C++ tricks from Jim Brooks

C++ Programming

Index C++ Tricks STL Code Snippets Stream Code Snippets Redirecting Streams Overloaded Operators Defining operator<<() C++ Pitfalls & Traps STL Pitfalls & Traps C Preprocessor Tricks Please click here if you notice any mistakes or have additions.

C++ Tricks // To turn a fundamental type into a (somewhat) distinct type. #define DECLARE_DISTINCT_TYPE( CLASS, T ) \ class CLASS \ { \ public: \ CLASS( T val ) : mVal(val) { } \ operator T() const { return mVal; } \ CLASS& operator=( const T& val ) { mVal = val; return *this; } \ private: \ T mVal; \ }; DECLARE_DISTINCT_TYPE( Radian, float ) DECLARE_DISTINCT_TYPE( Degree, float ) void Rotate( Radian rad ); // these overloaded functions become possible void Rotate( Degree deg ); // yet can be manipulated as floats

STL Code Snippets // Vector: vector vec; vec.push_back( name ); // push_back() means append vec.clear(); // Iterating thru a container: vector files; vector::iterator itr; for ( itr = files.begin(); itr != files.end(); ++itr ) cout << *itr << endl; // Iterating by subscript using an index (N/A to associative containers): vector vec; for ( int i = 0; i < vec.size(); ++i ) // Building and iterating thru a map and using pairs: map mp; mp.insert( pair( "a", 1 ) ); mp.insert( pair( "b", 2 ) ); mp.insert( pair( "c", 3 ) ); map::iterator itr; for ( itr = mp.begin(); itr != mp.end(); ++itr ) cout << itr->first << " " << itr->second << endl; // To test if a key exists in a map/set: if ( mMap.find(key) != mMap.end() ) // Adding then removing from a container. list l; for ( int i = 0; i < 10; ++i ) l.push_back( i ); // append while ( ! l.empty() ) { // Prints/pops oldest (head) element first, cout << l.front() << endl; l.pop_front(); } // If no match. if ( map.find("key") == map.end() ) cout << "not found" << endl; // Print a container. list con; copy( con.begin(), con.end(), ostream_iterator(cout," ") ); // Copy a container: copy( con1.begin(), con1.end(), con2 ); // WRONG/PITFALL if con2 smaller than con1 con2.clear(); copy( con1.begin(), con1.end(), back_inserter(con2) ); // OK if con2 smaller than con1 // Sorting using a binary predicate: // An alternative (using the container container pointers instead // of values) that doesn't need a binary predicate is to define // your own operator<() which sort() uses by default. bool BinPred( const Class& o1, const Class& o2 ) { return o1.val < o2.val; } vector vec; sort( vec.begin(), vec.end(), BinPred ); // A function that returns a pair. // The pair is returned by value (like a struct would be, so it isn't dangling). std::pair AddMul( float x, float y ) { std::pair res; res.first = x + y; res.second = x * y; return res; } // Print a binary number in base 2 using bitset. #include bitset<8> val = 0xff; cout << val; // Turn string to all upper-case. string s; transform( s.begin(), s.end(), s.end(), toupper ); // Distance between two iterators. distance( itr1, itr2 ) // Getting the iterator of an item that was inserted into a map: // (a multimap/multiset differs, adapted from gfx_share.hh) std::pair insertion; insertion = mMap.insert( std::make_pair( *obj, std::make_pair(copy,1) ) ); itr = insertion.first; // insertion is assumed to succeed (bool not checked) // Replacing/substituting chars of a string. // string::replace() is really an overwrite, not a substitution. char Unix2DosDirChar( char c ) { return c == '/' ? '\': c; } string Unix2DosDir( const string& dirname ) { string s = dirname; std::transform( s.begin(), s.end(), s.begin(), Unix2DosDirChar ); return s; }

Stream Code Snippets // Save/restore stream flags. std::ios::fmtflags savedFlags = cout.flags(); ... cout.flags(savedFlags); // showbase (eg automatically print "0x" prefix for hex, etc). cout.setf( std::ios::showbase ); // Set float precision. mStream.setf( ios::fixed, ios::floatfield ); mStream.precision( 20 ); // Writing to an integer to a stream using width/precision. // Note that width/precision is discarded after every call to stream object! std::cout << std::setw(5) << std::setfill('0') << x << ' '; std::cout << std::setw(5) << std::setfill('0') << y << ' '; std::cout << std::setw(5) << std::setfill('0') << z << ' ' << std::endl; // Convert an int to a string stream for the purpose // of passing the int as a C++ string. int i; ostringstream ss; ss << i; Print( ss.str() ); // Open for reading to test if file is empty. strm.open( fname, ios::in|ios::binary ); if ( strm.good() && strm.is_open() ) { // File exists. Is it empty? strm.seekg(1); char c; strm >> c; // a read is required to trigger EOF, seekg(1) alone won't if ( strm.eof() ) cout << "File exists and is empty." << endl; else cout << "File exists and contains data." << endl; } else { cout << "File doesn't exist." << endl; } // Reopen in R/W mode. strm.close(); strm.clear(); strm.open( fname, ios::in|ios::out|ios::trunc|ios::binary ); strm.seekp(0);

Redirecting Streams To write a class that redirects a stream to something else, define your own streambuf class, then construct an ostream with pointer to the streambuf object. An example is in Nicolais Josuttis's STL book. A faux-pas is trying to derive from ostream (see prog/c++/streamRedirectionFauxPas.cc). One problem is that passing endl will result in a "bad cast&qout; exception (g++ 3/4). http://shekel.jct.ac.il/cc-res/online-doc/libgPP/iostream_28.html http://www.lysator.liu.se/c/bs-errata-1.html http://gcc.gnu.org/onlinedocs/libstdc++/27_io/howto.html#6

Defining operator<<() The idea is to overload operator<<() with your user-defined type. class Point { public: int x, y; }; ostream& operator<<( ostream& strm, const Point& obj ) { strm << "(" << obj.x << "," << obj.y << ")"; return strm; }

Overloaded Operators Overloaded operators, except assignment, are inherited. But subtle compiler errors can occur. Let's say you have two related classes that are logically different types, but are structurally equivalent (identical members). class Vertex { public: Vertex& operator+( const Vertex& src ); float x, y, z; }; class WorldVertex : public Vertex { public: }; Now try adding two derived objects: void Draw( const WorldVertex& v ); WorldVertex v1, v2, v3; v3 = v1 + v2; // compile error Draw( v1 + v2 ); // ok Some compilers will give obscure errors, leading you to think that you need to duplicate all the overloaded operator code into every derived class. That wouldn't ideal. What's happening in v3 = v1 + v2 is that Vertex::operator+() is called which returns a base Vertex object, not a derived WorldVertex object. You might think assigning a base object into a derived object is an immediate error. But the C++ compiler first tries to find the matching assignment operator such as Derived& operator=( const Base& ): class WorldVertex : public Vertex { public: WorldVertex& operator=( const Vertex& src ) { x = src.x; y = src.y; z = src.z; return *this; } }; Because these classes are structurally equivalent, Derived& operator=( const Base& ) does make sense, as it can simply copy .x, .y, .z.

C++ Pitfalls & Traps C++ has a zillion pitfalls, this lists some of the worst. Reusing or abusing assignment operator=() in a copy constructor: This pitfall exists with more complex classes whose members aren't fundamental types. Assignment operators should free members before reassigning them. If an operator=() that frees resources is called in a copy constructor, it will try to free garbage. A solution is have separate Copy() and Free() methods. class Class { public: Class( const Class& src ) { *this = src; // the temptation to write terse code leads to a pitfall } Class& operator=( const Class& src ) { delete mObj; // free members mObj = src.Obj; // reassign members return *this; } private: Class2* mObj; }; Method overriding will fail if you forget to write virtual by a method in base class or the function signatures differ. Calling a virtual method from a base constructor. Think about the order of construction: the derived object hasn't been constructed yet. Default copy constructors or assignment operators may cause trouble. Safegaurds writing a dummy default copy constructor as private and/or with assert(0). A constructor with a single arg might be misinterpreted as a conversion operator. Use the keyword explicit if conversion isn't desired. Class( int ); int n; Class obj = n; // converts an int to a Class obj !! Temporary objects and reference args void Byref( int& x ) { ... x = y; } Byref( a + 2 ); // oops, result went nowhere into a temp operator bool() operator bool() is seductive for tersely testing if an object is valid: class Data { public: operator bool() const { return mValid; } private: string mData; }; void Process( Data& data ) { // Valid data? if ( data ) { } } Let's say two objects are valid but their values (members) differ. if ( data0 == data1 ) return; You'd think return won't happen. But it will. This is what's compiled: if ( bool(data0) == bool(data1) ) return; // true == true The pitfall is implicit conversion. The class doesn't define operator==(). But the compiler doesn't supply a default memberwise comparison as you might assume. Rather, the compiler implicity converts both operands to bools. Because that's precisely what operator bool() is for.

