Take a string to a byte[]

I have a string in my database that represents an image. It looks like this:

0x89504开发者_JS百科E470D0A1A0A0000000D49484452000000F00000014008020000000D8A66040....
<truncated for brevity>

When I load it in from the database it comes in as a byte[]. How can I convert the string value to a byte array myself. (I am trying to remove the db for some testing code.)

class Program
{
    static void Main()
    {
        byte[] bytes = StringToByteArray("89504E470D0A1A0A0000000D49484452000000");
    }

    public static byte[] StringToByteArray(string hex)
    {
        int length = hex.Length;
        byte[] bytes = new byte[length / 2];
        for (int i = 0; i < length; i += 2)
            bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
        return bytes;
    }
}

It sounds like you're asking how to convert a string with a particular encoding to a byte array.

If so, it depends on how the string is encoded. For example, if you have a base64 encoded string, then you could get a byte array using:

asBytes = System.Text.Encoding.UTF8.GetBytes(someString);

If the encoding is hexadecimal (as it appears to be in your example) there's nothing built into the BCL, but you could use LINQ (just remove the 0x at the head of the string first):

public static byte[] StringToByteArray(string hex) { 
    return Enumerable.Range(0, hex.Length). 
        Where(x => 0 == x % 2). 
        Select(x => Convert.ToByte(hex.SubString(x,2), 16)). 
        ToArray(); 
} 

I believe you're actually trying to convert the hexadecimal number to a byte array.

If so, you can do it like this: (Remove the 0x first)

var bytes = new byte[str.Length / 2];
for(int i = 0; i < str.Length; i += 2)
    bytes[i / 2] = Convert.ToByte(str.Substring(i, 2), 16);

(Tested)

If it comes in as a byte[], then it's not a string.

What is the column data type? Varbinary?

String in .NET means “text” – there’s a fundamental difference to a byte array and no 1:1 mapping exists (just as for other complex .NET types).

In particular, a string is encoded in an appropriate character encoding. As has already been posted, a given text can be decoded into a desired byte representation. In your particular case, it looks as though you’ve got a individual bytes represented as padded hexadecimal numbers, i.e. every byte is two characters wide:

int bytelength = (str.Length - 2) / 2;
byte[] result = new byte[byteLength]; // Take care of leading "0x"
for (int i = 0; i < byteLength; i++)
    result[i] = Convert.ToByte(str.Substring(i * 2 + 2, 2), 16);

String to Byte Array Conversion in C#
http://www.chilkatsoft.com/faq/dotnetstrtobytes.html