Can a variable be both const and volatile?

Can a Variable be Both Const and Volatile? Exploring the Intersection of Two C Keywords

Yes, a variable can be declared as both const and volatile in C or C++.

Declaring a variable as const means that its value cannot be modified in the program, while declaring it as volatile means that the variable's value may change at any time, even if there are no statements in the code that explicitly modify it.

The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code. For instance, in the example in FAQ 8, the timer structure was accessed through a volatile const pointer. The function itself did not change the value of the timer, so it was declared const. However, the value was changed by hardware on the computer, so it was declared volatile. If a variable is both const and volatile, the two modifiers can appear in either order.

For example, consider the following code snippet:

const volatile int x = 10;

In this case, x is declared as const to ensure that its value cannot be modified, and volatile is used to indicate to the compiler that the value of x might change unexpectedly, so it should not be optimized away.

Note that the order of the keywords does not matter, i.e., volatile const int x = 10; would have the same effect as the previous example.