Why there isn’t any reference in the IEqualityComparer documentation to pre-implmented classes that override the function I don’t know.
But here’s one for string comparisons:
StringComparer
This static class contains many different predefined IEqualityComparer instances to be used in functions like “Contains”. Enjoy.
Here is the simple way to get all of the IP addresses for you machine. This code filters out everything but IPv4 address, but to truly get everything just remove the if statement.
string hostName = Dns.GetHostName();
var addrs = Dns.GetHostAddresses(hostName);
bool hasIP = false;
for (int i = 0; i < addrs.Length; i++)
{
IPAddress addr = addrs[i];
if (addr.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
{
si.DataIP = addr.ToString();
hasIP = true;
break;
}
}
Here’s the code to set the position of the caret in a richedit control
int position = 12; richedit1.Select( position, 0 ); richedit1.ScrollToCaret(); // if you want the position to be shown
It’s that simple.
I’ve often been frustrated by the sql that linq produces. Usually it’s really good, but occasionally it produced monstrosities. The hard part is getting at the sql that’s produced by a function. Hovering over the statement in the idea is a real pain so instead I created the following class that dumps the sql to a file
public class DCLogger : IDisposable
{
private StringWriter writer;
public DCLogger(System.Data.Linq.DataContext dc)
{
writer = new StringWriter();
dc.Log = writer;
}
#region IDisposable Members
public void Dispose()
{
writer.Flush();
System.IO.File.WriteAllText( "c:\\temp\\sql.log", writer.ToString() );
}
#endregion
}
To use it just create it passing it you data context. The results are written to the file when it’s disposed.
using( DCLogger( dc ) )
{
// ... some linq statement that executes
}
There are four different string comparisons for handling string fields with linq to sql. They are as follows:
The exact macth
DataContext dc = new DataContext(...) var results = from row in dc.table where row.string_column == "Exact Match" select row;
Begins With:
DataContext dc = new DataContext(...)
var results =
from row in dc.table
where row.string_column.StartsWith("Ex")
select row;
produces an sql match string “Ex%”
Contains
DataContext dc = new DataContext(...)
var results =
from row in dc.table
where row.string_column.Contains("Ex")
select row;
Which is equivalent to “%Ex%”
Ends With
DataContext dc = new DataContext(...)
var results =
from row in dc.table
where row.string_column.EndsWith("Ex")
select row;
Which is equivalent to “%Ex”
I’ve recently been writing an application that builds a linq to sql query dynamically. For instance:
MyDataContext dc() = new MyDataContext; var query = dc.MyTables; query = query.Where( t=>t.id > 10);
and so I want to order it by a certain column:
query = query.OrderBy( t=>t.id )
but the problem is the order direction isn’t know before hand so at first I was stuck with the following:
if ( descending )
query = query.OrderByDescending( t=>t.id);
else
query = query.OrderBy(t=>t.id);
Now if there is only a few possible columns to sort against it isn’t too bad. But when you have 10 different possible columns it really makes a lot of extra work just to control to sort direction. So I made a little helper class that allows the following. It works with linq and linq to sql:
query = query.OrderByAscDec( t=>t.id, descending );
here’s the static class that implments the OrderByAscDec function:
static class VPLinqExtensions
{
public static IOrderedQueryable<TSource> OrderByAscDes<TSource, TKey>(
this IQueryable<TSource> source,
System.Linq.Expressions.Expression<Func<TSource,
TKey>> keySelector, bool IsDescending)
{
if (IsDescending)
return source.OrderByDescending(keySelector);
else
return source.OrderBy(keySelector);
}
}
There doesn’t seem to be much written on blocking socket with c#. So I’ll write a very short piece, and I’ll only concentrate on client sockets.
Creating a socket is easy here is how:
using System.Net.Sockets; //... // Creating a connection Socket client; client = new Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp ); client.Connect(hostName, port); client.Blocking = false; // This needs to be done after Connect or it will error out.
Here’s how to write data to the socket
// Writing information to the socket
byte[] buffer = ASCIIEncoding.ASCII.GetBytes(messageText);
foreach (byte c in buffer)
{
SocketError err = SocketError.WouldBlock;
// need to try again if the socket would have blocked
while ( err == SocketError.WouldBlock )
{
// this version of Send must be used or an exception would be thrown, which I feel is a pain
// to deal with -- this way you can see handle the error appropriately.
client.Send(buffer, 0, 1, SocketFlags.None, out err );
}
if ( err != SocketError.Success )
{
// handle error
break;
}
}
And now code to read from a non-blocking socket
// Reading from the socket
// this loop keeps going until there is a socket error or a '0' byte is read which
// in this example marks the end of the message
System.Text.StringBuilder message = new System.Text.StringBuilder();
while ( true )
{
byte c = 0;
int bytesRead;
SocketError err;
// read a character.
bytesRead = client.Receive(buffer, 0, 1, SocketFlags.None, out err );
// checking what happened
if ( SocketError.Success == err )
{
// read a byte! Let's process it
if ( bytesRead > 0 )
{
// found a null character -- in this case it makes the end of a message.
if (c == 0)
{
// null terminated message received
break;
}
else
message.Append((char)c);
}
}
}
else if ( SocketError.WouldBlock != err )
{
break;
}
}
Reading the contents of a web page can be very useful. Here’s some code I’m developing to read the historical stock prices from http://finance.google.com
string uri = "http://finance.google.com/finance/historical?cid=667226&startdate=Sep+9%2C+2007&enddate=Sep+10%2C+2008&output=csv";
WebRequest request = WebRequest.Create(uri);
WebResponse response = request.GetResponse();
var stream = response.GetResponseStream();
StreamReader reader = new StreamReader(stream, Encoding.GetEncoding("utf-8"));
string page = reader.ReadToEnd();
There you go. Very simple isn’t it? Just got to love .Net
Here are some timing functions that come in the .Net framework. I’ve used these for moderately accurate timing code — at least down to the millisecond level. For any timing less than about 30 milliseconds these work much better than timer events piled on each other which tend to get inaccurate.
int begin = System.Environment.TickCount ... do something int end = System.Environment.TickCount int elapsed = end - begin;
Here’s how to get an array of file descriptors (name and other information).
System.IO.DirectoryInfo di = new System.IO.DirectoryInfo(Program.DataDirectory);
System.IO.FileInfo[] files = di.GetFiles("*.txt");