CODEWITHSUNDEEP
c#regexhex
apomene
apomene

Reputation: 14389

Check if string is valid representation of hex number

I am total noob regarding regex.

My goal is to check whether a string is a valid representation of a hex number.

Currently my implementation (which I find really inefficient) is having a List with all hex digits (0-9, A-F) and checking whether my string contains characters not contained in given List.

I bet this can be easily done using regular expressions but I have no idea how to implement it.

private bool ISValidHEX(string s)
{
    List<string> ToCheck = new List<string>();
    for (int i = 0; i < 10; i++)
    {
        ToCheck.Add(i.ToString());
    }
    ToCheck.Add("A");
    ToCheck.Add("B");
    ToCheck.Add("C");
    ToCheck.Add("D");
    ToCheck.Add("E");
    ToCheck.Add("F");
    for (int i = 0; i < s.Length; i++)
    {
        if( !ToCheck.Contains(s.Substring(i,1)))
        {
            return false;
        }
    }
    return true;
}

Upvotes: 11

Views: 22993

Answers (6)

ErrCode
ErrCode

Reputation: 306

If your hex string will have a maximum of 32 characters (e.g. usually GUIDs fit this bill), then you could PadLeft the string with zeros to ensure it has always 32 characters and then use the Guid.TryParse

public static bool IsHex(string hexString)
{
    var isHex = false;
    if ((hexString ?? string.Empty).Length == 0)
        return false;
    if (hexString.Length > 0 && hexString.Length <= 32)
    {
        hexString = hexString.PadLeft(32, '0');
        Guid guid;
        isHex = Guid.TryParse(hexString, out guid);
    }
    else
    {
        throw new NotImplementedException("Use some other way to check the hex string!");
    }
    return isHex;
}

Try it here: https://dotnetfiddle.net/bLaCAT

Upvotes: 0

Mashton
Mashton

Reputation: 6415

^[0-9a-fA-F]+$ will match strings which are numbers and valid hex letters BUT this doesn't match the possible 0x at the front. I'm sure you can add that if needed.

Upvotes: 2

Steve
Steve

Reputation: 216293

I recommend to use Int32.TryParse. There is an overload that allow the Hex numbers conversion

int v;
string test = "FF";
if(Int32.TryParse(test, NumberStyles.HexNumber, CultureInfo.CurrentCulture, out v))
   Console.WriteLine("Is HEX:" + v.ToString());

This is better than a simple Int32.Parse because, in the case that you have an invalid hex or the conversion overflows the Int32.MaxValue you don't get an exception but you could simply test the boolean return value.

Warning, the string cannot be prefixed with "0x" or "&H"

Upvotes: 4

Bathsheba
Bathsheba

Reputation: 234695

I would have thought that it's quickest to attempt to convert your string to an integral type and deal with any exception. Use code like this:

int num = Int32.Parse(s, System.Globalization.NumberStyles.HexNumber);

The resulting code is possibly easier to follow than a regular expression and is particularly useful if you need the parsed value (else you could use Int32.TryParse which is adequately documented in other answers).

(One of my favourite quotations is by Jamie Zawinski: "Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems.")

Upvotes: 25

Mike Meinz
Mike Meinz

Reputation: 506

I tried Google search. I found lots of solutions. Here are two:

Validate Hex Color Code with Regular Expression

Regular Expression Hexadecimal Number Validation

Example

//use System.Text.RegularExpressions before using this function
public bool vldRegex(string strInput)
{
//create Regular Expression Match pattern object
Regex myRegex = new Regex("^[a-fA-F0-9]+$");
//boolean variable to hold the status
bool isValid = false;
if (string.IsNullOrEmpty(strInput))
{
   isValid = false;
}
else
{
   isValid = myRegex.IsMatch(strInput);
}
//return the results
return isValid;
}

Upvotes: 2

Tigran
Tigran

Reputation: 62246

To simply check

Check if string is valid represantion of HEX number

you may use a method like: 

int res = 0; 
if(int.TryParse(val, 
         System.Globalization.NumberStyles.HexNumber, 
         System.Globalization.CultureInfo.InvariantCulture, out res)) {

      //IT'S A VALID HEX
}

Pay attention on System.Globalization.CultureInfo.InvariantCulture parameter, change it according to your needs.

Upvotes: 16

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