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Creating New Strings in the .NET Framework

The .NET Framework allows strings to be created using simple assignment, and also overloads a class constructor to support string creation using a number of different parameters. The .NET Framework also provides several methods in the System.String class that create new string objects by combining several strings, arrays of strings, or objects.

The easiest way to create a new String object is simply to assign a string literal to a String object.

You can use overloads of the String class constructor to create strings from character arrays. You can also create a new string by duplicating a particular character a specified number of times.

The following table lists several useful methods that return new string objects.

Method name

Use

String.Format

Builds a formatted string from a set of input objects.

String.Concat

Builds strings from two or more strings.

String.Join

Builds a new string by combining an array of strings.

String.Insert

Builds a new string by inserting a string into the specified index of an existing string.

String.CopyTo

Copies specified characters in a string into a specified position in an array of characters.

You can use the String.Format method to create formatted strings and concatenate strings representing multiple objects. This method automatically converts any passed object into a string. For example, if your application must display an Int32 value and a DateTime value to the user, you can easily construct a string to represent these values using the Format method. For information about formatting conventions used with this method, see the section on composite formatting.

The following example uses the Format method to create a string that uses an integer variable.

int numberOfFleas = 12;
string miscInfo = String.Format("Your dog has {0} fleas. " +
                                "It is time to get a flea collar. " + 
                                "The current universal date is: {1:u}.", 
                                numberOfFleas, DateTime.Now);
Console.WriteLine(miscInfo);
// The example displays the following output: 
//       Your dog has 12 fleas. It is time to get a flea collar.  
//       The current universal date is: 2008-03-28 13:31:40Z.

In this example,DateTime.Now displays the current date and time in a manner specified by the culture associated with the current thread.

The String.Concat method can be used to easily create a new string object from two or more existing objects. It provides a language-independent way to concatenate strings. This method accepts any class that derives from System.Object. The following example creates a string from two existing string objects and a separating character.

string helloString1 = "Hello";
string helloString2 = "World!";
Console.WriteLine(String.Concat(helloString1, ' ', helloString2));
// The example displays the following output: 
//      Hello World!

The String.Join method creates a new string from an array of strings and a separator string. This method is useful if you want to concatenate multiple strings together, making a list perhaps separated by a comma.

The following example uses a space to bind a string array.

string[] words = {"Hello", "and", "welcome", "to", "my" , "world!"};
Console.WriteLine(String.Join(" ", words));
// The example displays the following output: 
//      Hello and welcome to my world!

The String.Insert method creates a new string by inserting a string into a specified position in another string. This method uses a zero-based index. The following example inserts a string into the fifth index position of MyString and creates a new string with this value.

string sentence = "Once a time.";   
 Console.WriteLine(sentence.Insert(4, " upon"));
 // The example displays the following output: 
 //      Once upon a time.

The String.CopyTo method copies portions of a string into an array of characters. You can specify both the beginning index of the string and the number of characters to be copied. This method takes the source index, an array of characters, the destination index, and the number of characters to copy. All indexes are zero-based.

The following example uses the CopyTo method to copy the characters of the word "Hello" from a string object to the first index position of an array of characters.

string greeting = "Hello World!";
char[] charArray = {'W','h','e','r','e'};
Console.WriteLine("The original character array: {0}", new string(charArray));
greeting.CopyTo(0, charArray,0 ,5);
Console.WriteLine("The new character array: {0}", new string(charArray));
// The example displays the following output: 
//       The original character array: Where 
//       The new character array: Hello
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