C Quiz – 107 | Question 4

Pick the correct statement for const and volatile.
(A) const is the opposite of volatile and vice versa.
(B) const and volatile can’t be used for struct and union.
(C) const and volatile can’t be used for enum.
(D) const and volatile can’t be used for typedef.
(E) const and volatile are independent i.e. it’s possible that a variable is defined as both const and volatile.

Answer: (E)
Explanation: In C, const and volatile are type qualifiers and these two are independent. Basically, const means that the value isn’t modifiable by the program. And volatile means that the value is subject to sudden change (possibly from outside the program). In fact, C standard mentions an example of valid declaration which is both const and volatile. The example is “extern const volatile int real_time_clock;” where real_time_clock may be modifiable by hardware, but cannot be assigned to, incremented, or decremented. So we should already treat const and volatile separately. Besides, these type qualifier applies for struct, union, enum and typedef as well.
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