asp.net barcode Getting a Range of Characters in Visual C#.NET

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Getting a Range of Characters
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You can obtain a contiguous range of characters within a string by using the Substring method. There are a couple of overloads of this method, and Example 10-52 shows them in action.
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string myString = "This is the silliest stuff that ere I heard."; string subString = myString.Substring(5); string anotherSubString = myString.Substring(12, 8); Console.WriteLine(subString); Console.WriteLine(anotherSubString);
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Notice that both of these overloads return a new string, containing the relevant portion of the original string. The first overload starts with the character at the specified index, and returns the rest of the string (regardless of how long it might be). The second starts at the specified index, and returns as many characters as are requested. A very common requirement is to get the last few characters from a string. Many platforms have this as a built-in function, or feature of their strings, but the .NET Framework leaves you to do it yourself. To do so depends on us knowing how many characters there are in the string, subtracting the offset from the end, and using that as our starting index, as Example 10-53 shows.
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static string Right(string s, int length) { int startIndex = s.Length - length; return s.Substring(startIndex); }
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Notice how we re using the Length property on the string to determine the total number of characters in the string, and then returning the substring from that offset (to the end). We could then use this method to take the last six characters of our string, as Example 10-54 does.
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string myString = "This is the silliest stuff that ere I heard."; string subString = Right(myString, 6); Console.WriteLine(subString);
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If you build and run this sample, you ll see the following output:
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heard.
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Extension Methods for String
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You will probably build up an armory of useful methods for dealing with strings. It can be helpful to aggregate them together into a set of extension methods. Here s an example implementing the Right method that we ve used as an example in this chapter, but modifying it to work as an extension method, and also providing an equivalent to the version of Substring that takes both a start position and a length:
public static class StringExtensions { public static string Right(this string s, int length) { int startIndex = s.Length - length; return s.Substring(startIndex); } public static string Right(this string s, int offset, int length) { int startIndex = s.Length - offset; return s.Substring(startIndex, length); } }
By implementing them as extension methods, we can now write code like this:
string myString = "This is the silliest stuff that ere I heard."; string subString = myString.Right(6); string subString2 = myString.Right(6, 5); Console.WriteLine(subString); Console.WriteLine(subString2);
This will produce output like the following:
heard. heard
Notice that the Length of the string is the total number of characters in the string much as the length of an array is the total number of entities in the array, not the number of bytes allocated to it (for example).
Composing Strings
You can create a new string by composing one or more other strings. Example 10-55 shows one way to do this.
string fragment1 = "To be, "; string fragment2 = "or not to be."; string composedString = fragment1 + fragment2; Console.WriteLine(composedString);
Here, we ve used the + operator to concatenate two strings. The C# compiler turns this into a call to the String class s static method Concat, so Example 10-56 shows the equivalent code.
string composedString2 = String.Concat(fragment1, fragment2); Console.WriteLine(composedString2);
Don t forget we re taking the first two strings, and then creating a new string that is fragment1.Length + fragment2.Length characters long. The original strings remain unchanged.
There are several overloads of Concat, all taking various numbers of strings this enables you to concatenate multiple strings in a single step without producing intermediate strings. One of the overloads, used in Example 10-57, can concatenate an entire array of strings.
static void Main(string[] args) { string[] strings = Soliloquize(); string output = String.Concat(strings); Console.WriteLine(output); Console.ReadKey(); } private static string[] Soliloquize() { return new string[] { "To be, or not to be--that is the question:", "Whether 'tis nobler in the mind to suffer", "The slings and arrows of outrageous fortune", "Or to take arms against a sea of troubles", "And by opposing end them." }; }
If we build and run that example, we ll see some output like this:
To be, or not to be--that is the question:Whether 'tis nobler in the mind to suf ferThe slings and arrows of outrageous fortuneOr to take arms against a sea of t roublesAnd by opposing end them.
That s probably not quite what we meant. We ve been provided with each line of Hamlet s soliloquy, and we really want the single output string to have breaks after each line. Instead of using String.Concat, we can instead use String.Join to concatenate all of the strings as shown in Example 10-58. This lets us insert the string of our choice between each string.
static void Main(string[] args) { string[] strings = Soliloquize(); string output = String.Join(Environment.NewLine, strings); Console.WriteLine(output); Console.ReadKey(); }
Here we re using the Environment.NewLine constant to get the line-break string appropriate for our platform (rather than explicitly using "\n" or "\r" or "\r\n").
For historical reasons, not all operating systems use the same sequence of characters to represent the end of a line. Windows (like DOS before it) mimics old-fashioned printers, where you had to send two control characters: a carriage return (ASCII value 13, or \r in a string or character literal) would cause the print head to move back to the beginning of the line, and then a line feed (ASCII 10, or \n) would advance the paper up by one line. This meant you could send a text file directly to a printer without modification and it would print correctly, but it produced the slightly clumsy situation of requiring two characters to denote the end of a line. Unix conventionally uses just a single line feed to mark the end of a line. Environment.NewLine is offered so that you don t have to assume that you re running on a particular platform. That being said, Console is flexible, and treats either convention as a line end. But this can matter if you re saving files to disk.
If we build and run, we ll see the following output:
To be, or not to be--that is the question: Whether 'tis nobler in the mind to suffer The slings and arrows of outrageous fortune Or to take arms against a sea of troubles And by opposing end them.
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