Resources For IT Professionals
United States (English) # Introduction​

At first glance converting the datatype (System.Decimal) to and from bytes may appear to be a challenge, this is because the BitConverter and Convert classes do not have methods to convert decimals to and from bytes with. The decimal data type has built in methods for converting, although they are somewhat obscure. Here are two simple functions for converting decimals to a list of bytes, and then back to a decimal (at the end of the article).

## Getting the bytes of a System.Decimal

You may have noticed or not, but the Decimal class has a shared method called "GetBits". This method will return an array containing four 32 bit integers, so not quite the bits you would be expecting. So at first you might be expecting those four integers to be one's or zero's. This is not the case. The bits of the decimal are actually extrapolated by taking the bytes of those four 32 bit integers (4*32=128). This means that a decimal is a 128 bit (16 bytes) structure.

## Creating an instance of the System.Decimal from bytes

So you may have been in a place where you were pulling your hair out trying to figure out how to get an instance of System.Decimal from those bytes. This is because you may be used to creating instances of numeric datatypes using the BitConverter class or the Convert class. The BitConverter & Convert classes do not have any methods built in to support the Decimal datatype. So this may seem like a really confusing problem at first, but the truth is that the Decimal class has a constructor that accepts an array of exactly four 32 bit integers as a parameter.

# Summary

So in a nutshell, this means that you can take your binary information using the Decimal.GetBits function, save it to your file, or whatever you need to do. You can later then load those bytes into an array, convert those bytes into integers, put those integers into another array, and finally, pass that array of integers to the decimal's constructor sub.

Code Examples

Visual Basic
```'Prevent simple errors with options ```
`Option` `Strict ``On`
`Option` `Explicit ``On`
`Option` `Infer Off `
`Public` `Class` ``` Form1 ```
`    ``Private` `Sub` ``` Button1_Click(sender ````As` `Object````, e ````As` ``` EventArgs) ````Handles` ``` Button1.Click ```
`        ````'create a decimal for testing ```
`        ``Dim` `testDecimal ``As` `Decimal` ``` = 987.123456D ```
`        ````'Get the bytes of the decimal ```
`        ``Dim` `decimalBytes ``As` `Byte````() = BitconverterExt.GetBytes(testDecimal) ```
`        ````'Create a decimal from those bytes ```
`        ``Dim` `fromBytes ``As` `Decimal` ``` = BitconverterExt.ToDecimal(decimalBytes) ```
`        ````'Display the result ```
`        ````MsgBox(fromBytes.ToString) ```
`    ``End` `Sub`
`End` `Class`
`Public` `Class` ``` BitconverterExt ```
`    ``Public` `Shared` ``` Function``` `GetBytes(dec ``As` `Decimal````) ````As` ``` Byte````() `
`        ````'Load four 32 bit integers from the Decimal.GetBits function ```
`        ``Dim` `bits ``As` `Int32() = ``Decimal````.GetBits(dec) ```
`        ````'Create a temporary list to hold the bytes ```
`        ``Dim` `bytes ``As` `New` ``` List(Of ````Byte````) ```
`        ````'iterate each 32 bit integer ```
`        ``For` `Each` ``` i ````As` ``` Int32 ````In` ``` bits ```
`            ````'add the bytes of the current 32bit integer ```
`            ````'to the bytes list ```
`            ````bytes.AddRange(BitConverter.GetBytes(i)) ```
`        ``Next`
`        ````'return the bytes list as an array ```
`        ``Return` `bytes.ToArray `
`    ``End` `Function`
`    ``Public` `Shared` ``` Function``` `ToDecimal(bytes ``As` `Byte````()) ````As` ``` Decimal```
`        ````'check that it is even possible to convert the array ```
`        ``If` `bytes.Count <> 16 ``Then` `Throw` ``` New``` `Exception(``"A decimal must be created from exactly 16 bytes"````) ```
`        ````'make an array to convert back to int32's ```
`        ``Dim` `bits(3) ``As` `Int32 `
`        ``For` `i ``As` `Integer` ``` = 0 ````To` ``` 15 ````Step` ``` 4 ```
`            ````'convert every 4 bytes into an int32 ```
`            ````bits(i \ 4) = BitConverter.ToInt32(bytes, i) ```
`        ``Next`
`        ````'Use the decimal's new constructor to ```
`        ````'create an instance of decimal ```
`        ``Return` `New` ``` Decimal````(bits) `
`    ``End` `Function`
`End` `Class`

C#

`using` `System; `
`using` `System.Collections.Generic; `
`using` `System.ComponentModel; `
`using` `System.Data; `
`using` `System.Drawing; `
`using` `System.Linq; `
`using` `System.Text; `
`using` `System.Threading.Tasks; `
`using` `System.Windows.Forms; `
`namespace` `WindowsFormsApplication1 `
```{ ```
`    ``public` `partial` ``` class``` `Form1 : Form `
`    ````{ ```
`        ``public` `Form1() `
`        ````{ ```
`            ````InitializeComponent(); ```
`        ````} ```
`        ``private` `void` ``` Form1_Load(````object` ``` sender, EventArgs e){} ```
`        ``private` `void` ``` button1_Click(````object` ``` sender, EventArgs e) ```
`        ````{ ```
`            ````//create a decimal for testing ```
`            ``decimal` `testDecimal = 987.123456m; `
`            ````//Get the bytes of the decimal ```
`            ``byte````[] decimalBytes = BitconverterExt.GetBytes(testDecimal); ```
`            ````//Create a decimal from those bytes ```
`            ``decimal` `fromBytes = BitconverterExt.ToDecimal(decimalBytes); `
`            ````//Display the result ```
`           ````MessageBox .Show(fromBytes.ToString()); ```
`        ````} ```
`    ````} ```
`    ``public` `class` ``` BitconverterExt ```
`    ````{ ```
`           ``public` `static` ``` byte````[] GetBytes(``decimal` `dec) `
`        ````{ ```
`            ````//Load four 32 bit integers from the Decimal.GetBits function ```
`            ````Int32[] bits = ````decimal````.GetBits(dec); ```
`            ````//Create a temporary list to hold the bytes ```
`            ``List<``byte````> bytes = ````new` ``` List<````byte````>(); ```
`            ````//iterate each 32 bit integer ```
`            ``foreach` `(Int32 i ``in` `bits) `
`            ````{ ```
`                ````//add the bytes of the current 32bit integer ```
`                ````//to the bytes list ```
`                ````bytes.AddRange(BitConverter.GetBytes(i)); ```
`            ````} ```
`            ````//return the bytes list as an array ```
`            ``return` `bytes.ToArray(); `
`        ````} ```
`        ``public` `static` ``` decimal``` `ToDecimal(``byte````[] bytes) ```
`        ````{ ```
`            ````//check that it is even possible to convert the array ```
`            ``if` `(bytes.Count() != 16) `
`                ``throw` `new` ``` Exception(````"A decimal must be created from exactly 16 bytes"````); ```
`            ````//make an array to convert back to int32's ```
`            ````Int32[] bits = ````new` ``` Int32; ```
`            ``for` `(``int` `i = 0; i <= 15; i += 4) `
`            ````{ ```
`                ````//convert every 4 bytes into an int32 ```
`                ````bits[i/4] = BitConverter.ToInt32(bytes, i); ```
`            ````} ```
`            ````//Use the decimal's new constructor to ```
`            ````//create an instance of decimal ```
`            ``return` `new` ``` decimal````(bits); `
`        ````} ```
`    ````} ```
`}`

## References

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