C# work with local IP address

/// 
/// Ref: How To Get IP Address Of A Machine
/// Ref: WMI or How to change my IP address
/// using System.Management;
///

public string getLocalIP() 
{
  string localIP = "";
  string strHostName = Dns.GetHostName();

  IPHostEntry ipEntry = Dns.GetHostByName (strHostName);
  IPAddress [] addr = ipEntry.AddressList;

  /* what if more than one instance exists? */
  for (int i = 0; i < addr.Length; i++)  
  {
    localIP = addr[i].ToString();
  }

  return localIP;
}


public bool setLocalIP(string newIP) {
  try 
  {
    ManagementBaseObject inPar = null;
    ManagementBaseObject outPar = null;
    ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
    ManagementObjectCollection moc = mc.GetInstances();
    foreach (ManagementObject mo in moc) 
    {
      if (!(bool) mo["IPEnabled"]) continue;
      inPar = mo.GetMethodParameters("EnableStatic");
      inPar["IPAddress"] = new string[] {newIP};
      inPar["SubnetMask"] = new string[] {subnetMask};
      outPar = mo.InvokeMethod("EnableStatic", inPar, null);
      break;
    }
  
    this.currentIP = newIP;
    return true;
  } 
  catch (Exception e) 
  {
    this.setErrMsg(e.Message + "\nsource: " + e.Source);
    return false;
  }
}


static void SwitchToDHCP()
{
  ManagementBaseObject inPar = null;
  ManagementBaseObject outPar = null;
  ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
  ManagementObjectCollection moc = mc.GetInstances();
  foreach( ManagementObject mo in moc )
  {
    if( ! (bool) mo["IPEnabled"] )
      continue;

    inPar = mo.GetMethodParameters("EnableDHCP");
    outPar = mo.InvokeMethod( "EnableDHCP", inPar, null );
    break;
  }
}


static void SwitchToStatic()
{
  string newIP;
  string subnetMask = "255.255.255.0";
  newIP = (curIP.Equals("192.168.168.209"))?"192.168.168.204":"192.168.168.209";

  ManagementBaseObject inPar = null;
  ManagementBaseObject outPar = null;
  ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
  ManagementObjectCollection moc = mc.GetInstances();
  foreach( ManagementObject mo in moc )
  {
    if( ! (bool) mo[ "IPEnabled" ] )
      continue;

    inPar = mo.GetMethodParameters( "EnableStatic" );
    inPar["IPAddress"] = new string[] { newIP };
    inPar["SubnetMask"] = new string[] { subnetMask };
    outPar = mo.InvokeMethod( "EnableStatic", inPar, null );
    break;
  }
}


static void ReportIP()
{
  Console.WriteLine( "****** Current IP addresses:" );
  ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
  ManagementObjectCollection moc = mc.GetInstances();
  foreach( ManagementObject mo in moc )
  {
    if( ! (bool) mo[ "IPEnabled" ] )
      continue;

    Console.WriteLine( "{0}\n SVC: '{1}' MAC: [{2}]", (string) mo["Caption"],
      (string) mo["ServiceName"], (string) mo["MACAddress"] );

    string[] addresses = (string[]) mo[ "IPAddress" ];
    string[] subnets = (string[]) mo[ "IPSubnet" ];

    Console.WriteLine( " Addresses :" );
    foreach(string sad in addresses)
      Console.WriteLine( "\t'{0}'", sad );

    Console.WriteLine( " Subnets :" );
    foreach(string sub in subnets )
      Console.WriteLine( "\t'{0}'", sub );

    curIP = addresses[0];
  }
}

C# GET/POST request, login, download, axWebBrowser

///
/// Example of HTTP Get request.
///
private string requestURL(string url, int timeout) 
{
  HttpWebRequest wr;
  HttpWebResponse resp = null;
  Stream stream;
  StreamReader reader;
  string strResponse = "";

  try {
    wr = (HttpWebRequest) WebRequest.Create(url);
    wr.Timeout = timeout; // in milliseconds.
    resp = (HttpWebResponse) wr.GetResponse();
    stream = resp.GetResponseStream();
    reader = new StreamReader(stream);
    try { strResponse = reader.ReadToEnd(); } 
    finally { reader.Close(); }
    resp = null;
  }
  catch (Exception ex) { 
    this.output_response("::" + ex.Message); 
  }
  finally { 
    if (resp != null) resp.Close();
  }
  return strResponse;
}


///
/// Example of HTTP Post request.
/// Call the following function: e.g. 
/// string html = HttpPost("http://abcde.com", "a=1&b=2");
///
private string HttpPost(string URI, string Parameters) 
{
  WebRequest req = WebRequest.Create(URI);
  //req.Proxy = new System.Net.WebProxy(ProxyString, true);

  req.ContentType = "application/x-www-form-urlencoded";
  req.Method = "POST";

  byte [] bytes = System.Text.Encoding.ASCII.GetBytes(Parameters);
  req.ContentLength = bytes.Length;

  Stream os = req.GetRequestStream ();
  os.Write (bytes, 0, bytes.Length); 
  os.Close ();

  WebResponse resp = req.GetResponse();
  if (resp== null) return null;

