In reply to rohitk:
Section 6.24.1 Cast operator says
An expression may be changed to a constant with a const cast.
const'(x)
When casting an expression as a constant, the type of the expression to be cast shall pass through unchanged.
The only effect is to treat the value as though it had been used to define a const variable of the type of the
expression.
Basically it’s like a sampled value at the point of evaluation of the expression.