PV178: Programming for the CLI Environment
Seminar: Week 3
Michal Ordelt
Institute of Computer Science and Faculty of Informatics
Masaryk University
March 19, 2007
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public virtual string ToStringO
This method returns a human-readable string that represents the
current Object.
Example:
Modify L i b r a r y class and Book structure from previous seminar.
For displaying do not use P r i n t () method, override T o S t r i n g
method and use C o n s o l e . W r i t e O method. Do not forget to
display capacity. Use S t r i n g B u i l d e r class.
i using System . 10 ;
2 \ \ d e c l a r i n g a T e x t R e a d e r
3 p r i v a t e T e x t R e a d e r t e x t r e a d e r ;
4 \ \ a s i g n i n g a s t r e a m t o T e x t R e a d e r
5 t e x t r e a d e r = new S t r e a m R e a d e r ( path );
Example:
Create GetData:IEnumerable<string> class with constructor
having one parameter of type s t r i n g . The class reads lines from
the text file specified by the parameter and returns enumerator
that goes throught lines of file. Try your class on the file from IS.
A regular expression consists of two types of characters: literals
and metacharacters. A literal is a character you wish to match in
the target string. A metacharacter is a special symbol that acts as
a command to the regular expression parser. The parser is the
engine responsible for understanding the regular expression.
All the objects associated with regular expressions are in the Base
Class Library namespace System.Text .RegularExpressions.
The central class for regular expression support is Regex, which
represents an immutable, compiled regular expression. Although
instances of Regex can be created, the class also provides a
number of useful static methods.
i using System . Text. RegularExpressions;
2 private Regex rx;
3 rx = new Regex( expression );
4 i f ( r x . l s M a t c h ( t e x t ) ) {
5 \ \ D o something
 I
Example:
Extend the previous example as follows. The constructor have two
parameters, the first is the path, the second is the regular
expression, and it returns only string matching the expression.
Implement one parametric constructor using two parametric
constructor.
Regex.Replace Method
public string Replace (
string input,
string replacement
)
Example:
Extend the previous example again. The returned strings will have
all rude words replaced by -.
C # , like many object-oriented languages, handles errors and
abnormal conditions with exceptions. An exception is an object
that encapsulates information about an unusual program
occurrence.
It is important to distinguish between bugs, errors, and exceptions.
A bug is a programmer mistake that should be fixed before the
code is shipped. Exceptions are not a protection against bugs.
Although a bug might cause an exception to be thrown, you should
not rely on exceptions to handle your bugs. Rather, you should fix
the bug.
When your program encounters an exceptional circumstance, such
as running out of memory, it throws (or "raises") an exception.
When an exception is thrown, execution of the current function
halts and the stack is unwound until an appropriate exception
handler is found.
To signal an abnormal condition in a C # class, you throw an
exception. To do this, use the keyword throw. This code creates a
new instance of System.Exception and then throws it:
i E x c e p t i o n e x c e p t i o n ;
2 e x c e p t i o n = new E x c e p t i o n (" S o m e t h i n g ^ b a d ^ h a p p e n e d " )
3 throw e x c e p t i o n ;
In C # , an exception handler is called a catch block and is created
with the catch keyword.
i Encoding encoding = Encoding . GetEncoding (codepage)
2 encoding . Get Bytes ( s t r i n g )
3 encoding. G e t S t r i n g f byte [ ] )
public StreamWriter (
string path,
bool append,
Encoding encoding
)
Example:
Create a class that convert text file from one coding to another
and saves it as new file. Use exceptions to cover all possible
problems, that may occur.
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