  StreamReader sr = new StreamReader(resp.GetResponseStream());
  return sr.ReadToEnd().Trim();
}


///
/// Example of using HTTP Post to log into a site.
///
private void login() {
  HTMLDocument myDoc = new HTMLDocumentClass();
  myDoc = (HTMLDocument) axWebBrowser1.Document;

  try 
  {
    HTMLInputElement oUser = null, oPass = null;

    oUser = (HTMLInputElement) myDoc.all.item("username", 0);
    oPass = (HTMLInputElement) myDoc.all.item("password", 0);

    if (oUser == null || oPass == null) return;

    oUser.value = "username_value";
    oPass.value = "password_value";

    HTMLFormElement frm = (HTMLFormElement) myDoc.all.item("login", 0);
    frm.submit();

    this.Task = 1; 
  } 
  catch (Exception ex) 
  {
    this.showInfo("test() error: " + ex.Message);
  }
}


///
/// Example of using HTTP Post to download an Excel file.
///
private void getExcel() {
  HttpWebResponse resp = null;
  Stream stream;
  string filename = this.downloadFolder + "/download.xls";

  try 
  {
    wr = (HttpWebRequest) WebRequest.Create(this.excel_url);
    wr.Method = "POST";
    wr.ContentType = "application/x-www-form-urlencoded";
    wr.ContentLength = byteArray.Length;
    wr.Timeout = 100000; // in ms. Set this bigger than the site timeout value.
    MyUtil.appendLog("wr.contentlength: " + wr.ContentLength);

    wr.CookieContainer = new CookieContainer();
    wr.CookieContainer.SetCookies(new Uri(this.excel_url) , 
        ((mshtml.HTMLDocumentClass) this.axWebBrowser1.Document).cookie.ToString());
    MyUtil.appendLog("cookie: " + 
        ((mshtml.HTMLDocumentClass) this.axWebBrowser1.Document).cookie);

    // Send post request
    Stream dataStream = wr.GetRequestStream();
    dataStream.Write(byteArray, 0, byteArray.Length);
    dataStream.Close();
    resp = (HttpWebResponse) wr.GetResponse();
    resp.Cookies = wr.CookieContainer.GetCookies(resp.ResponseUri);
    MyUtil.appendLog("resp status: " + resp.StatusDescription);

    stream = resp.GetResponseStream();

    //MyUtil.appendLog("resp header: " + resp.ContentType );
    // Header: usually 'txt/html'. here is 'application/vnd.ms-excel'
    StreamReader reader = new StreamReader(stream);
    try 
    {
      MyUtil.saveFile(filename, reader.ReadToEnd());
      this.downloadSucceed = true;
    } 
    catch (Exception ex) 
    { 
      MyUtil.FileDelete(filename);
      this.downloadSucceed = false;
    }
    finally 
    {
      reader.Close();
    }
  } 
  catch (Exception ex) 
  {
    this.downloadSucceed = false;
    MyUtil.FileDelete(filename);
  } 
  finally 
  {
    if (resp != null) { resp.Close(); }
  }
}

///
/// Another way of navigating website: use the axWebBrowser control.
///
this.axWebBrowser1.Navigate(url);

[1] The user32 SendInput windows API. The SendInput function synthesizes 
    keystrokes, mouse motions, and button clicks to the currently active window. 
[2] Capturing binary download via code through axwebbrowser1.

Per capita revenue of high tech companies

Here is an article on per capita revenue of some high tech companies (In Chinese).

Here's the list of world's largest public and private business's gross annual revenue, number of employees and other information.

It is interesting to see the data.

Sams Teach Yourself TCP/IP in 24 Hours

Sams Teach Yourself TCP/IP in 24 Hours (4th Edition) - by Joe Casad, 2008, 456 pages. ISBN-10: 0672329964.

I caught this book in sight at Barns and Noble. It is a short book to read, to the point and clear on basic concepts. Short is good.

I. TCP/IP basics

II. TCP/IP Protocol system

2. Correspondence of TCP/IP model and OSI model.
  TCP/IP                      OSI         Relevant protocols
  ----------------------------------------------------------------------------------
  Application layer           A,P,S          
  Transport layer             T           TCP/UDP
  Internet layer              N           IP, ARP, RARP, ICMP, router(RIP, OSPF etc.)
  Network access layer        D,P         FTS, FDDI, PPP, 802.11, 802.3, 802.16

  note: 802.3 - ethernet, 802.11 - wireless, 802.16 - winmax

3. Network access layer
  - physical addressing.
  - LAN - ethernet.
    CSMA/CS (Carrier Sense Multiple Access with Collision Detect)
    ethernet frame: preamble|dest addr|sr addr|length|data|FCS(CRC)

4. Internet layer
  - IP, IP header
  - IP addressing: class A(8/24), B(16/16), C(24/8), D, E
  - ARP (Address Resolution Protocol)
  - RARP (Reverse ARP)
  - ICMP
  - BGP (Border Gateway Protocol), RIP (Routing Information Protocol)

5. Subnetting & CIDR (Classless Inter-Domain Routing)
  - subnet mask/host ID
  - split and combine networks.

6. Transport layer
  - TCP/UDP
  - ports, sockets
  - multiplexing, demultiplexing.
  - TCP: stream, resequencing, flow control, precedence & security, graceful close.

