command line in C#

Question

I have a tool which I want to run from my command prompt.

The code is as

 static void Main(string[] args) { string User; if (args[0].Length != 0) { User = args[0]; } else { Console.Write("Please Enter the Username"); User = Console.ReadLine(); }

If I didnt give the username or the first argument after my 'tool.exe' in command prompt, it throws an exception like "Index was outside the bounds of the array"

I want ouptut as, if I didnt give argument - it should prompt me to give the username. please help me out.

J. Steen · Accepted Answer · 2012-09-18 10:48:59Z

args is an array, and is what you should be checking for length. When you check args[0].Length you're actually assuming there's atleast one element in the array already and thus you're checking Length of the first item.

Try

if (args.Length != 0)

instead, which checks the length of the array of command line parameters.

Daniel A. White · Accepted Answer · 2012-09-18 10:48:33Z

You don't want to call Length on the item.

 \/ Change here if (args.Length != 0) { User = args[0]; } else { Console.Write("Please Enter the Username"); User = Console.ReadLine(); }

Jordy van Eijk · Accepted Answer · 2012-09-18 10:49:27Z

1

You need to change the if to:

static void Main(string[] args) { string User; if (args.Length != 0) // Change from args[0] to args { User = args[0]; } else { Console.Write("Please Enter the Username"); User = Console.ReadLine(); } }

After this call make sure you do a string.IsNullOrEmpty(User) beforen you use it.

answered Sep 18, 2012 at 10:49

Jordy van Eijk

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3 Comments

J. Steen Over a year ago

Why the need to check for null or empty? Considering args.Length will only evaluate to larger than 0 if it's actually NOT null and NOT empty, what's the need for the extra check?

Jordy van Eijk Over a year ago

If it is then he does the Console.Readline(); thats why i say this.

J. Steen Over a year ago

Ah - after his Console.ReadLine(). Right. Wasn't entirely clear. =)

J. Steen · Accepted Answer · 2012-09-18 10:59:16Z

do this

static void Main(string[] args) { string User; if (args.Length > 0) { User = args[0]; } else { Console.Write("Please Enter the Username"); User = Console.ReadLine(); } }

Ran Avnon · Accepted Answer · 2012-09-18 10:54:37Z

Just replace the following line:

if (args[0].Length != 0)

With the following code:

if(arg.Length !=0) <br>

In your code, you have referenced item 0 in the args array and then check its length.
Since you want to check the array length, use the Length property of the array itselft

Tom · Accepted Answer · 2012-09-18 10:56:56Z

You have to check length of argument array, i.e. the number of arguments. Currently you are checking the size of args[0].

if (args.Length != 0) { // command have some params } else { // command have no params }

Jonas W · Accepted Answer · 2012-09-18 10:59:07Z

By doing like this you are looking on the first element in the collection string[].

if (args[0].Length != 0)

This will give a exception if there isn't any arguments. Correct statement are the following if you want to check if there is any arguments.

if (args.Length != 0) //Or this if (args.Any())

Observe that the Any() is a part of the namespace System.Linq.

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