STL Pitfalls & Traps end() for ( itr = files.begin(); itr < files.end(); ++itr ) // WRONG for ( itr = files.begin(); itr != files.end(); ++itr ) // ok reserve() vs. resize() resize() expands the container -- reserve() doesn't! Incrementing iterators while ( itr++ != files.end() ) // WRONG, itr incremented past end Short destination containers This could be a bug if vec2 is shorter than vec. copy() won't extend the destination container. copy( vec.begin(), vec.end(), vec2.begin() ); One solution is: vec2.resize( vec1.size() ). Another is to use an insert iterator (insertor): copy( vec.begin(), vec.end(), back_inserter(vec2) ); Catenating a string with a char char baseName[] = "myfile"; string suffix = "txt"; string fileName = baseName + '.' + suffix; // WRONG This is wrong because the compiler misinterprets this as C's way of adding an integer to a pointer rather than as C++ string catenation. That is, the compiler's intepretation is: string fileName = &baseName[ int('.') ] + suffix;

C Preprocessor Tricks Macro to expand a unique name: // Arcane indirect trick to give a variable a unique name. // Subtlety: If written on the same line, UNIQUE_NAME() expands the same name. #define UNIQUE_NAME__(NAME,LINE) NAME##LINE #define UNIQUE_NAME_(NAME,LINE) UNIQUE_NAME__(NAME,LINE) #define UNIQUE_NAME(NAME) UNIQUE_NAME_(NAME,__LINE__)

home © 2007 Jim Brooks Last modified: Thu May 24 14:11:14 EDT 2007

keywords: C++ STL programming language, C++ STL resources, C++ tricks recipes, Standard Template Library, C++ common phrases expressions idioms, C++ code snippets, C++ pitfalls traps quirks caveats, programming tricks, GNU gcc g++,

What is embedded database

from dbazine.com

Embedded Database Primer

• 
• 

by James F. Koopmann

Introduction

If you’re anything like me, staying on top of current trends within the field of database administration is highly challenging at times. We are continually bombarded with new trends and technology that we cannot normally afford to try. For quite awhile, I have wondered what embedded databases were all about. I think of embedded databases as something small and contained in my cellular phone or as maintaining some information within my automobile. But what is the embedded database world really like?

I decided to reduce my learning curve and develop a primer about embedded databases by interviewing a vendor with this expertise. I posed a few high-level questions to Steve Wampler, Director of Database Marketing, Birdstep Technology who has worked successfully with embedded databases for some time:

Q. What exactly defines an embedded database?

We define an embedded database as a software component that is part of the application, not a separate running application. Its operations are invoked by the application. Another way to look at it is that embedded databases are embedded within an application.

Q. Can you explain to the layman how a database is embedded within an application?

It is embedded either as in-line code or linked libraries. In either case, it's code that is executed only when invoked by the application.

Q. How long has the embedded database industry been around?

More than 20 years — one could argue that since the beginning of software, embedded databases have been in existence.

Q. What drives the new features introduced in the embedded industry?

This is vendor-dependent. What you are seeing today is an application view for development — meaning features are being developed to do certain application tasks.

Q. What is the fastest growing business use for embedded databases?

One of the hottest is automotive.

Q. Does the embedded database community compete with the larger RDBMS vendors and in what regards?

In some cases, yes. One needs to look at the database market as a continuum with the embedded on one end and the enterprise on the other. There is a point in the continuum where the embedded databases are competing with the enterprise databases. Typically, this is a case where the plethora of features in enterprise databases is more important than the cost, size, and performance. These last three factors are the key advantage of embedded database over enterprise database.

Q. How do embedded databases differ from the typical relational databases such as Oracle, DB2, and SQL Server?

These databases are big, expensive, and slow. They are general purpose because they must serve a wide range of applications and users. They tend to be separate running applications that are independent of the system application.

Q. What are the top three features or business solutions for embedded databases?

Performance, small size, and price.

Q. Are embedded databases relational?

Yes. There are databases that are hierarchical (network model, XML model) as well.

Q. What is the Network Data Model?

The relational database model establishes and maintains inter-record relationships through common data fields. The Network Database Model establishes inter-record relationships directly, through physical links between the related records, rather than through common data fields.

Q. What applications are better suited for embedded databases?

Application-specific systems that have no or limited human administration or interruption.

Q. What type of applications are not meant for embedded databases?

Large enterprise systems.

Q. Are there any instances where you have seen successful conversions from major RDBMS vendors to an embedded database system?

Usually in business automation systems where the database needs to handle large data, multiple users, but can't be too expensive and must be allowed to be redistributed by the developer.

Q. What are the administration duties for maintaining an embedded database environment?

These are minimal because the application is usually the administrator.

Q. What are the tuning opportunities of an embedded database? Is there much a DBA can do for such a small footprint?

It depends on the functionality of the database. In our case, tuning can come through cache management (performance), using SQL or Native API (performance), user-defined procedures and functions.

Q. How exactly do embedded databases speed time to delivery of applications and cut development costs?

Every software application manages data. In most cases, the data is managed in a flat file — and this is fine for these applications as long as they have a short life cycle and their data is stagnant. If the application is going to have a long life cycle and/or going to grow in its use, having a database management system is 100 times cheaper to buy than to build and in many years quicker to develop.

Q. How robust is the availability, reliability, and recoverability of embedded databases?

Very robust — because of their applications, this is a must.

Q. When I hear high performance for embedded databases I immediately think they surely cannot keep up with the “big boys” in relational databases. What can we expect as far as performance from an embedded database?

This is highly dependent on if the application is mostly reading, writing, updating, etc. Typically you can find order-of-magnitude better performance in embedded database.

Q. Are there any typical limits to the size of an embedded database such as data size, footprint, or instruction set?

No.

Conclusion

Embedded databases differ from typical databases such as DB2, Oracle, and SQL Server in that it is completely integrated into the application or hardware device in such a way that the end-user has very little knowledge, if any, of its existence. Users and administrators are not burdened with time-consuming installations or maintenance as the database is literally packaged with the application and should be self maintaining.

Embedded databases are meant to run on many different platforms with various programming interfaces. The nature of embedding databases’ instruction sets being linked specifically within and for a specific application gives them a small footprint. A reduced instruction set allows them to achieve performance that is hard to beat. Surely, you wouldn’t want to put an Oracle instance within your cellular phone, but I might in my automobile.

--

James F. Koopmann is dedicated to providing technical advantage and guidance to companies within information technology. Over the years, James has worked with a variety of database-centric software and tools vendors as strategist, architect, DBA, and performance expert. He is an accomplished author appearing regularly within printed publications across the Web, and speaking at local area User Groups as well as industry conferences. He may be reached at jkoopmann@pinehorse.com or www.pinehorse.com.

Interesting People

I wish I could meet these fabulous people one day :)

http://en.wikipedia.org/wiki/Eliot_Spitzer
http://en.wikipedia.org/wiki/Shirley_Ann_Jackson
http://en.wikipedia.org/wiki/Padmasree_Warrior

Good Investment Books

1. Intelligent Investor (Benjamin Graham)
http://www.amazon.com/Intelligent-Investor-Book-Practical-Counsel/dp/B0002X1JKU/ref=pd_bbs_sr_1/104-2886434-5656728?ie=UTF8&s=books&qid=1193986477&sr=8-1

Prompt for linux

Hit upon the basics of linux shell, (will add more)

1. export PS1="[${LOGNAME}@$(hostname)] # "

Diff between only specified lines in unix

diff < (sed ' line1,line2!d' file1) < (sed 'line1,line2 !d' file2)

Converting Numbers to Strings and Strings to Numbers in C++

http://www.parashift.com/c++-faq-lite/misc-technical-issues.html

Managing C++ Objects

http://billharlan.com/pub/papers/Managing_Cpp_Objects.html

Managing C++ Objects

Here are some guidelines I have found useful for writing C++ classes. There are many good books on the subject, but they have not been sufficient to keep me out of trouble. The first time I returned to writing C++ after a year of writing Java, I was appalled at how much my design was constrained by managing the lifetime of objects. When C++ classes share objects, then they must negotiate who owns the object. Garbage collection is not available, and smart pointers often fall short.
§ Simple constructors

If your preferred constructor takes arguments, then define a default constructor (no arguments) and make it protected. Derived classes will require this method.