7. Application layer
  - use socket/port to communicate with transport layer.
  - target of multiplexing/de-multiplexing

III. Networking with TCP/IP

8. Routing
  - routing table
  - IP forwarding
  - Dynamic routing algorithm
    - DV (Distance vector). e.g. RIP
    - LS (Link state). e.g. OSPF (Open Shortest Path First)
      LS is more popular than DV now.
  - Complex network routing
    1) core router - backbone network (GGP)
    2) exterior router - on border of autonomous systems (EGP: e.g. BGP)
    3) interior router - within autonomous system (IGP: OSPF/RIP)
  - classless routing: CIDR.
  - OSPF: implemented as routed on unix/linux, builds SPT (Shortest Path Tree)

10. Firewall
  - DMZ (Demilitarized Zone)
  - rules
  - proxy service
  - reverse proxy

11. Name resolution
  - DNS (Domain Name Server)

IV. TCP/IP utilities.

V. TCP/IP and the internet

18. Email
  - outgoing email: SMTP
  - incoming email: POP3/IMAP

19. Streaming and casting
  - stack:
    RTP
    UDP
    Internet layer
    Network Access layer

VI. Advanced topics

C Traps and Pitfalls

C Traps and Pitfalls - by Andrew Koenig, 1989, 160 pages. ISBN-10: 0201179288.

Andrew Koenig wrote a small reference manual on C programming based on his experience when he worked at AT&T lab. Since it received wide acceptance, he added more material and resulted in this book. It's highly recommended to any serious C programmers. Some contents are kind of outdated, such as those about problems of early day compilers. But many points are still ubiquitously applicable.

- Introduction

- Chapter 1. Lexical pitfalls
  1.3 greedy principle in evaluating statement.
      e.g. a --- b is: a-- - b, 
           y = x/*p is: y=x plus the start of a comment! 
                        Should write as y = x / *p or y = x / (*p).
           a +++++ b is: a++ ++ + b. This has compile error since a++ is not l-value.
      Be careful, if a number starts with 0, it's an octal number.

- Chapter 2. Syntax pitfalls
  2.1 Function declaration.
      This casts address 0 as the pointer to function void f() and call it.
      (* (void (*)()) 0)(); 
  2.2 Operator precedence.
      if (a == 'a' || b = 'b' || c == 'c') {} is equivalent to:
      if ((a == 'a' || b) = ('b' || c == 'c')) {}
  2.6 dangling else.
      if (a) 
        if (b) b ++;
      else { c ++; }
      is equivalent to:
      if (a) {
        if (b) b ++;
        else { c ++; }
      }

Chapter 3. Semantic pitfalls
  3.6 off-by-1 error - is the most prevalent.
      One solution in C: 0-based C array, using asymmetric boundary.
      e.g. x >= 16 && x < 38. 38-16 is exactly the size of the range.
  3.9 Check overflow.
      method 1: if ((unsigned) a + (unsigned) b > INT_MAX) // overflowed
      method 2: if (a > INT_MAX - b) // overflowed

Chapter 4. Linking
  lint.

Chapter 5. Library functions
  5.1 int getchar() - return types does not match function, can cause problem.
  5.2 I/O buffer. 
      setbuf(stdout, (char *) 0); // no buffer
  5.4 errno
  5.5 signal, longjmp

Chapter 6. Preprocessor
  - macro
  - use of -- or ++ can cause unexpected side effects in macro.
  6.3 assert
      #define assert(e) \
              ((void) ((e) || _assert_error(__FILE__, __LINE__)))

Chapter 7. Portability
  7.5 >> and divide by 2. >> is faster and works correctly when var is positive.
      e.g. replace "mid = (left + right) / 2" with "mid = (left + right) >> 1".
  7.11 literal string can represent an array.
      e.g. "0123456789"[n%10] is equivalent to: a[] = "0123456789"; a[n%10];
           This is used in systems where 0-9 may not be consecutive.

Chapter 8. Suggestions and answers.
  - Optimize binary search: 
    1) use >> instead of 1/2, 2) use pointer instead of array indexing.
  - Little/big ending.
  - getchar(), putchar() have both macro and function definitions. macro is faster.
  - atol().

Appendix A
  - printf. %p, %n, %06d is equivalent to %.6d in most cases.
  - varargs
  - stdarg

Author's suggestions on using C++:
  - avoid pointer
  - use library
  - use class

Smale's Sphere Eversion Paradox

Interesting video demonstrates the process and explains why.

Some algorithm/system resources

- A Collection of Dice Problems. For probability issues.
- Lock free algorithms.
- Sorting and searching
- The Art of Debugging with GDB, DDD, and Eclipse. For debugging multi-threaded applications.
- A Memory Allocator. About implementation of malloc() etc.
- Some Storage Management Techniques for Container Classes. C++ stuff.
- Beej's Guide to Network Programming Using Internet Sockets. One page guide.
- Some interview questions.
- Technical Interview Blog (Java, 2007)