C# Using Multiple Arguments

Question

This is from a newer C# guy,

I have been back and forth through different questions posed on here but I haven't found anything that answers directly to what I need to know.

I have a console application that I want to pass arguments to, through the command line. This is what I have so far and it's working for a single argument, now I got to add another but I can't seem to figure out where to start.

static void Main(string[] args)
{
    if (args == null || args.Length== 0)
    {
        Console.WriteLine("that's not it");
        help();
    }
    else
    {
        for (int i = 0; i < args.Length; i++)
        {
            backupfolder = args[i];
        }
        checks();
    }
}

If I take everything out of my else statement how can I set what the args are and assign? Will the below work ?

static void Main(string[] args)
{
    if (args == null || args.Length== 0)
    {
        Console.WriteLine("that's not it");
        help();
    }
    else
    {
        string backupfolder = args[0];
        string filetype = args[1];
        checks();
    }
}

you need to add null check for second argument, cuz its possible that second argument is not sent and is null — Agent_Orange
– Agent_Orange, Commented Mar 20, 2018 at 6:38
Well, you can't be sure if you actually received 2 arguments unless you check it first, right? If you don't have 2nd argument, i.e args[1], you will get an exception. *Edit: And that's a pretty good formatted question for a "newer C# guy", you have my upvote :) — uTeisT
– uTeisT, Commented Mar 20, 2018 at 6:38
Start with args.Length != 2 (in the first check) when there should be always two arguments, or args.Length >= 2 when there should be at least two arguments. — Julo
– Julo, Commented Mar 20, 2018 at 6:43

Zohar Peled · Accepted Answer · 2018-03-20 06:50:01Z

7

You need to check the length of the args array before attempting to retrieve values from it:

static void Main(string[] args)
{
    // There must be at least 2 command line arguments...
    if (args == null || args.Length < 2)
    {
        Console.WriteLine("that's not it");
        help();
    }
    else 
    {
        string backupfolder = args[0]; 
        string filetype = args[1];
        checks();
    }
}

Another option, if you want to allow passing only some of the expected arguments:

static void Main(string[] args)
{
    // There must be at least 1 command line arguments.
    if (args == null || args.Length < 1)
    {
        Console.WriteLine("that's not it");
        help();
    }
    else 
    {
        // You already know there is at least one argument here...
        string backupfolder = args[0]; 
        // Check if there is a second argument, 
        // provide a default value if it's missing
        string filetype = (args.Length > 1) ? args[1] : "" ;
        checks();
    }
}

edited Mar 20, 2018 at 6:50

answered Mar 20, 2018 at 6:44

Zohar Peled

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2 Comments

user3542866 Over a year ago

Thank you, the second option was going to be my next question, so you hit it on the mark. Thanks, everyone.

CompuChip Over a year ago

Although most hobby programmers feel a bit like cheating by using libraries, in this case I can really recommend the Command Line Parser package on NuGet: nuget.org/packages/commandlineparser. It allows you to have *NIX-like command lines: --backup myfolder -t filetype --file file1 --file file2 -f file3 and have them automatically parsed into a class.

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