Define protected initialization methods void init(...) with arguments, and call them from your preferred constructors. Each initialization method should set all member variables to a valid state, without relying on constructor initialization blocks. Use these initialization methods from your public copy constructor and assignment operator, if required.

Remove everything from constructor initialization blocks except the simplest constructor of a superclass (preferably a default constructor). Call protected superclass initialization methods from the subclass initialization methods. Make initialization methods non-virtual to avoid hiding by derived classes (since the name will always be init(...).)

All init(...) methods should first call the init() equivalent of a default constructor, to initialize all member pointers, perhaps to nulls. If your constructor fails and throws an exception, then the destructor can be called safely.

Your constructors will now be much more flexible and robust. Derived class constructors can manipulate their arguments before initializing the superclass. (Superclass constructors can only be called in initialization blocks.) Within a single class, you can share more initialization between alternative constructors. You need not worry about the order of initialization blocks.
§ Implement "The Big Three"

Always define a copy constructor and an assignment operator. Don't let anyone use the default implementations. If your class contains pointers to objects which your class does not plan to delete, then just make these two methods private, without an implementation. Do not implement versions that make shallow copies. You do not want a user to accidentally make copies on the stack if required to call a non-copy constructor or clone method instead. Making copies of objects should be a very deliberate step Conversion operators (single-argument constructors) can be dangerous for the same reason.

Define a virtual destructor unless you never want anyone to derive from your class. Define a protected non-virtual void dispose() method that deletes the object's resources, then call this method from your destructor. (This is the destructor equivalent of an init() method.) You can use this method in assignment operators, initialization, and derived classes.
§ No references as members

A class member should never be a reference, whether const or non-const. A member's object reference can only be set in the initialization block of a constructor. You will not be able to set a reference member in an initialization method. A reference permanently prevents your class from replacing the object dynamically.
§ Optional ownership

If a constructor or initialization method takes a non-const object as an argument, then you must decide whether this wrapper class will assume ownership of this object. The destructor of a Bridge or Decorator class might need to delete the contained object. Or maybe not. If you have any doubt, then the constructor should allow the user to choose.
§ No pointers as arguments

Pass all objects to class methods and constructors as references. There is absolutely no advantage to passing objects as pointers. This rule is equally valid whether the objects are const or not.

I've already recommended that all class members be saved as pointers. You can easily take the address of an argument reference (with an ampersand) and assign it to your member pointer. Some C++ programmers do not seem to realize that the address of a reference is the same as the address of the original object. So they pass pointers when they want to save the argument, and references when they do not. This is a poor form of documentation, based on a misunderstanding.

If an object is passed to a constructor or initialization method, the user can expect the class to hang onto it. If a method saves an object from an argument, choose an appropriate name, like setColor(Color&) or addInterpolator(Interpolator&).

The worst excuse for using a pointer as an argument is that you want to give it a default value of null (0). You still have to document what a null object is supposed to mean. Worse, the user may overlook that the argument exists or is optional. Declare a separate method that lacks the extra argument. The effort is negligible.
§ Returning objects

One can always return objects from class methods by reference, either const or non-const. A user can take the address of the reference, if necessary, to save the object. But there are no drawbacks to returning objects always as pointers. Consistency is preferable, and most API's return pointers.

If you return an object allocated on the heap (with a new), then be clear who has ownership of the object--your class, the recipient, or a third party.

Think about whether you are breaking encapsulation of member data in a way that will prevent modification later.

Never return a reference to a class member allocated on the stack in the header file. If your class replaces the value, then the user may be left with an invalid reference, even though your object still exists. (Other reasons: Your class will never be able to remove the object as a member. A user may manipulate the logic of your class in unexpected ways.)

A method should modify an object constructed by the user by accepting it as a non-const reference. Returning the same object would be redundant and confusing.
§ Clean header files

A header file ideally includes only the header file of super-classes or of standard C++ libraries. All other classes can be forward declared, like class ClassName; or template class ClassName;. Forward declarations will greatly simplify your "make" dependencies and speed your builds. Repairs will be easier.

Member variables that are saved by value require your header to include another header file. Consider allocating such members on the heap, even if you must delete them in the destructor. Save member objects by value only when the default constructor creates a lightweight object with a useful state.

If you have reasons to put your entire implementation in the header file, then of course you cannot take advantage of forward declarations.
§ Write more Java

When you get a chance, write more Java to free your mind of such distractions. Your C++ will improve.
§ Examples

See an illustration of some of these patterns in [ ../code/cpp_prototype ] .

Bill Harlan

1998

Revision: 1.21 2004/09/14 18:01:26 harlan Exp $

Return to parent directory.

Process start time in Unix

To find the start time of a process in unix use

ps -fu

zgrep "tosearch" *.gx | tr ',' '\12' | grep "tosearch"

Thread Safe and Thread Aware

From codeproject.com(http://www.codeproject.com/csharp/syncroot.asp)

Thread aware:

At any given time, at most one thread can be active on the object. The object is aware of the threads around it and protects itself from the threads by putting all the threads in a queue. Since there can be only a single thread active on the object at any given time, the object will always preserve its state. There will not be any synchronization problems.
Thread safe:

At a given time, multiple threads can be active on the object. The object knows how to deal with them. It has properly synchronized access to its shared resources. It can preserve its state data in this multi-threaded environment (i.e. it will not fall into intermediate and/or indeterminate states). It is safe to use this object in a multi-threaded environment.

Using an object that is neither thread-aware nor thread-safe may result in getting incorrect and random data and mysterious exceptions (due to trying to access the object when it is being used by a thread and is in an unstable, in-between state at the instant of access of the second thread).

Efficient VIM editing

http://jmcpherson.org/editing.html

Good Hash Discussion

http://burtleburtle.net/bob/hash/doobs.html

Timers in C#

From msdn2.microsoft.com
private void CreateTimer()
{
System.Timers.Timer Timer1 = new System.Timers.Timer();
Timer1.Enabled = true;
Timer1.Interval = 5000;
Timer1.Elapsed +=
new System.Timers.ElapsedEventHandler(Timer1_Elapsed);
}

private void Timer1_Elapsed(object sender,
System.Timers.ElapsedEventArgs e)
{
System.Windows.Forms.MessageBox.Show("Elapsed!",
"Timer Event Raised!");
}

Berkeley DB

From : http://pybsddb.sourceforge.net/ref/intro/terrain.html
1. Berkeley DB is an embedded database that supports fairly simple data access with a rich set of data management services

Data access in this context means
a) insert b)update c)search d)delete
Data management in this context means that
a)Concurrency b)Transactions c)Recovery

Unix Ports

From Google groups

netstat -lp

It will tell you which task is listening on the port.

fuser -v -n tcp 32768

Will tell you which task is listening on the specified port and under
which account it's running.

IE6 duh?

urns out, IE doesn't like the script tags if they are using element minimization. I got the page rendering just as I intended by changing the tag to look like this:



Doing some research, I came across this post in theList by Eric Vitiello which clarifies this more. Apparently the DTD declaration for the script tag says , and the XHTML specs says (under Appendix C. 3):

Given an empty instance of an element whose content model is not EMPTY (for example, an empty title or paragraph) do not use the minimized form (e.g. use

and not

).

So, I guess this isn't really a bug in IE. I'd think instead, that this is a bug in the DTD itself. The script tag doesn't have to contain #PCDATA (in fact, I consider it graceful if it doesn't), and forcing it is, well, stupid.

For now, I am explicitly closing the script tag with a seperate closing tag, and everything seems to be working well. Does anyone have any idea about handling this better, preferably with minimized element closures

stolen from piecesofrakesh.blogspot.com

When do you need a pointer to a reference?

From C++ groups
> Why/when would someone need a pointer to a reference?

