CE's Blog

Converting a byte array into a hexadecimal string is straight forward to do using a loop and a few lines of code. With Linq, it can be done more elegantly in a single line:

string s = String.Join( String.Empty, byte_array.Select( x => x.ToString( "X2" ) ).ToArray() );

Another one-liner without using Linq (also works on the framework 2.0):

string s = String.Join( String.Empty, Array.ConvertAll<byte, string>( byte_array, delegate( byte b ) { return b.ToString( "X2" ); } ) );

There is no Array.ConvertAll<>() in the .NET Compact Framework 2.0 however. But with a little help from the BitConverter class, a one-liner is still possible:

string s = BitConverter.ToString( byte_array ).Replace( "-", String.Empty );

Which one of the above is the most efficient? Most likely it does not matter, unless you are converting megabytes of data at once. Obviously, using Linq is the slowest option, it takes more than twice as long as Array.ConvertAll<>().
Using BitConverter.ToString() is the most efficient option, being about 8 times (!) as fast as Linq.

Finally, if you are interested in rolling your own function, here is a really fast one which can compete with the BitConverter class:

static readonly char[] hex = "0123456789ABCDEF".ToCharArray();
 
static string ByteToHexString( byte[] array )
{
    if ( array == null || array.Length < 1 )
        return String.Empty;
    char[] c = new char[ array.Length << 1 ];
    for ( int i = 0; i < array.Length; ++i )
    {
        byte b = array[ i ];
        c[ i << 1 ] = hex[ b >> 4 ];
        c[ ( i << 1 ) | 0x01 ] = hex[ ( b & 0x0F ) ];
    }
    return new string( c );
}