What is the use of volatile keyword in C?

What is the use of volatile keyword in C?

• A. To define a variable that cannot be modified
• B. To optimize the memory usage of variables
• C. To prevent optimization on a variable that may change unexpectedly
• D. To declare a constant variable

Answer: (C)

The volatile keyword in C is used to indicate that a variable's value may change at any time without any action being taken by the code the compiler finds nearby. This is particularly important when dealing with hardware, signal handlers, or threads, where the variable can be modified by external factors outside the program's control. By marking a variable as volatile, the compiler is instructed not to optimize accesses to that variable, ensuring that every read or write operation directly accesses the memory instead of using a cached value. This behavior is crucial in scenarios where a variable's state can change asynchronously, such as in embedded programming where the variable might reflect a hardware status flag, or in multithreading contexts where one thread might update the variable while another reads it. The other options do not accurately represent the function of the volatile keyword: it does not prevent modification of the variable, optimize memory usage, or declare constants. Instead, it specifically addresses the need for the compiler to always fetch the current value of a variable that is expected to change beyond the control of the program logic.

The volatile keyword in C is used to indicate that a variable's value may change at any time without any action being taken by the code the compiler finds nearby. This is particularly important when dealing with hardware, signal handlers, or threads, where the variable can be modified by external factors outside the program's control. By marking a variable as volatile, the compiler is instructed not to optimize accesses to that variable, ensuring that every read or write operation directly accesses the memory instead of using a cached value.

This behavior is crucial in scenarios where a variable's state can change asynchronously, such as in embedded programming where the variable might reflect a hardware status flag, or in multithreading contexts where one thread might update the variable while another reads it.

The other options do not accurately represent the function of the volatile keyword: it does not prevent modification of the variable, optimize memory usage, or declare constants. Instead, it specifically addresses the need for the compiler to always fetch the current value of a variable that is expected to change beyond the control of the program logic.