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Hex to Decimal in C#

Two alternate ways of converting a hex string to decimal

Summary

The other day I needed to write some code to convert an integer expressed in hexadecimal to decimal. I was surprised to find that the way to do it wasn’t the way I expected.

The value I was processing had come from a different environment and had a ‘0x’ prefix to define its base – it was also a string. I just assumed i could feed this to int.Parse and I’d get the answer I was after.

In fact it seems that you either have to get rid of the ‘0x’ prefix or find some other way of doing it. I write a little program to illustrate the choices.

AllowHexSpecifier Weirdness

One thing to notice here which is really quite strange is that the int.Parse option takes an enumerated type argument System.Globalization.NumberStyles.AllowHexSpecifier when in fact it doesn’t allow a Hex specifier ! I’m sure there’s some sense to that but I don’t see it myself !

Example Code

using System;
using System.Collections.Generic;
using System.Text;
using System.Globalization;

namespace HexParsing
{
    class Program
    {
        static void Main()
        {
            string strTestHex ;
            int iTestHex;
            string sOut;
            string s1 = "{0} converted to base 10 using int.Parse is {1}";
            string s2 = "{0} converted to base 10 using Convert.ToInt32 is {1}";

            //Without a prefix - using int.Parse
            strTestHex = "7FC3DAE0";
            iTestHex = int.Parse(   strTestHex,
                                    System.Globalization.NumberStyles.AllowHexSpecifier,
                                    CultureInfo.CurrentCulture);
            sOut = String.Format(CultureInfo.CurrentCulture, s1, strTestHex, iTestHex);
            Console.WriteLine(sOut);

            //With a prefix - using Convert.ToInt32
            strTestHex = "0x7FC3DAE0";
            iTestHex = Convert.ToInt32(strTestHex,16);
            sOut = String.Format(CultureInfo.CurrentCulture, s2, strTestHex, iTestHex);
            Console.WriteLine(sOut);

            Console.WriteLine("Press ENTER to close window");
            Console.ReadLine();

        }
    }
}