Noah - 3 months ago 34

C# Question

I'm trying to validate that a decimal in c# will fit into a db column decimal. The SqlDecimal object allows you to pass in a precision and scale as well as the decimal bits to the constructor. I know the size of the column and so before we write the data I check each input so I can produce business required output.

In this case we are storing a percent, so the precision is **13** and the scale is **10**. I have a testing harness that I've condensed below into a unti test for SO. This sample is throwing an Arithmetic Overflow error on the SqlDecimal constructor line:

`[TestMethod]`

public void TestDecimalFits()

{

decimal d = 10.3m;

SqlDecimal sqlDecimal = new SqlDecimal(13, 10, d >= 0, Decimal.GetBits(d));

Assert.AreEqual(d, sqlDecimal.Value);

}

Does anyone know why this blows up?

Thanks!

Answer

The return of `Decimal.GetBits`

is not compatible with the `SqlDecimal`

's constructor parameter.

`Decimal.GetBits`

returns an array that represents the exact structure of the decimal, which includes the 96-bit scaled integer value and 8 bits for the exponent (plus 1 sign bit and 27 unused bits).

The `SqlDecimal`

constructor that you are using takes an `int`

array that represents "The 128-bit unsigned integer that provides the value of the new SqlDecimal." - NOT the *represenatation* of that decimal value. The `scale`

parameter determines what the *actual* value of the decimal will be.

So you are effectively passing in a different value than the constructor expects. The .NET decimal equivalent of 10.3m is

```
0000000001100111-0000000000000000-0000000000000000-10000000000000000
```

Where `1100111`

is the binary equivalent of 103, and `1`

is the scale.

The integer equivalent of that binary value is more than 13 digits long, which is why you get an overflow when passing it to the SqlDecimal constructor.

I would not play around with bit-fiddling and instead just use the raw `decimal`

value, letting SQL convert it to the right precision and scale automatically.

I'm trying to validate that a decimal in c# will fit into a db column decimal.

Well, the largest value that will fit into a `DECIMAL(13,10)`

is `999.9999999999`

, which is well below the maximum value of a `decimal`

. So no, you can't stire *any* C# decimal value in a `DECIMAL(13,10)`

SQL column.

(technically I think you can store `9999999999999`

by dropping the precision, but even that is well below the maximum value of a `decimal`

).