25.2. const_cast Operator

C++ provides the const_cast operator for casting away const or volatile qualification. You declare a variable with the volatile qualifier when you expect the variable to be modified by hardware or other programs not known to the compiler. Declaring a variable volatile indicates that the compiler should not optimize the use of that variable because doing so could affect the ability of those other programs to access and modify the volatile variable.

In general, it is dangerous to use the const_cast operator, because it allows a program to modify a variable that was declared const, and thus was not supposed to be modifiable. There are cases in which it is desirable, or even necessary, to cast away const-ness. For example, older C and C++ libraries might provide functions that have non-const parameters and that do not modify their parameters. If you wish to pass const data to such a function, you would need to cast away the data’s const-ness; otherwise, the compiler would report error messages.