Regex is not working in c# but working in javascript

Question

I am trying to validate string should not start with some character and should not contain <>.

[Required]
[Display(Name = "First name")]
[MaxLength(50)]
[RegularExpression(@"(?=(^(?!.*[><]).*$))(?=(^(?![@\+\-=\*]).*))", ErrorMessage = "firstname"+ Constants.DisplayMessage)]
public string firstname { get; set; }

this regex is working in javascript. but it is not working in c#. I have already spent almost 1 hours on it but no result please help me. ya also tried using (^(?!.*[><]).*$)|(^(?![@\+\-=\*]).*) this regex.but it is not working. I am not good at regex so please help me.

What is this regex for? What do you expect from $ in the middle of expression? — Alex Seleznyov
– Alex Seleznyov, Commented Jan 19, 2018 at 6:10
Please give some background for what this regex is supposed to be doing. It may even be that you could use a simpler pattern in both places. — Tim Biegeleisen
– Tim Biegeleisen, Commented Jan 19, 2018 at 6:11
@AlexSeleznyov you can use regexr.com it will help you to understand what I am trying to do. — praval
– praval, Commented Jan 19, 2018 at 6:12
@TimBiegeleisen cannot contain < or > and cannot start with @, -, =, * characters — praval
– praval, Commented Jan 19, 2018 at 6:12
stackoverflow.com/questions/48295781/… Please check this answer once, it may help. — JyothiJ
– JyothiJ, Commented Jan 19, 2018 at 6:38

Tim Biegeleisen · Accepted Answer · 2018-01-19 06:29:35Z

2

Based on your description what the regex needs to do, the following pattern should work:

^(?![@=*-])(?!.*[<>]).*$

Explanation:

^
(?![@=*-])    from the start of string, assert that @=*- is not the first character
(?!.*[<>])    also assert that <> does not appear anywhere in the string
.*            then match anything (our assertions having be proven true)
$

Demo

This pattern is also working for C#, as you can see by exploring the second demo below.

C# Demo

edited Jan 19, 2018 at 6:29

answered Jan 19, 2018 at 6:15

Tim Biegeleisen

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6 Comments

praval Over a year ago

thank you, I am testing it on my c# code give me 5 min.

praval Over a year ago

it is working on javascript but not working on c#. and you are testing it on javascript regex engine.

praval Over a year ago

in c# I am using RegularExpression Attribute.

Tim Biegeleisen Over a year ago

@pravaljain The pattern seems to work fine for me in C#. Have a look at the demo I added to my answer. My guess is that you are using one of their APIs incorrectly.

praval Over a year ago

thanks, Tim but for your demo, I replaced your regex with mine and my is also working but I don't know why it is not working on the attribute. I think I am using API incorrectly.

|

JyothiJ · Accepted Answer · 2018-01-19 07:07:17Z

0

Having proper set validator, it works in C# too public class NameProp { string m_firstname;

    [Required]
    [Display(Name = "First name")]
    [MaxLength(50)]
    [RegularExpression(@"^(?![@=*-])(?!.*[<>]).*$", ErrorMessage = "firstname contains <> or start with @=*-")]
    public string firstname
    {
        get { return m_firstname; }

        set
        {
            Validator.ValidateProperty(value,
                new ValidationContext(this, null, null) { MemberName = "firstname" });
            m_firstname = value;
        }
    }

}

public class Program {

    static void Main(string[] args)
    {
        NameProp np = new NameProp();
        try
        {
            np.firstname = "<>JJ";
        }
        catch (ValidationException ex)
        {
            Console.WriteLine(ex.Message);
        }

    }
}

answered Jan 19, 2018 at 7:07

JyothiJ

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1 Comment

JyothiJ Over a year ago

Also please refer codeproject.com/Tips/550784/Validation-using-DataAnnotations for more details

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