Never. A reference is another name for a real thing. A pointer can only
point to a real thing - it can't point to a name for a real thing.

References are often implemented as secret pointers, but it breaks the
language if you try to get a handle on this secret pointer - it is an
implementation detail.

If you meant a reference to a pointer, use this when you need something to
grab your pointer, point it to something else, and give the result back to
you. Consider a parser that reads statements written by the user:

WORD_TYPE getWord (char *&statement);

Each time you call this function it finds a word, returns its type, and
points the pointer off the end of the word.

VIM split

Vim viewport keybinding quick reference

:sp will split the Vim window horizontally. Can be written out entirely as :split .

:vsp will split the Vim window vertically. Can be written out as :vsplit .

Ctrl-w Ctrl-w moves between Vim viewports.

Ctrl-w j moves one viewport down.

Ctrl-w k moves one viewport up.

Ctrl-w h moves one viewport to the left.

Ctrl-w l moves one viewport to the right.

Ctrl-w = tells Vim to resize viewports to be of equal size.

Ctrl-w - reduce active viewport by one line.

Ctrl-w + increase active viewport by one line.

Ctrl-w q will close the active window.

Ctrl-w r will rotate windows to the right.

Ctrl-w R will rotate windows to the left.

From Linux.com

Javascript :quirkmodes.org

http://www.quirkmodes.org

CRON

minute hour dom month dow user cmd

minute This controls what minute of the hour the command will run on,
and is between '0' and '59'
hour This controls what hour the command will run on, and is specified in
the 24 hour clock, values must be between 0 and 23 (0 is midnight)
dom This is the Day of Month, that you want the command run on, e.g. to
run a command on the 19th of each month, the dom would be 19.
month This is the month a specified command will run on, it may be specified
numerically (0-12), or as the name of the month (e.g. May)
dow This is the Day of Week that you want a command to be run on, it can
also be numeric (0-7) or as the name of the day (e.g. sun).
user This is the user who runs the command.
cmd This is the command that you want run. This field may contain
multiple words or spaces.

AJAX the Diagram

http://www.adaptivepath.com/images/publications/essays/ajax-fig1.png

STL:Map

from metashell.com
#pragma warning(disable: 4786)


#include
#include
#include

using namespace std;

int main() {
map ass_array;

// Assign keys and values

ass_array["fat"] = 0;
ass_array["sodium"] = 45;
ass_array["totalcarb"] = 46;
ass_array["protien"] = 0;

// Insert Value

ass_array.insert( map::value_type( "potassium", 25 ) );

// Print value of sodium

cout << ass_array["sodium"] << endl;
cout << "The map has " << ass_array.size() << " entries.\n";

// Iterator used to hold position in the map

map::iterator loc;

// Returns same value as ass_array.end() if not find.

loc = ass_array.find("sugar");

if(loc != ass_array.end())
cout << "Sugar found!\n";
else
cout << "No Sugar\n";

return 0;
}

STL:Sort

From msoe.edu

#include
#include // Include algorithms
using namespace std;

vector vec;
vec.push_back (10);
vec.push_back (3);
vec.push_back (7);

sort(vec.begin(), vec.end()); // Sort the vector

// The vector now contains: 3, 7, 10

STL: find

list nums;
list::iterator nums_iter;

nums.push_back (3);
nums.push_back (7);
nums.push_front (10);

nums_iter = find(nums.begin(), nums.end(), 3); // Search the list.
if (nums_iter != nums.end())
{
cout << "Number " << (*nums_iter) << " found." << endl; // 3
}
else
{
cout << "Number not found." << endl;
}

Sharing mouse and keyboard between two computers with different operating system

from http://synergy2.sourceforge.net

Running Synergy

Synergy lets you use one keyboard and mouse across multiple computers. To do so it requires that all the computers are connected to each other via TCP/IP networking. Most systems come with this installed.

Step 1 - Choose a server

The first step is to pick which keyboard and mouse you want to share. The computer with that keyboard and mouse is called the "primary screen" and it runs the synergy server. All of the other computers are "secondary screens" and run the synergy client.

Step 2 - Install the software

Second, you install the software. Choose the appropriate package and install it. For example, on Windows you would run SynergyInstaller. You must install the software on all the computers that will share the mouse and keyboard (clients and server). On OS X you'll just have a folder with some documentation and two programs. You can put this folder anywhere.

Step 3 - Configure and start the server

Next you configure the server. You'll tell synergy the name of the primary and secondary screens, which screens are next to which, and choose desired options. On Windows there's a dialog box for setting the configuration. On other systems you'll create a simple text file.

Note that when you tell synergy that screen A is to the left of screen B this does not imply that B is to the right of A. You must explicitly indicate both relations. If you don't do both then when you're running synergy you'll find you're unable to leave one of the screens.

Windows
On Windows run synergy by double clicking on the synergy file. This brings up a dialog. Configure the server:

* Click the Share this computer's keyboard and mouse (server) radio button
* Click the Screens & Links Configure... button
* Click the + button to add the server to the Screens list
o Enter the name of server (the computer's name is the recommended name)
o Optionally enter other names the server is known by
o Click OK
* Use the + button to add your other computers
o Using a computer's name as its screen name is recommended
o Choose desired screen options on the Add Screen dialog
* Use the controls under Links to link screens together
o Click (once) on the server's name in the Screens list
o Choose the screen to the left of the server; use --- if there is no screen to the left of the server
o Choose the screens to the right, above and below the server
o Repeat the above steps for all the other screens
* Click OK to close the Screens & Links dialog
* Use Options... to set desired options
* If the server's screen name is not the server's computer name:
o Click Advanced...
o Enter the server's screen name next to Screen Name
o Click OK

Now click Test. The server will start and you'll see a console window with log messages telling you about synergy's progress. If an error occurs you'll get one or more dialog boxes telling you what the errors are; read the errors to determine the problem then correct them and try Test again. See Step 5 for typical errors.

Unix or Mac OS X
Create a text file named synergy.conf with the following:

section: screens
screen1:
screen2:
end
section: links
screen1:
right = screen2
screen2:
left = screen1
end

Replace each occurrence of screen1 with the host name of the primary screen computer (as reported by the hostname program) and screen2 with the host name of a secondary screen computer. In the above example, screen2 is to the right of screen1 and screen1 is to the left of screen2. If necessary you should replace right and left with left, right, up, or down. If you have more than two computers you can add those too: add each computer's host name in the screens section and add the appropriate links. See the configuration guide for more configuration possibilities.

Now start the server. Normally synergy wants to run "in the background." It detaches from the terminal and doesn't have a visible window, effectively disappearing from view. Until you're sure your configuration works, you should start synergy "in the foreground" using the -f command line option.

On unix type the command below in a shell. If synergys is not in your PATH then use the full pathname.

synergys -f --config synergy.conf

On OS X open Terminal in the Utilities folder in the Applications folder. Drag the synergys program from the synergy folder onto the Terminal window. The path to the synergys program will appear. Add the following to the same line, type a space at the end of the line but don't press enter:

-f --config

Now drag the synergy.conf file onto the Terminal window and press enter. Check the reported messages for errors. Use ctrl+c to stop synergy if it didn't stop automatically, correct any problems, and start it again.

Step 4 - Start the clients

Next you start the client on each computer that will share the server's keyboard and mouse.

Windows
On Windows run synergy by double clicking on the synergy file. This brings up a dialog. Configure the client:

* Click the Use another computer's shared keyboard and mouse (client) radio button
* Enter the server's computer name next to Other Computer's Host Name
o This is not the server's screen name, unless you made that the server's host name as recommended
* If the client's screen name is not the client's computer name:
o Click Advanced...
o Enter the client's screen name next to Screen Name
o Click OK

Now click Test.

Unix or Mac OS X
To start a client on unix, enter the following:

synergyc -f server-host-name

where server-host-name is replaced by the host name of the computer running the synergy server. If synergyc is not in your PATH then use the full pathname.

On OS X open Terminal in the Utilities folder in the Applications folder. Drag the synergyc program from the synergy folder onto the Terminal window. The path to the synergys program will appear. Add the following to the same line and press enter:

-f server-host-name

When you added the client to the server's configuration you chose a name for the client. If that name was not client's host name then you must tell the client the name you used. Instead of the above command use this instead:

synergyc -f --name name server-host-name

where name is the name for the client in the server's configuration. (On OS X drag the synergyc program to the Terminal window rather than typing synergyc.)

