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Objectives
- Discuss string handling
– System.String class – System.Text.StringBuilder class
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String Objectives Discuss string handling System.String class - - PDF document
String Objectives Discuss string handling System.String class - - PDF document
String Objectives Discuss string handling System.String class System.Text.StringBuilder class 2 String class Framework Class Library provides System.String class represents immutable sequence of characters namespace
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String class
- Framework Class Library provides System.String class
– represents immutable sequence of characters
namespace System { public sealed class String ... { ... } }
String class
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String alias
- C# provides string as convenient alias for System.String
string s; System.String t;
equivalent
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String creation
- String is a reference type
– created with new – constructors available for char and char[]
char[] t = new char[5] { 'h', 'e', 'l', 'l', 'o' }; string a = new string(t); string b = new string(t, 0, 2); string c = new string('z', 3); entire array first 2 characters given character repeated 3 times
a hello b he c zzz
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String literals
- String literals automatically converted into string objects
– convenient shorthand for common case
string s = "hello";
string object created
s hello
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Escape sequence
- Can include escape sequence in string
– precede special characters with \
string a = "hello\n"; string b = "\""; string c = "C:\\WINDOWS"; ...
linefeed double quote backslash
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Verbatim string literal
- Can create verbatim string literal
– precede with @ – helps reduce need for escape sequences
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string path = @"C:\WINDOWS\Config";
verbatim
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String length
- String provides read only Length property
string s = "hello"; int l = s.Length;
length will be 5
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String indexer
- String provides read only indexer
– indices start at zero
string s = "hello"; char c = s[4];
retrieve 'o'
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String comparison
- String provides several ways to perform comparison
– all have value semantics
string a = "bike"; string b = "bit"; if (a.CompareTo(b) < 0) ... if (a.Equals(b)) ... if (a == b) ... if (a != b) ...
three way comparison, used for ordering equality equality inequality
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String concatenation
- String concatenation supported
– operator + – operator +=
string a = "holly"; string b = "wood"; string c = a + b;
- perator +
string d = "tom"; d += "cat";
- perator +=
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String immutability
- Strings are immutable
– no way to modify contents
- Operations which seem to modify string do not
– actually create new object to represent new value
string d = "tom"; d += "cat";
create new object, assign to reference
tom d tomcat
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String inefficiency
- Strings can be inefficient when used for concatenation
– may create and destroy many intermediate objects
string text = ""; for (int i = 0; i < 10; i++) { text += Console.ReadLine(); }
may create new
- bject each iteration
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StringBuilder class
- Framework Class Library provides StringBuilder class
– in System.Text namespace – represents mutable sequence of characters
namespace System.Text { public sealed class StringBuilder { ... } }
StringBuilder class
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StringBuilder mutability
- StringBuilder provides mutator methods
– change contents of existing object – can be more efficient than string for concatenation
StringBuilder text = new StringBuilder(); text.Append("<body>hello<html>"); text.Remove(12, 4); text.Insert(12, "/bode"); text[16] = 'y';
modify
text <body>hello</body>
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StringBuilder internally managed capacity
- StringBuilder adjusts capacity to accommodate contents
– no need for user interaction
StringBuilder text = new StringBuilder(); text.Append("<html>"); text.Append("<body>"); text.Append("<p>"); text.Append("hello"); ... text.Append("</p>"); text.Append("</body>"); text.Append("</html>");
capacity increased as needed
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StringBuilder user managed capacity
- StringBuilder allows user some control over capacity
– initial capacity during construction – read/write Capacity property
- Explicit management of capacity can be efficient
– if final length of string is known ahead of time
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StringBuilder a = new StringBuilder(100); a.Capacity = 200;
capacity of 100 capacity of 200
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StringBuilder typical usage
- StringBuilder typically used to create desired sequence
– result is then converted to string using ToString
string Create() { StringBuilder text = new StringBuilder(); text.Append("<html>"); text.Append("<body>"); text.Append("<p>"); text.Append("hello"); ... return text.ToString(); }
create convert
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Summary
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- .NET Framework Class Library has two string classes
– String – StringBuilder
- String is primary class
– offers most services – is most convenient to use
- StringBuilder is more specialized
– targeted toward creating string from pieces