How do I get a consistent byte representation of s

Question

How do I convert a string to a byte[] in .NET (C#) without manually specifying a specific encoding?

I'm going to encrypt the string. I can encrypt it without converting, but I'd still like to know why encoding comes to play here.

Also, why should encoding be taken into consideration? Can't I simply get what bytes the string has been stored in? Why is there a dependency on character encodings?

Answer 1

Here is my unsafe implementation of String to Byte[] conversion:

public static unsafe Byte[] GetBytes(String s)
{
    Int32 length = s.Length * sizeof(Char);
    Byte[] bytes = new Byte[length];

    fixed (Char* pInput = s)
    fixed (Byte* pBytes = bytes)
    {
        Byte* source = (Byte*)pInput;
        Byte* destination = pBytes;

        if (length >= 16)
        {
            do
            {
                *((Int64*)destination) = *((Int64*)source);
                *((Int64*)(destination + 8)) = *((Int64*)(source + 8));

                source += 16;
                destination += 16;
            }
            while ((length -= 16) >= 16);
        }

        if (length > 0)
        {
            if ((length & 8) != 0)
            {
                *((Int64*)destination) = *((Int64*)source);

                source += 8;
                destination += 8;
            }

            if ((length & 4) != 0)
            {
                *((Int32*)destination) = *((Int32*)source);

                source += 4;
                destination += 4;
            }

            if ((length & 2) != 0)
            {
                *((Int16*)destination) = *((Int16*)source);

                source += 2;
                destination += 2;
            }

            if ((length & 1) != 0)
            {
                ++source;
                ++destination;

                destination[0] = source[0];
            }
        }
    }

    return bytes;
}

It's way faster than the accepted anwser's one, even if not as elegant as it is. Here are my Stopwatch benchmarks over 10000000 iterations:

[Second String: Length 20]
Buffer.BlockCopy: 746ms
Unsafe: 557ms

[Second String: Length 50]
Buffer.BlockCopy: 861ms
Unsafe: 753ms

[Third String: Length 100]
Buffer.BlockCopy: 1250ms
Unsafe: 1063ms

In order to use it, you have to tick "Allow Unsafe Code" in your project build properties. As per .NET Framework 3.5, this method can also be used as String extension:

public static unsafe class StringExtensions
{
    public static Byte[] ToByteArray(this String s)
    {
        // Method Code
    }
}

Answer 2

The first part of your question (how to get the bytes) was already answered by others: look in the System.Text.Encoding namespace.

I will address your follow-up question: why do you need to pick an encoding? Why can't you get that from the string class itself?

The answer is in two parts.

First of all, the bytes used internally by the string class don't matter, and whenever you assume they do you're likely introducing a bug.

If your program is entirely within the .Net world then you don't need to worry about getting byte arrays for strings at all, even if you're sending data across a network. Instead, use .Net Serialization to worry about transmitting the data. You don't worry about the actual bytes any more: the Serialization formatter does it for you.

On the other hand, what if you are sending these bytes somewhere that you can't guarantee will pull in data from a .Net serialized stream? In this case you definitely do need to worry about encoding, because obviously this external system cares. So again, the internal bytes used by the string don't matter: you need to pick an encoding so you can be explicit about this encoding on the receiving end, even if it's the same encoding used internally by .Net.

I understand that in this case you might prefer to use the actual bytes stored by the string variable in memory where possible, with the idea that it might save some work creating your byte stream. However, I put it to you it's just not important compared to making sure that your output is understood at the other end, and to guarantee that you must be explicit with your encoding. Additionally, if you really want to match your internal bytes, you can already just choose the Unicode encoding, and get that performance savings.

Which brings me to the second part... picking the Unicode encoding is telling .Net to use the underlying bytes. You do need to pick this encoding, because when some new-fangled Unicode-Plus comes out the .Net runtime needs to be free to use this newer, better encoding model without breaking your program. But, for the moment (and forseeable future), just choosing the Unicode encoding gives you what you want.

It's also important to understand your string has to be re-written to wire, and that involves at least some translation of the bit-pattern even when you use a matching encoding. The computer needs to account for things like Big vs Little Endian, network byte order, packetization, session information, etc.

Answer 3

Fastest way

public static byte[] GetBytes(string text)
{
    return System.Text.ASCIIEncoding.UTF8.GetBytes(text);
}

EDIT as Makotosan commented this is now the best way:

Encoding.UTF8.GetBytes(text)

Answer 4

BinaryFormatter bf = new BinaryFormatter();
byte[] bytes;
MemoryStream ms = new MemoryStream();

string orig = "喂 Hello 谢谢 Thank You";
bf.Serialize(ms, orig);
ms.Seek(0, 0);
bytes = ms.ToArray();

MessageBox.Show("Original bytes Length: " + bytes.Length.ToString());

MessageBox.Show("Original string Length: " + orig.Length.ToString());

for (int i = 0; i < bytes.Length; ++i) bytes[i] ^= 168; // pseudo encrypt
for (int i = 0; i < bytes.Length; ++i) bytes[i] ^= 168; // pseudo decrypt

BinaryFormatter bfx = new BinaryFormatter();
MemoryStream msx = new MemoryStream();            
msx.Write(bytes, 0, bytes.Length);
msx.Seek(0, 0);
string sx = (string)bfx.Deserialize(msx);

MessageBox.Show("Still intact :" + sx);

MessageBox.Show("Deserialize string Length(still intact): " 
    + sx.Length.ToString());

BinaryFormatter bfy = new BinaryFormatter();
MemoryStream msy = new MemoryStream();
bfy.Serialize(msy, sx);
msy.Seek(0, 0);
byte[] bytesy = msy.ToArray();

MessageBox.Show("Deserialize bytes Length(still intact): " 
   + bytesy.Length.ToString());

Answer 5

I'm not sure, but I think the string stores its info as an array of Chars, which is inefficient with bytes. Specifically, the definition of a Char is "Represents a Unicode character".

take this example sample:

String str = "asdf éß";
String str2 = "asdf gh";
EncodingInfo[] info =  Encoding.GetEncodings();
foreach (EncodingInfo enc in info)
{
    System.Console.WriteLine(enc.Name + " - " 
      + enc.GetEncoding().GetByteCount(str)
      + enc.GetEncoding().GetByteCount(str2));
}

Take note that the Unicode answer is 14 bytes in both instances, whereas the UTF-8 answer is only 9 bytes for the first, and only 7 for the second.

So if you just want the bytes used by the string, simply use Encoding.Unicode, but it will be inefficient with storage space.

Answer 6

You can use following code to convert a string to a byte array in .NET

string s_unicode = "abcéabc";
byte[] utf8Bytes = System.Text.Encoding.UTF8.GetBytes(s_unicode);