How to use variable inside String.Format

Question

I want to use String.Format inside the loop, but it does not allowing me to define a variable i inside the String.Format. Here is my code

StringBuilder Sb;
for(i=0 ;i<=myObj.length;i++)
{
    Sb=Sb.Append(String.Format("{i,5}",myObj[i].Tostring()));
}

What is that supposed to show? Are you trying to print i followed by myObj[i]? — itsme86
– itsme86, Commented Sep 16, 2016 at 17:24
i am trying to generate a fixed width file. i is the index or columns of the array object — TRA
– TRA, Commented Sep 16, 2016 at 17:42

Joe Enos · Accepted Answer · 2016-09-16 17:51:35Z

4

To use it in the Format method, you use numbers corresponding to the indexes of the params array.

Also, don't reassign Sb, just call Append or AppendFormat:

Sb.Append(String.Format("{0,5}", myObj[i].ToString()));
//or
Sb.AppendFormat("{0,5}", myObj[i].ToString());

If you're fortunate enough to be on the latest and greatest C# version, you can skip Format and do it with the new string interpolation syntax:

Sp.Append($"{myObj[i],5}");

Or since all you're doing is padding, then you can also do:

Sb.Append(myObj[i].ToString().PadLeft(5));

edited Sep 16, 2016 at 17:51

answered Sep 16, 2016 at 17:28

Joe Enos

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3 Comments

Luiso Over a year ago

There is no need to call ToString() on myObj[i] as it is called by default

Joe Enos Over a year ago

@Luiso Technically calling ToString() on a value type (if the parameters are value types) will prevent the boxing that would occur prior to ToStringing the value, and could potentially affect performance slightly (negligible, but still technically not equivalent). I agree though, that personally I would remove ToString().

TRA Over a year ago

The problem using PadLeft/PadRight is that , the last coulmn i need to fill with a blank space of 100 and it is not taking the 100 spaces ,wheres as just taking 8 spaces .

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