Remove characters in string when it reaches specific length

Question

In my application I am allowing string length upto 255 characters while entering in Database.

What I need is I have a field called "Name", I am entering the value like

Name = DisplayName + "_" + UniqueName;

And I am checking the whole "Name" value is greater than 255 and if so, Need to remove that extra characters from DisplayName alone.

Something like, Name = "abcefghijklmnopqrstuvwxyz" + "_" + "zyxwvutsrqponmlkjihgfecba";

If I have string like this and if the char greater than 255, (say 270) I need to remove 15 char from display name.

How to achieve this in C# ??

Answer 1

The question is a little unclear to me. But if you want to remove the extra characters from Name after setting its value you could use String.Substring

Name = DisplayName + "_" + UniqueName;
Name = Name.Length()<=255 ? Name : Name.SubString(0,254);

Answer 2

Assuming DisplayName and UniqueName are assured to not contain your delimiter character "_", you will have to split the string, modify (what used to be) DisplayName and reconcat them:

var displayName = "Shesha";
var uniqueName = "555";
var fullName = displayName + "_" + uniqueName;

if (fullName.Length > 255)
{
   var charsToRemove = fullName.Length - 255;

   // split on underscore.
   var nameParts = fullName.Split('_'); 

   var displayNameLength = nameParts[0].Length;
   var truncatedDisplayName = nameParts[0].Substring(0, displayNameLength - charsToRemove);
   fullName = truncatedDisplayName + "_" + nameParts[1];
}

Of course, all this assumes that this length check occurs after the full name has been constructed. You can of course do the check before, saving yourself the effort of splitting:

var combinedLength = displayName.Length + uniqueName.Length + 1; // 1 for _.
var charsToRemove = combinedLength - 255;
if (charsToRemove > 0)
{
    // same logic as above, but instead of splitting the string, you have
    // the original parts already.
}

And of course, this is just a basic example. Real code should also have:

1. Variables/constants/configuration to specify the maximum length and maybe the delimiter character as well.
2. Error checking to make sure Split() returns exactly two parts, for instance.

Answer 3

I made an extension method to do this:

public static string RemoveExcessCharacters(this string value, int maxLen)
{
   return (value.Length > maxLen) ? value.Substring(0, maxLen) : value;
}

Used like:

string value = "abcdefg".RemoveExcessCharacters(3);

Returns "abc"