C# 0 The Complete Reference

PART II

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Padding and Trimming Strings

Sometimes you will want to remove leading and trailing spaces from a string. This type of 

operation, called 

trimming,

 is often needed by command processors. For example, a database 

might recognize the word “print.” However, a user might enter this command with one or 

more leading or trailing spaces. Any such spaces must be removed before the string can be 

recognized by the database. Conversely, sometimes you will want to pad a string with 

spaces so that it meets some minimal length. For example, if you are preparing formatted 

output, you might need to ensure that each line is of a certain length in order to maintain 

alignment. Fortunately, C# includes methods that make these types of operations easy.

To trim a string, use one of these 

Trim( )

 methods:

public string Trim( )

public string Trim(params char[ ] 

chrs

)

The first form removes leading and trailing whitespace from the invoking string. The second 

form removes leading and trailing occurrences of the characters specified by 

chrs.

 In both 

cases, the resulting string is returned.

You can pad a string by adding characters to either the left or the right side of the string. 

To pad a string on the left, use one of the methods shown here:

public string PadLeft(int 

len

)

public string PadLeft(int 

len

, char 

ch

)

The first form adds spaces on the left as needed to the invoking string so that its total length 

equals

len.

 The second form adds the character specified by 

ch

 as needed to the invoking 

string so that its total length equals 

len.

 In both cases, the resulting string is returned. If 

len

 is 

less than the length of the invoking string, a copy of the invoking string is returned unaltered.

To pad a string to the right, use one of these methods:

public string PadRight(int 

len

)

public string PadRight(int 

len

, char 

ch

)

The first form adds spaces on the right as needed to the invoking string so that its total 

length equals 

len.

 The second form adds the characters specified by 

ch

 as needed to the 

invoking string so that its total length equals 

len.

 In both cases, the resulting string is returned. 

If

len

 is less than the length of the invoking string, a copy of the invoking string is returned 

unaltered.

The following program demonstrates trimming and padding:

// Trimming and padding.

using System;

class TrimPadDemo {

  static void Main() {

    string str = "test";

    Console.WriteLine("Original string: " + str);

    // Pad on left with spaces.

    str = str.PadLeft(10);

    Console.WriteLine("|" + str + "|");

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    // Pad on right with spaces.

    str = str.PadRight(20);

    Console.WriteLine("|" + str + "|");

    // Trim spaces.

    str = str.Trim();

    Console.WriteLine("|" + str + "|");

    // Pad on left with #s.

    str = str.PadLeft(10, '#');

    Console.WriteLine("|" + str + "|");

    // Pad on right with #s.

    str = str.PadRight(20, '#');

    Console.WriteLine("|" + str + "|");

    // Trim #s.

    str = str.Trim('#');

    Console.WriteLine("|" + str + "|");

  }

}

The output is shown here:

Original string: test

|      test|

|      test          |

|test|

|######test|

|######test##########|

|test|