It prevents the compiler from optimizing the variable, ensuring that every read or write operation accesses the actual memory location.

On the other hand, atomic refers to operations that are performed as a single, indivisible step. This means that when an atomic operation is executed, it cannot be interrupted, ensuring thread safety without the need for locks.

Can you give an example of when to use volatile?

Sure! You would use volatile when dealing with hardware registers in embedded systems. For example, if you're reading a value from a sensor that can change independently of your program's execution, you would declare that variable as volatile to ensure the compiler always fetches the latest value from memory.

And what about atomic? When should I use it?

You should use atomic when you need to perform operations on shared variables in a multithreaded environment. For instance, if multiple threads are incrementing a counter, using std::atomic<int> ensures that each increment operation is safe and won't lead to race conditions.

Are there performance differences between using volatile and atomic?

Yes, there are performance differences. volatile does not provide any synchronization guarantees, so it can lead to race conditions if accessed by multiple threads. atomic, however, provides a way to perform operations safely across threads, but it may introduce some overhead due to the necessary synchronization mechanisms.