C volatile Keyword: Usage Explained

In the C language, the keyword “volatile” is used to inform the compiler that the value of a variable may be changed outside of the program’s control, so the compiler should not optimize this variable. The value of a volatile variable may be altered by external factors such as hardware interrupts, multi-threaded operations, etc., so the compiler must always read the value of the volatile variable from memory each time it is accessed, instead of from a register.

The volatile keyword is commonly used to describe hardware registers or shared data, ensuring their correct access in multi-threaded or interrupt environments.

In the C language, the method of declaring a variable as volatile is to add the keyword volatile before the variable type, for example:

volatile int x;

By making this declaration, the compiler will understand that operations on variable x need to read the value from memory each time, without any optimization.