Convert decimal? to double?

Question

I am wondering what would be the best way (in the sense of safer and succinct) to convert from one nullable type to another "compatible" nullable type.

Specifically, converting from decimal? to double? can be done using:

public double? ConvertToNullableDouble(decimal? source)
{
    return source.HasValue ? Convert.ToDouble(source) : (double?) null;
}

Is there any better way to do this? Maybe leveraging a standard conversion?

You are doing it right! Check also this reference: http://stackoverflow.com/questions/5487685/conversion-between-nullable-types — MUG4N, May 02 '13 at 21:20

Avner Shahar-Kashtan · Accepted Answer · 2013-05-02T21:23:07.350

38

Built in casts for the win! Just tested this in VS2012 and VS2010:

 decimal? numberDecimal = new Decimal(5); 
 decimal? nullDecimal = null;
 double? numberDouble = (double?)numberDecimal; // = 5.0
 double? nullDouble = (double?)nullDecimal;     // = null

Just using an explicit cast will cast null to null, and the internal decimal value to double. Success!

edited May 02 '13 at 21:23

answered May 02 '13 at 21:14

Avner Shahar-Kashtan

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Tested it and works like a charm. Thanks, this was what I was looking for but I didn't think of a built in cast. – Camilo Martinez May 02 '13 at 21:33
It's strange, since in questions like the one MUG4N linked to it seems a lot of people have theories, but no-one actually *tried*. :) – Avner Shahar-Kashtan May 02 '13 at 21:35
2

In fact *all* conversions that involve a non-nullable value type source and target may be "lifted to nullable". – Eric Lippert May 03 '13 at 05:52
@EricLippert That's strange, since I could see an *explicit* conversion to the non-nullable type, but not an implicit one. – Avner Shahar-Kashtan May 03 '13 at 06:33
@AvnerShahar-Kashtan: The conversion from decimal to double is explicit, so the conversion from decimal? to double? is also. – Eric Lippert May 03 '13 at 14:40
1

Just as information: it works based on my experience in the other direction as well. I mean converting a nullable double to a nullable decimal. – pholpar Aug 09 '17 at 12:13

diwatu · Answer 2 · 2013-05-02T22:01:13.943

1

In general, if you want o convert from any data type to the other as long as they are compatible, use this:

    Convert.ChangeType(your variable, typeof(datatype you want convert to));

for example:

    string str= "123";
    int value1 = (int)Convert.ChangeType(str, typeof(int));
    float? value2 = (float?)Convert.ChangeType(str, typeof(float));
    ...................................

A little bit further, if you want it to be more safer, you can add a try catch on it:

string str= "123";
try
{
    int value1 = (int)Convert.ChangeType(str, typeof(int));
    int? value2 = (int?)Convert.ChangeType(str, typeof(int));
    float value3 = (float)Convert.ChangeType(str, typeof(float));
    float? value4 = (float?)Convert.ChangeType(str, typeof(float));
}
catch(Exception ex)
{
  // do nothing, or assign a default value
}

this is tested under VS 2010

edited May 02 '13 at 22:01

answered May 02 '13 at 21:28

diwatu

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Yes, this is a more general way to convert between types, not as succinct as the accepted answer. @Giswin Does it works for nullables as well? I imagine so, but I don't find a specific comment on this in the [documentation](http://msdn.microsoft.com/en-us/library/dtb69x08.aspx). – Camilo Martinez May 02 '13 at 21:35
you can use this: decimal? v1 =222; double? V2 = (double?)Convert.ChangeType(v1, typeof(double)); but if v1 is null, Convert.ChangeType will throw a exception. and then the try catch dose the left job. – diwatu May 02 '13 at 21:51

Convert decimal? to double?

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