CS1003 Syntax error, 'when' expected

Question

Its been quite some time that I read about Exception filters in C# 6.0

I was to trying to use it in action. But not sure why I am getting the below error.

CS1003 Syntax error, 'when' expected C_6.0

This is how my snippet looks like

using System;
using static System.Console;

namespace C_6._0
{
public class Program
{
    static void Main(string[] args)
    {
        int val = 1;
        try
        {
            WriteLine("Enter value :");
            val = int.Parse(ReadLine());

        }
        catch (Exception ex) if (val == 0)
        {
            WriteLine("Input Invalid");
        }
        catch (Exception ex)
        {
            WriteLine(ex.Message);
        }
        ReadLine();
    }
 }}

I checked the version of C#, its 6.0 in my visual studio by

Properties -> Build -> Advanced Build Settings

Thanks.

What happens if you change if (val == 0) to when (val == 0)? — mjwills
– mjwills, Commented Sep 22, 2017 at 12:32
@mjwills, it builds but the links that I was referring shows to use if — Kgn-web
– Kgn-web, Commented Sep 22, 2017 at 12:35
In early development of C# 6, it was if but they eventually changed it to when. — Dennis_E
– Dennis_E, Commented Sep 22, 2017 at 12:37
@Kgn-web it's better to read the docs than articles on various sites. — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Sep 22, 2017 at 12:37

Gilad Green · Accepted Answer · 2017-09-22 12:47:26Z

6

Many links online do show that the if should be correct but it is not true anymore. Syntax of the filtered exception is with when and not if:

try
{
    // Code here
}
catch (Exception ex) when (val == 0)
{
    WriteLine("Input Invalid");
}

See here on Official MSDN documentation

The article you commented is out of date. As mentioned by mjwills the reason is that in previous versions of the Visual Studio 2015 CTP, the if keyword was used instead of when.

edited Sep 22, 2017 at 12:47

answered Sep 22, 2017 at 12:32

Gilad Green

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3 Comments

Kgn-web Over a year ago

But all this links says about using if c-sharpcorner.com/UploadFile/7ca517/…

Kgn-web Over a year ago

Cool.. Thanks :)

Kgn-web Over a year ago

Also, it would be really great if you could please add just line to your post Note: In previous versions of the Visual Studio 2015 CTP, the if keyword was used instead of when.

mjwills · Accepted Answer · 2017-09-22 12:38:15Z

2

Exception filtering used to use if (in CTP) but now uses when.

catch (Exception ex) when (val == 0)

This blog entry states:

Note: In previous versions of the Visual Studio 2015 CTP, the if keyword was used instead of when.

answered Sep 22, 2017 at 12:38

mjwills

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Comments

Alejandro · Accepted Answer · 2017-09-22 13:22:46Z

0

Use when instead of if

catch (Exception ex) when (val == 0)

edited Sep 22, 2017 at 13:22

Alejandro

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answered Sep 22, 2017 at 12:32

Arsen Mkrtchyan

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