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Posted 11 May 2011

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See If a Flags Enum is Valid

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11 May 2011CPOL
This is an alternative to "See If a Flags Enum is Valid".

This alternative probably is less expensive than Andrew's alternate 1; rather than calculating the maximum value the enum can have, it checks each individual bit that is set in the input value, one by one. There is a hack involved, for any non-zero value the expression value & (-value) yields a number that has exactly one bit set, the lowest one that is also set in value.

public static bool IsFlagsValid<T>(int value) {
    Type enumType = typeof(T);
    while (value!=0) {
        int lowestBit=value & (-value);
        if (!Enum.IsDefined(enumType, lowestBit)) return false;
    return true;

There is one limitation: the method's value parameter must have the same type as type T is based on; that is imposed by the IsDefined() method. So one might want to have a second method with long value instead of int value. Maybe, I don't know, this could be remedied by making it even more generic, based on Enum.GetUnderlyingType.



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


About the Author

Luc Pattyn
Software Developer (Senior)
Belgium Belgium
I am an engineer with a background in electronics, software and mathematics.

I develop technical software, both for embedded systems and for desktop equipment. This includes operating systems, communication software, local networks, image processing, machine control, automation, etc.

I have been using all kinds of microcontrollers and microprocessors (Intel 4004/8080/8051/80386/Pentium, Motorola 680x/680x0/ColdFire/PowerPC, Microchip PIC, Altera NIOS, and many more), lots of programming languages (all relevant assemblers, Fortran, Basic, C, Java, C#, and many more), and different operating systems (both proprietary and commercial).

For desktop applications and general development tools I have been using both UNIX systems and Mac/MacOS for many years, but I have switched to x86-based PCs with Windows, Visual Studio and the .NET Framework several years ago.

I specialize in:
- cross-platform development (making software that runs on diverse hardware/OS combinations)
- instruction set simulation
- improving software performance, i.e. making sure the software runs the job at hand in as short a time as possible on the given hardware. This entails algorithm selection, implementation design, accurate measurements, code optimisation, and sometimes implementing virtual machines, applying SIMD technology (such as MMX/SSE), and more.

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