Using an array as argument for string.Format()

Question

When trying to use an array as an argument for the string.Format() method, I get the following error:

FormatException: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.

The code is as follows:

place = new int[] { 1, 2, 3, 4};
infoText.text = string.Format("Player1: {0} \n Player2: {1} \n Player3: {2} \n Player4: {3}", place);

The Array contains four values and the arguments in the String.Format() are also the same.

What causes this error?

(The infoText.text is just a regular String object)

Perhaps something like string.Format("Player1: {0} \n Player2: {1} \n Player3: {2} \n Player4: {3}", place[0], place[1], place[2], place[3]); It works as you pass an object relating every {} in string — Awais
– Awais, Commented Nov 30, 2016 at 10:01
Just for the record, instead of using string.format, you could create the string more dynamically without hardcoding the number of players, e.g.: infoText.text = string.Join("\n", place.Select((p,i) => $"Player{i+1}: {p}")); — Me.Name
– Me.Name, Commented Nov 30, 2016 at 10:07

Balagurunathan Marimuthu · Accepted Answer · 2020-05-07 07:26:18Z

28

You can convert int array to string array as pass it using System.Linq Select() extension method.

infoText.text = string.Format("Player1: {0} \nPlayer2: {1} \nPlayer3: {2} \nPlayer4: {3}", 
                              place.Select(x => x.ToString()).ToArray());

Edit:

In C# 6 and above, you can also able to use String Interpolation instead of using string.Format()

infoText.text = $"Player1: {place[0]}\nPlayer2: {place[1]} \nPlayer3: {place[2]} \nPlayer4: {place[3]}";

Check this fiddle for your reference.

edited May 7, 2020 at 7:26

answered Nov 30, 2016 at 10:04

Balagurunathan Marimuthu

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2 Comments

martin36 Over a year ago

So the argument can be a string[] array but not an int[] array?

Balagurunathan Marimuthu Over a year ago

@martin36 not only string[] - your array should be an object or string type.

Tim Schmelter · Accepted Answer · 2016-11-30 10:07:58Z

11

Quick fix.

var place = new object[] { 1, 2, 3, 4 };

C# does not support co-variant array conversion from int[] to object[] therefor whole array is considered as object, hence this overload with a single parameter is called.

edited Nov 30, 2016 at 10:07

Tim Schmelter

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answered Nov 30, 2016 at 10:01

M.kazem Akhgary

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2 Comments

Joey Over a year ago

C# does support co-variant array conversion (e.g. from string[] to object[]), but in this case the conversion would also involve boxing of value types which is why it won't work.

Tim Schmelter Over a year ago

@Joey: he wrote "does not support co-variant array conversion from int[] to object[]" ;-)

Joey · Accepted Answer · 2016-11-30 10:10:00Z

6

It is possible to pass an explicit array for a params argument, but it has to have the matching type. string.Format has a few overloads, of which the following two are interesting to us:

string.Format(string, params object[])
string.Format(string, object)

In your case treating the int[] as object is the only conversion that works, since an int[] cannot be implicitly (or explicitly) converted to object[], so string.Format sees four placeholders, but only a single argument. You'd have to declare your array of the correct type

var place = new object[] {1,2,3,4};

edited Nov 30, 2016 at 10:10

answered Nov 30, 2016 at 10:01

Joey

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2 Comments

martin36 Over a year ago

What is the difference between params object[] and just a regular object[] array?

Joey Over a year ago

@martin36: You can treat the params parameter as any number of arguments. The compiler will automatically wrap them in an array to call the method.

Matías Fidemraizer · Accepted Answer · 2016-11-30 10:20:11Z

3

As others have already said, you can't convert int[] to object[]. But you can fix this issue using Enumerable.Cast<T>():

infoText.text = string.Format
(
      "Player1: {0} \n Player2: {1} \n Player3: {2} \n Player4: {3}",                        
      place.Cast<object>().ToArray()
);

BTW, if you're on C# 6 or above, you might consider using interpolated strings instead of string.Format:

infoText.text = $"Player1: {place[0]}\n Player 2: {place[1]} \n Player 3: {place[2]} \n Player 4: {place[3]}";

answered Nov 30, 2016 at 10:20

Matías Fidemraizer

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3 Comments

martin36 Over a year ago

I am using Unity and it has only the version C# 2.

martin36 Over a year ago

Oh sorry, but thanks for the answer anyways. I will remember it for later use.

Matías Fidemraizer Over a year ago

@martin36 No problem, it might be an useful suggestion for other readers too :)

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