register keyword in C?

Question

What does the `register` keyword do in C language? I have read that it is used for optimizing but is not clearly defined in any standard. Is it still relevant and if so, when would you use it?

Answer 1

'Register' is a command to instruct that the associated value is to be stored in a register rather than memory. Since most operations are carried out using registers, by specifying the value be kept in one it ensures the value is available in the least possible amount of time.