Step 5 - Test

Clients should immediately report a successful connection or one or more error messages. Some typical problems and possible solutions are below. See the troubleshooting and the FAQ pages for more help.

* failed to open screen (X11 only)

Check permission to open the X display;
check that the DISPLAY environment variable is set
use the --display command line option.

* address already in use

Another program (maybe another copy of synergy) is using the synergy port; stop the other program or choose a different port in the Advanced... dialog. If you change the port you must make the same change on all of the clients, too.

* connection forcefully rejected

The synergy client successfully contacted the server but synergy wasn't running or it's running on a different port. You may also see this if there's a firewall blocking the host or port. Make sure synergy is running on the server and check for a firewall.

* already connected

Check that the synergy client isn't already running.

* refused client

Add the client to the server's configuration file.

* connection timed out

Check that server-host-name is correct.
Check that you don't have a firewall blocking the server or synergy port.

* connection failed

Check that server-host-name is correct.

If you get the error "Xlib: No protocol specified" you're probably running synergy as root while logged in as another user. X11 may prevent this for security reasons. Either run synergy as the same user that's logged in or (not recommended) use "xhost +" to allow anyone to connect to the display.

When successful you should be able to move the mouse off the appropriate edges of your server's screen and have it appear on a client screen. Try to move the mouse to each screen and check all the configured links. Check the mouse buttons and wheel and try the keyboard on each client. You can also cut-and-paste text, HTML, and images across computers (HTML and images are not supported on OS X yet).

Step 6 - Run

Once everything works correctly, stop all the clients then the server. Then start the server with the Start button on Windows and without the -f option on Unix and Mac OS X. Finally start the clients similarly. On Windows before clicking Start you may want to set the Logging Level to Warning so the logging window doesn't pop up (because you currently can't close it, just minimize it).

You can also configure synergy to start automatically when your computer starts or when you log in. See the autostart guide for more information.

Command Line Options Guide

Common Command Line Options
The following options are supported by synergys and synergyc.
-d, --debug level use debugging level level
--daemon run as a daemon (Unix) or background (Windows)
-f, --no-daemon run in the foreground
--display display connect to X server at display (X11 only)
-n, --name name use name instead of the hostname
--restart automatically restart on failures
-1, --no-restart do not restart on failure
-h, --help print help and exit
--version print version information and exit

Debug levels are from highest to lowest: FATAL, ERROR, WARNING, NOTE, INFO, DEBUG, DEBUG1, and DEBUG2. Only messages at or above the given level are logged. Messages are logged to a terminal window when running in the foreground. Unix logs messages to syslog when running as a daemon. The Windows NT family logs messages to the event log when running as a service. The Windows 95 family shows FATAL log messages in a message box and others in a terminal window when running as a service.

The --name option lets the client or server use a name other than its hostname for its screen. This name is used when checking the configuration.

Neither the client nor server will automatically restart if an error occurs that is sure to happen every time. For example, the server will exit immediately if it can't find itself in the configuration. On X11 both the client and server will also terminate if the connection to the X server is lost (usually because it died).

Server Command Line Options

synergys [options]

The server accepts the common options and:

-a, --address address listen for connections on address address
-c, --config pathname read configuration from pathname

address has one of the following forms:

hostname
:port
hostname:port

hostname is a hostname or IP address of a network interface on the server system (e.g. somehost or 192.168.1.100). port is a port number from 1 to 65535. hostname defaults to the system's hostname and port defaults to 24800.

Client Command Line Options

synergyc [options] address[:port]

address is the hostname or IP address of the server and port is the optional netw

Explicit in C++

Using Explicit in C++

In C++ it is possible to declare constructors for a class, taking a single parameter, and use those constructors for doing type conversion. For example:

class A {
public:
A(int);
};

void f(A) {}

void g()
{
A a1 = 37;

A a2 = A(47);

A a3(57);

a1 = 67;

f(77);
}

A declaration like:

A a1 = 37;

says to call the A(int) constructor to create an A object from the integer value. Such a constructor is called a "converting constructor".

However, this type of implicit conversion can be confusing, and there is a way of disabling it, using a new keyword "explicit" in the constructor declaration:

class A {
public:
explicit A(int);
};

void f(A) {}

void g()
{
A a1 = 37; // illegal

A a2 = A(47); // OK

A a3(57); // OK

a1 = 67; // illegal

f(77); // illegal
}

Using the explicit keyword, a constructor is declared to be
"nonconverting", and explicit constructor syntax is required:

class A {
public:
explicit A(int);
};

void f(A) {}

void g()
{
A a1 = A(37);

A a2 = A(47);

A a3(57);

a1 = A(67);

f(A(77));
}

Note that an expression such as:

A(47)

is closely related to function-style casts supported by C++. For example:

double d = 12.34;

int i = int(d);



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5 PHP Design Patterns

Five common PHP design patterns
http://www-128.ibm.com/developerworks/library/os-php-designptrns/?ca=dnw-725

Writing your own newsreader

From:www.indicthreads.com
XML feeds are the way today to keep a tab on what's happening in the blogosphere as well as to know about site updates and new additions. I had heard about two popular open source feature-rich Java APIs to deal with the feeds, ROME and Informa but could never really savor them.

For one of my own sites where I, sort of hand-built the aggregator as Myjavaserevr does not allow deploying external JARs or Taglibs I did not get any chance to play with these APIs. So when I got some opportunity it was imperative that I tried them.

The following is a very elementary example of using the two news aggregation libraries that imitates a newsreader. The examples, as I said, are pretty basic and they would make a hit to the specified Feed URL every time you call the JSPs. The code snippets are not meant to demonstrate good coding practice.

Both the libraries support almost all versions of RSS, RDF and Atom and features such as dynamic discovery of feed format. Feature wise probably Informa has an upper hand (it supports OPML, recognizes the Enclosure element making it suitable to comprehend Podcast feeds and can be configured to use a persistence mechanism built over Hibernate) but what it lacks is availability of documents. There are no primers at the site and the code is very poorly commented making the Javadocs difficult to come to pace quickly. The two Java.net articles that I could, Google have been outdated, as I used the 0.6.5 version of the library.

ROME, on the other hand, has very nice documentation available at its site, complete with code examples. Many desirable features are unfortunately still on the TODO list. For comprehending the "Enclosure" element ROME needs a separate plugin module (that also supports iTunes extensions). While I have not investigated them, there are a number of sub-projects based on both ROME and Informa, for example: there is a JSP Tag library based on Informa. There is a short review of various libraries here but I guess much stuff on Informa is not relevant now since its latest release.

I am not mincing my words when I say that each API has its own strengths, Informa library is pretty bulky but supports OPML while Rome has a wider support for all kind of XML feeds and has a pluggable architecture. The good thing about these APIs is that they pretty much offer you everything that you may want to do with feeds, reading, generating your own, and creating a digest from multiple feeds and so on.

To run these JSPs, needless to say, you would need to download Informa and ROME libraries. I ran these on jakarta-tomcat-5.0.28 / j2sdk1.4.2_06 and the only dependency I was missing was the JDOM jar that ROME needs.

Concurrent Prograaming Good Reference

Concept and Notations in Concurrent Programming By Andrews and Schneider

Attribute Types

from umn site

Distance Measures

Concept Drift

http://www.bloglines.com/blog/Tilmann?id=6

Concept Drift

http://www.bloglines.com/blog/Tilmann?id=6

On the Business Delegate Pattern

http://www-128.ibm.com/developerworks/java/library/j-ejb1022.html

J2EE pattern langugae

from java.sun.com

What is business logic?

The part of an application program that performs the required data processing of the business. It refers to the routines that perform the data entry, update, query and report processing, and more specifically to the processing that takes place behind the scenes rather than the presentation logic required to display the data on the screen (GUI processing). Client applications are made up of a user interface and business logic. Server applications are mostly business logic.

