Question

I’m trying to convert the hexadecimal representation of a 64-bit number (e.g., the string "FFFFFFFFF") to binary representation ("11111...").

I’ve tried

string result = Convert.ToString(Convert.ToUInt64(value, 16), 2);

but this results in a confusing compiler error:

The best overloaded method match for ‘System.Convert.ToString(object, System.IFormatProvider)’ has some invalid arguments

Argument 2: cannot convert from ‘int’ to ‘System.IFormatProvider’

Answer 1

There might be a better solution, but check if this works:

public static string HexToBinary(string hexValue)
{
    ulong number = UInt64.Parse(hexValue, System.Globalization.NumberStyles.HexNumber);

    byte[] bytes = BitConverter.GetBytes(number);

    string binaryString = string.Empty;
    foreach (byte singleByte in bytes)
    {
        binaryString += Convert.ToString(singleByte, 2);
    }

    return binaryString;
}

The most convenient way would be to use Convert.ToString(Int64, Int32), but there is no overload for ulong. Another solution is Convert.ToString(UInt64, IFormatProvider) and write your own IFormatProvider. By looking at the examples I found an IFormatProvider that formats numbers in binary, octal and hex string representation: http://msdn.microsoft.com/en-us/library/system.icustomformatter.aspx.
The code there looks very similar to what I provided, so I thinks its not a bad solution.