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See if a Flags enum is valid

, 10 May 2011 CPOL
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See if an integer value is a valid value for the given "flags" enumerator
Let's say you have an enumerator defined like so:
 
[Flags]
public MyFlags { None=0, One=1, Eight=8 };
 
The following method can be used to see if a given integer value is a valid combination of one or more of the ordinal values:
 
bool IsFlagsValid(Type enumType, int value)
{
    bool valid = false;
    if (enumType.IsEnum)
    {
        valid = true;
        int maxBit = Convert.ToInt32(Math.Pow(2, Math.Ceiling(Math.Log(value)/Math.Log(2)))) >> 2;
        int i = 1;
        do
        {
            int ordinalValue = (1 << i);
            if (0 != (value & ordinalValue))
            {
                valid = (Enum.IsDefined(enumType, ordinalValue));
                if (!valid)
                {
                    break;
                }
            }
            i++;
        } while (maxBit > i);
    }
    return valid;
} 
 
Calling the method with any value other than 0, 1, 8, and 9 would return false. For instance, the following would return false:
 
if (IsFlagsValid(MyFlags, 25))
{
    // do something if the value was valid
}

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

John Simmons / outlaw programmer
Software Developer (Senior)
United States United States
I've been paid as a programmer since 1982 with experience in Pascal, and C++ (both self-taught), and began writing Windows programs in 1991 using Visual C++ and MFC. In the 2nd half of 2007, I started writing C# Windows Forms and ASP.Net applications, and have since done WPF, Silverlight, WCF, web services, and Windows services.
 
My weakest point is that my moments of clarity are too brief to hold a meaningful conversation that requires more than 30 seconds to complete. Thankfully, grunts of agreement are all that is required to conduct most discussions without committing to any particular belief system.

Comments and Discussions

 
GeneralLeftshifting could fail Pinmemberleppie11-May-11 2:11 

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