Both client and server applications also require communications links, but the network infrastructure, like the user interface, is not part of the business logic

Design Patterns: Visual

Berkeley DB: Part Three

Message Handler

package db.GettingStarted;
import com.sleepycat.db.Environment;
import com.sleepycat.db.MessageHandler;

public class MyMessageHandler implements MessageHandler
{
// Our constructor does nothing
public MyMessageHandler() {}
public void message(Environment dbenv, String message)
{
// Put your special message handling code here
}
}

Set the databaseconfig to use this messagehandler
package db.GettingStarted;
import com.sleepycat.db.DatabaseConfig;
...
DatabaseConfig myDbConfig = new DatabaseConfig();
MyMessageHandler mmh = new MyMessageHandler();
myDbConfig.setMessageHandler(mmh);

Chimney Bluff State Park

http://www.fotosearch.com/CRT369/15420-01ns/

Visited this on 06/25/06

Berkeley DB:Part Two

1. Code for exception handing

try
{

}
catch (DatabaseException e)
{
}


2. Errno values, if the errno values are greater than zero then a system error occurred. Special error values like the key and the data being searched is not found results in a error withe negative value.

3. Key and Data of records managed by DatabaseEntry class.

DatabaseConfig class allows setting the properties of the database,
package db.GettingStarted;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.DatabaseType;
import java.io.FileNotFoundException;
...
Database myDatabase = null;
try {
DatabaseConfig dbConfig = new DatabaseConfig();
dbConfig.setAllowCreate(true);
dbConfig.setSortedDuplicates(true);
dbConfig.setType(DatabaseType.BTREE);
myDatabase = new Database("sampleDatabase.db",
null,
dbConfig);

if (myDatabase != null)
myDatabase.close();

} catch (DatabaseException dbe) {
// Exception handling goes here.
} catch (FileNotFoundException fnfe) {
// Exception handling goes here
}

Berkeley DB: Part one

Berkely DB concepts
----------------------

1.DB databases contains records
2. A record contains a key and value.
3. key/data of a record , the data cen be complex.
4. DB database similar like a table in a relation
5. DB applications could use more than one DB databases ( more than 1 tables)
6. The DB database containing records have an assoicated access methods to them
a) Btree
b) Hash
c) Queue
7. Typical DB applications will using many DB databases.
8. Retrieving the records = get()
Putting the records = put()
9. If the databases does not support duplicate records , the next time you insert the data records with existing key, this key replaces the old key.

10. In addition to handles, cursors could be used to insert/retrieve data. Cursors could be used to seek to the data
11. DB provides secondary database which serves as an index to the primary database. Cursors are iterators over the records on the database.
12. Btree access method the most popular method to retrieve data.
13. RecNo , logical records numbers as keys.

Arbitrary Data (strings) Btree or Hash
logical records number (integer) Queue or Recno.

14. Small working datasets no difference between RecNo.

My laptop crash

So what I did not want has finally happened. My laptop crashed yesterday and even though I think I managed to backup some data before that, but now I am in a precarious position.

First I have suse 9.2 and windows on my laptop. And i had a spyware problem with my PC and I tried to remove it with tools in the market. And since I have rebooted nothing shows up on my screen, not even the BIOS screen. I tried to boot from my recovery drive disk in the CD-ROM drive but nothing seems to happen on my computer screen.

I am trying to boot through the SUSE bootable CD and see what happens.

Talk with Werner Vogels and Jim Gray in ACM queue

http://www.acmqueue.com/modules.php?name=Content&pa=showpage&pid=388

Java Caching System

http://java-source.net/open-source/cache-solutions

AWK one liners

Taken from http://www.softpanor....org/Tools/awk.shtml

# Print the length of the longest input line:
awk '{ if (length($0) > max) max = length($0) } END { print max }' data

# Print every line that is longer than 80 characters:
awk 'length($0) > 80' data

# Print the length of the longest line in data:
expand data | awk '{ if (x < length()) x = length() }
END { print "maximum line length is " x }'

# Print seven random numbers from 0 to 100, inclusive:
awk 'BEGIN { for (i = 1; i <= 7; i++) print int(101 * rand()) }

# Print the total number of bytes used by files:
ls -l files | awk '{ x += $5 }
END { print "total bytes: " x }'

# Print the even-numbered lines in the data file:
awk 'NR % 2 == 0' data

# Print first two fields in opposite order:
awk '{ print $2, $1 }' file

# Print lines longer than 72 characters:
awk 'length > 72' file

# Print length of string in 2nd column
awk '{print length($2)}' file

# Add up first column, print sum and average:
{ s += $1 }
END { print "sum is", s, " average is", s/NR }
# Print fields in reverse order:
awk '{ for (i = NF; i > 0; --i) print $i }' file

# Print the last line
awk '{line = $0} END {print line}' file

# Print the total number of lines that contain the word Pat
awk '/Pat/ {nlines = nlines + 1}
END {print nlines}' file

# Print all lines between start/stop pairs:
awk '/start/, /stop/' file

# Print all lines whose first field is different from previous one:
awk '$1 != prev { print; prev = $1 }' file

# Print column 3 if column 1 > column 2:
awk '$1 > $2 {print $3}' file

# Print line if column 3 > column 2:
awk '$3 > $2' file

# Count number of lines where col 3 > col 1
awk '$3 > $1 {print i + "1"; i++}' file

# Print sequence number and then column 1 of file:
awk '{print NR, $1}' file

# Print every line after erasing the 2nd field
awk '{$2 = ""; print}' file

# Print hi 28 times
yes | head -28 | awk '{ print "hi" }'

# Print hi.0010 to hi.0099 (NOTE IRAF USERS!)
yes | head -90 | awk '{printf("hi00%2.0 f \n", NR+9)}'

# Find maximum and minimum values present in column 1
NR == 1 {m=$1 ; p=$1}
$1 >= m {m = $1}
$1 <= p {p = $1}
END { print "Max = " m, " Min = " p }

# Example of using substrings
# substr($2,9,7) picks out characters 9 thru 15 of column 2
{print "imarith", substr($2,1,7) " - " $3, "out."substr($2,5, 3)}
{print "imarith", substr($2,9,7) " - " $3, "out."substr($2,13 ,3)}
{print "imarith", substr($2,17,7) " - " $3, "out."substr($2,21 ,3)}
{print "imarith", substr($2,25,7) " - " $3, "out."substr($2,29 ,3)}

# Single space to Double space
awk '{print ; print ""}' infile > outfile

Data Normalization in Weka

weka.filters.unsupervised.attribute.Normalize

Normalizes all numeric values in the given dataset. The resulting
* values are in [0,1] for the data used to compute the normalization
* intervals.

awk

The command to print the first attribute from a file with attribute values as

attr1, attr2, attr3 ..
is

awk -F, '{print $1}' filename

Web Service, CORBA and RPC

Java EE API's

J2EE architecture

Upper Triangular Matrix

For allocating upper triangular matrix, we use the following technique

(Num) * ( Num -1 ) >> 1 + Num

where num is the number of dimensions of the matrix, what essentially this formulae does is m multiplying ( Num *Num -1 is always divisible by 2 and adding num gives the upper traingular matrix)

Nice trick for allocation of upper triangular matrix.

-Kalyan

Types of Join

Types of join

Occasionally there is a post on a forum asking what a certain type of join is all about, so I thought it would probably be good to have a stock explanation to refer people to so that I don't re-write near enough the same response each time the question arises.

First lets consider these two tables.

A

Key         Data
----------- ----------
1           a      
2           b    

B

Key         Data
----------- ----------
1           c      
3           d         

We can see that the only match is where Key is 1.

INNER JOIN

In an INNER JOIN that will be the only thing returned. If we use the query

SELECT A.[Key] AS aKey, A.Data AS aData, B.[Key] AS bKey, b.Data AS bData
FROM A
INNER JOIN B ON a.[Key] = b.[Key]

the returned set will be

aKey        aData      bKey        bData
----------- ---------- ----------- ----------
1           a          1           c         

In the case of the various outer joins non-matches will be returned also.

LEFT OUTER JOIN

In a LEFT OUTER JOIN everything on the left side will be returned. Any matches on the right side will be returned also, but if there is no match on the right side then nulls are returned instead.

The query

SELECT A.[Key] AS aKey, A.Data AS aData, B.[Key] AS bKey, b.Data AS bData
FROM A
LEFT OUTER JOIN B ON a.[Key] = b.[Key]

returns

aKey        aData      bKey        bData
----------- ---------- ----------- ----------
1           a          1           c      
2           b          NULL        NULL

RIGHT OUTER JOIN

The RIGHT OUTER JOIN is very similar to the LEFT OUTER JOIN, except that, of course, the matching is reversed. Everything on the right side is returned, and only matches on the left side are returned. Any non-matches will be filled with nulls on the left side.

