How to check if enum value is valid?

Question

I am reading an enum value from a binary file and would like to check if the value is really part of the enum values. How can I do it?

#include <iostream>  enum Abc {     A = 4,     B = 8,     C = 12 };  int main() {     int v1 = 4;     Abc v2 = static_cast< Abc >( v1 );      switch ( v2 )     {         case A:             std::cout<<"A"<<std::endl;             break;         case B:             std::cout<<"B"<<std::endl;             break;         case C:             std::cout<<"C"<<std::endl;             break;         default :             std::cout<<"no match found"<<std::endl;     } } 

Do I have to use the switch operator or is there a better way?

EDIT

I have enum values set and unfortunately I can not modify them. To make things worse, they are not continuous (their values goes 0, 75,76,80,85,90,95,100, etc.)

Answer 1

enum value is valid in C++ if it falls in range [A, B], which is defined by the standard rule below. So in case of enum X { A = 1, B = 3 }, the value of 2 is considered a valid enum value.

Consider 7.2/6 of standard:

For an enumeration where emin is the smallest enumerator and emax is the largest, the values of the enumeration are the values of the underlying type in the range bmin to bmax, where bmin and bmax are, respectively, the smallest and largest values of the smallest bit-field that can store emin and emax. It is possible to define an enumeration that has values not defined by any of its enumerators.

There is no retrospection in C++. One approach to take is to list enum values in an array additionally and write a wrapper that would do conversion and possibly throw an exception on failure.

See Similar Question about how to cast int to enum for further details.

Answer 2

Maybe use enum like this:

enum MyEnum { A, B, C }; 

and to check

if (v2 >= A && v2 <= C) 

If you don't specify values for enum constants, the values start at zero and increase by one with each move down the list. For example, given enum MyEnumType { ALPHA, BETA, GAMMA }; ALPHA has a value of 0, BETA has a value of 1, and GAMMA has a value of 2.