CODEWITHSUNDEEP
c#.netreflectionconstants
Fraser
Fraser

Reputation: 17059

Determine the name of a constant based on the value

Is there a way of determining the name of a constant from a given value?

For example, given the following:

public const uint ERR_OK = 0x00000000;

How could one obtain "ERR_OK"?

I have been looking at refection but cant seem to find anything that helps me.

Upvotes: 6

Views: 12195

Answers (7)

Yohan
Yohan

Reputation: 400

I may be late.. but i think following could be the answer

public static class Names
    {
        public const string name1 = "Name 01";
        public const string name2 = "Name 02";

        public static string GetName(string code)
        {
            foreach (var field in typeof(Names).GetFields())
            {
                if ((string)field.GetValue(null) == code)
                    return field.Name.ToString();
            }
            return "";
        }
    }

and following will print "name1"

string result = Names.GetName("Name 01");
Console.WriteLine(result )

Upvotes: 4

Jon Skeet
Jon Skeet

Reputation: 1500615

In general, you can't. There could be any number of constants with the same value. If you know the class which declared the constant, you could look for all public static fields and see if there are any with the value 0, but that's all. Then again, that might be good enough for you - is it? If so...

public string FindConstantName<T>(Type containingType, T value)
{
    EqualityComparer<T> comparer = EqualityComparer<T>.Default;

    foreach (FieldInfo field in containingType.GetFields
             (BindingFlags.Static | BindingFlags.Public))
    {
        if (field.FieldType == typeof(T) &&
            comparer.Equals(value, (T) field.GetValue(null)))
        {
            return field.Name; // There could be others, of course...
        }
    }
    return null; // Or throw an exception
}

Upvotes: 15

Iain Hoult
Iain Hoult

Reputation: 4005

The easiest way would be to switch to using an enum

Upvotes: 0

Nick
Nick

Reputation: 3337

I suggest you use an enum to represent your constant.

Or

string ReturnConstant(uint val)
{
     if(val == 0x00000000)
       return "ERR_OK";
     else
       return null;
}

Upvotes: 0

foson
foson

Reputation: 10227

You may be interested in Enums instead, which can be programmatically converted from name to value and vice versa.

Upvotes: 3

Matthew Groves
Matthew Groves

Reputation: 26151

I don't think you can do that in a deterministic way. What if there are multiple constants with the same value?

Upvotes: 0

Andrew Hare
Andrew Hare

Reputation: 351516

You won't be able to do this since constants are replaced at compilation time with their literal values.

In other words the compiler takes this:

class Foo
{
    uint someField = ERR_OK;
}

and turns it into this:

class Foo
{
    uint someField = 0;
}

Upvotes: 2

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