The query

SELECT A.[Key] AS aKey, A.Data AS aData, B.[Key] AS bKey, b.Data AS bData
FROM A
RIGHT OUTER JOIN B ON a.[Key] = b.[Key]

returns

aKey        aData      bKey        bData
----------- ---------- ----------- ----------
1           a          1           c      
NULL        NULL       3           d         

FULL OUTER JOIN

A FULL OUTER JOIN returns a set containing all rows from either side, matched if possible, but nulls put in place if not.

The query

SELECT A.[Key] AS aKey, A.Data AS aData, B.[Key] AS bKey, b.Data AS bData
FROM A
FULL OUTER JOIN B ON a.[Key] = b.[Key]

returns

aKey        aData      bKey        bData
----------- ---------- ----------- ----------
1           a          1           c      
2           b          NULL        NULL
NULL        NULL       3           d         

CROSS JOIN

The CROSS JOIN doesn't obey the same set of rules as the other joins. This is because it doesn't care about matching rows from either side, so there is no ON qualifier within the join clause. This is a simple join that joins all rows on the left side to all rows on the right side. Where the other joins cannot return more rows than exist in the most populous of the source tables, the CROSS JOIN will return the product of rows from each side. If you have 5 rows in Table A, and 6 rows in Table B it will return a set containing 30 rows.

The query

SELECT A.[Key] AS aKey, A.Data AS aData, B.[Key] AS bKey, b.Data AS bData
FROM A
CROSS JOIN B

returns

aKey        aData      bKey        bData
----------- ---------- ----------- ----------
1           a          1           c      
2           b          1           c      
1           a          3           d      
2           b          3           d        

from http://blogs.wdevs.com/colinangusmackay/archive/2006/02/27/12387.aspx

file System Design

SED oneliners

Handy one-liners for SED

HANDY ONE-LINERS FOR SED (Unix stream editor)               Mar. 23, 2001
compiled by Eric Pement                version 5.1
Latest version of this file is usually at:
  http://www.student.northpark.edu/pemente/sed/sed1line.txt
  http://www.cornerstonemag.com/sed/sed1line.txt
This file is also available in Portuguese at:
  http://www.lrv.ufsc.br/wmaker/sed_ptBR.html

FILE SPACING:

# double space a file
sed G

# double space a file which already has blank lines in it. Output file
# should contain no more than one blank line between lines of text.
sed '/^$/d;G'

# triple space a file
sed 'G;G'

# undo double-spacing (assumes even-numbered lines are always blank)
sed 'n;d'

NUMBERING:

# number each line of a file (simple left alignment). Using a tab (see
# note on '\t' at end of file) instead of space will preserve margins.
sed = filename | sed 'N;s/\n/\t/'

# number each line of a file (number on left, right-aligned)
sed = filename | sed 'N; s/^/     /; s/ *\(.\{6,\}\)\n/\1  /'

# number each line of file, but only print numbers if line is not blank
sed '/./=' filename | sed '/./N; s/\n/ /'

# count lines (emulates "wc -l")
sed -n '$='

TEXT CONVERSION AND SUBSTITUTION:

# IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format
sed 's/.$//'               # assumes that all lines end with CR/LF
sed 's/^M$//'              # in bash/tcsh, press Ctrl-V then Ctrl-M
sed 's/\x0D$//'            # gsed 3.02.80, but top script is easier

# IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format
sed "s/$/`echo -e \\\r`/"            # command line under ksh
sed 's/$'"/`echo \\\r`/"             # command line under bash
sed "s/$/`echo \\\r`/"               # command line under zsh
sed 's/$/\r/'                        # gsed 3.02.80

# IN DOS ENVIRONMENT: convert Unix newlines (LF) to DOS format
sed "s/$//"                          # method 1
sed -n p                             # method 2

# IN DOS ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format
# Cannot be done with DOS versions of sed. Use "tr" instead.
tr -d \r outfile            # GNU tr version 1.22 or higher

# delete leading whitespace (spaces, tabs) from front of each line
# aligns all text flush left
sed 's/^[ \t]*//'                    # see note on '\t' at end of file

# delete trailing whitespace (spaces, tabs) from end of each line
sed 's/[ \t]*$//'                    # see note on '\t' at end of file

# delete BOTH leading and trailing whitespace from each line
sed 's/^[ \t]*//;s/[ \t]*$//'

# insert 5 blank spaces at beginning of each line (make page offset)
sed 's/^/     /'

# align all text flush right on a 79-column width
sed -e :a -e 's/^.\{1,78\}$/ &/;ta'  # set at 78 plus 1 space

# center all text in the middle of 79-column width. In method 1,
# spaces at the beginning of the line are significant, and trailing
# spaces are appended at the end of the line. In method 2, spaces at
# the beginning of the line are discarded in centering the line, and
# no trailing spaces appear at the end of lines.
sed  -e :a -e 's/^.\{1,77\}$/ & /;ta'                     # method 1
sed  -e :a -e 's/^.\{1,77\}$/ &/;ta' -e 's/\( *\)\1/\1/'  # method 2

# substitute (find and replace) "foo" with "bar" on each line
sed 's/foo/bar/'             # replaces only 1st instance in a line
sed 's/foo/bar/4'            # replaces only 4th instance in a line
sed 's/foo/bar/g'            # replaces ALL instances in a line
sed 's/\(.*\)foo\(.*foo\)/\1bar\2/' # replace the next-to-last case
sed 's/\(.*\)foo/\1bar/'            # replace only the last case

# substitute "foo" with "bar" ONLY for lines which contain "baz"
sed '/baz/s/foo/bar/g'

# substitute "foo" with "bar" EXCEPT for lines which contain "baz"
sed '/baz/!s/foo/bar/g'

# change "scarlet" or "ruby" or "puce" to "red"
sed 's/scarlet/red/g;s/ruby/red/g;s/puce/red/g'   # most seds
gsed 's/scarlet\|ruby\|puce/red/g'                # GNU sed only

# reverse order of lines (emulates "tac")
# bug/feature in HHsed v1.5 causes blank lines to be deleted
sed '1!G;h;$!d'               # method 1
sed -n '1!G;h;$p'             # method 2

# reverse each character on the line (emulates "rev")
sed '/\n/!G;s/\(.\)\(.*\n\)/&\2\1/;//D;s/.//'

# join pairs of lines side-by-side (like "paste")
sed '$!N;s/\n/ /'

# if a line ends with a backslash, append the next line to it
sed -e :a -e '/\\$/N; s/\\\n//; ta'

# if a line begins with an equal sign, append it to the previous line
# and replace the "=" with a single space
sed -e :a -e '$!N;s/\n=/ /;ta' -e 'P;D'

# add commas to numeric strings, changing "1234567" to "1,234,567"
gsed ':a;s/\B[0-9]\{3\}\>/,&/;ta'                     # GNU sed
sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta'  # other seds

# add commas to numbers with decimal points and minus signs (GNU sed)
gsed ':a;s/\(^\|[^0-9.]\)\([0-9]\+\)\([0-9]\{3\}\)/\1\2,\3/g;ta'

# add a blank line every 5 lines (after lines 5, 10, 15, 20, etc.)
gsed '0~5G'                  # GNU sed only
sed 'n;n;n;n;G;'             # other seds

SELECTIVE PRINTING OF CERTAIN LINES:

# print first 10 lines of file (emulates behavior of "head")
sed 10q

# print first line of file (emulates "head -1")
sed q

# print the last 10 lines of a file (emulates "tail")
sed -e :a -e '$q;N;11,$D;ba'

# print the last 2 lines of a file (emulates "tail -2")
sed '$!N;$!D'

# print the last line of a file (emulates "tail -1")
sed '$!d'                    # method 1
sed -n '$p'                  # method 2

# print only lines which match regular expression (emulates "grep")
sed -n '/regexp/p'           # method 1
sed '/regexp/!d'             # method 2

# print only lines which do NOT match regexp (emulates "grep -v")
sed -n '/regexp/!p'          # method 1, corresponds to above
sed '/regexp/d'              # method 2, simpler syntax

# print the line immediately before a regexp, but not the line
# containing the regexp
sed -n '/regexp/{g;1!p;};h'

# print the line immediately after a regexp, but not the line
# containing the regexp
sed -n '/regexp/{n;p;}'

# print 1 line of context before and after regexp, with line number
# indicating where the regexp occurred (similar to "grep -A1 -B1")
sed -n -e '/regexp/{=;x;1!p;g;$!N;p;D;}' -e h

# grep for AAA and BBB and CCC (in any order)
sed '/AAA/!d; /BBB/!d; /CCC/!d'

# grep for AAA and BBB and CCC (in that order)
sed '/AAA.*BBB.*CCC/!d'

# grep for AAA or BBB or CCC (emulates "egrep")
sed -e '/AAA/b' -e '/BBB/b' -e '/CCC/b' -e d    # most seds
gsed '/AAA\|BBB\|CCC/!d'                        # GNU sed only

# print paragraph if it contains AAA (blank lines separate paragraphs)
# HHsed v1.5 must insert a 'G;' after 'x;' in the next 3 scripts below
sed -e '/./{H;$!d;}' -e 'x;/AAA/!d;'

# print paragraph if it contains AAA and BBB and CCC (in any order)
sed -e '/./{H;$!d;}' -e 'x;/AAA/!d;/BBB/!d;/CCC/!d'

# print paragraph if it contains AAA or BBB or CCC
sed -e '/./{H;$!d;}' -e 'x;/AAA/b' -e '/BBB/b' -e '/CCC/b' -e d
gsed '/./{H;$!d;};x;/AAA\|BBB\|CCC/b;d'         # GNU sed only

# print only lines of 65 characters or longer
sed -n '/^.\{65\}/p'

# print only lines of less than 65 characters
sed -n '/^.\{65\}/!p'        # method 1, corresponds to above
sed '/^.\{65\}/d'            # method 2, simpler syntax

# print section of file from regular expression to end of file
sed -n '/regexp/,$p'

# print section of file based on line numbers (lines 8-12, inclusive)
sed -n '8,12p'               # method 1
sed '8,12!d'                 # method 2

# print line number 52
sed -n '52p'                 # method 1
sed '52!d'                   # method 2
sed '52q;d'                  # method 3, efficient on large files

# beginning at line 3, print every 7th line
gsed -n '3~7p'               # GNU sed only
sed -n '3,${p;n;n;n;n;n;n;}' # other seds

# print section of file between two regular expressions (inclusive)
sed -n '/Iowa/,/Montana/p'             # case sensitive

SELECTIVE DELETION OF CERTAIN LINES:

# print all of file EXCEPT section between 2 regular expressions
sed '/Iowa/,/Montana/d'

# delete duplicate, consecutive lines from a file (emulates "uniq").
# First line in a set of duplicate lines is kept, rest are deleted.
sed '$!N; /^\(.*\)\n\1$/!P; D'

# delete duplicate, nonconsecutive lines from a file. Beware not to
# overflow the buffer size of the hold space, or else use GNU sed.
sed -n 'G; s/\n/&&/; /^\([ -~]*\n\).*\n\1/d; s/\n//; h; P'

# delete the first 10 lines of a file
sed '1,10d'

# delete the last line of a file
sed '$d'

# delete the last 2 lines of a file
sed 'N;$!P;$!D;$d'

# delete the last 10 lines of a file
sed -e :a -e '$d;N;2,10ba' -e 'P;D'   # method 1
sed -n -e :a -e '1,10!{P;N;D;};N;ba'  # method 2

# delete every 8th line
gsed '0~8d'                           # GNU sed only
sed 'n;n;n;n;n;n;n;d;'                # other seds

# delete ALL blank lines from a file (same as "grep '.' ")
sed '/^$/d'                           # method 1
sed '/./!d'                           # method 2

# delete all CONSECUTIVE blank lines from file except the first; also
# deletes all blank lines from top and end of file (emulates "cat -s")
sed '/./,/^$/!d'          # method 1, allows 0 blanks at top, 1 at EOF
sed '/^$/N;/\n$/D'        # method 2, allows 1 blank at top, 0 at EOF

# delete all CONSECUTIVE blank lines from file except the first 2:
sed '/^$/N;/\n$/N;//D'

# delete all leading blank lines at top of file
sed '/./,$!d'

# delete all trailing blank lines at end of file
sed -e :a -e '/^\n*$/{$d;N;ba' -e '}'  # works on all seds
sed -e :a -e '/^\n*$/N;/\n$/ba'        # ditto, except for gsed 3.02*

# delete the last line of each paragraph
sed -n '/^$/{p;h;};/./{x;/./p;}'

SPECIAL APPLICATIONS:

# remove nroff overstrikes (char, backspace) from man pages. The 'echo'
# command may need an -e switch if you use Unix System V or bash shell.
sed "s/.`echo \\\b`//g"    # double quotes required for Unix environment
sed 's/.^H//g'             # in bash/tcsh, press Ctrl-V and then Ctrl-H
sed 's/.\x08//g'           # hex expression for sed v1.5

# get Usenet/e-mail message header
sed '/^$/q'                # deletes everything after first blank line

# get Usenet/e-mail message body
sed '1,/^$/d'              # deletes everything up to first blank line

# get Subject header, but remove initial "Subject: " portion
sed '/^Subject: */!d; s///;q'

# get return address header
sed '/^Reply-To:/q; /^From:/h; /./d;g;q'

# parse out the address proper. Pulls out the e-mail address by itself
# from the 1-line return address header (see preceding script)
sed 's/ *(.*)//; s/>.*//; s/.*[:<] *//'

# add a leading angle bracket and space to each line (quote a message)
sed 's/^/> /'

# delete leading angle bracket & space from each line (unquote a message)
sed 's/^> //'

# remove most HTML tags (accommodates multiple-line tags)
sed -e :a -e 's/<[^>]*>//g;/
# extract multi-part uuencoded binaries, removing extraneous header
# info, so that only the uuencoded portion remains. Files passed to
# sed must be passed in the proper order. Version 1 can be entered
# from the command line; version 2 can be made into an executable
# Unix shell script. (Modified from a script by Rahul Dhesi.)
sed '/^end/,/^begin/d' file1 file2 ... fileX | uudecode   # vers. 1
sed '/^end/,/^begin/d' "$@" | uudecode                    # vers. 2

# zip up each .TXT file individually, deleting the source file and
# setting the name of each .ZIP file to the basename of the .TXT file
# (under DOS: the "dir /b" switch returns bare filenames in all caps).
echo @echo off >zipup.bat
dir /b *.txt | sed "s/^\(.*\)\.TXT/pkzip -mo \1 \1.TXT/" >>zipup.bat

TYPICAL USE: Sed takes one or more editing commands and applies all of
them, in sequence, to each line of input. After all the commands have
been applied to the first input line, that line is output and a second
input line is taken for processing, and the cycle repeats. The
preceding examples assume that input comes from the standard input
device (i.e, the console, normally this will be piped input). One or
more filenames can be appended to the command line if the input does
not come from stdin. Output is sent to stdout (the screen). Thus:

cat filename | sed '10q'        # uses piped input
sed '10q' filename              # same effect, avoids a useless "cat"
sed '10q' filename > newfile    # redirects output to disk

For additional syntax instructions, including the way to apply editing
commands from a disk file instead of the command line, consult "sed &
awk, 2nd Edition," by Dale Dougherty and Arnold Robbins (O'Reilly,
1997; http://www.ora.com), "UNIX Text Processing," by Dale Dougherty
and Tim O'Reilly (Hayden Books, 1987) or the tutorials by Mike Arst
distributed in U-SEDIT2.ZIP (many sites). To fully exploit the power
of sed, one must understand "regular expressions." For this, see
"Mastering Regular Expressions" by Jeffrey Friedl (O'Reilly, 1997).
The manual ("man") pages on Unix systems may be helpful (try "man
sed", "man regexp", or the subsection on regular expressions in "man
ed"), but man pages are notoriously difficult. They are not written to
teach sed use or regexps to first-time users, but as a reference text
for those already acquainted with these tools.

QUOTING SYNTAX: The preceding examples use single quotes ('...')
instead of double quotes ("...") to enclose editing commands, since
sed is typically used on a Unix platform. Single quotes prevent the
Unix shell from intrepreting the dollar sign ($) and backquotes
(`...`), which are expanded by the shell if they are enclosed in
double quotes. Users of the "csh" shell and derivatives will also need
to quote the exclamation mark (!) with the backslash (i.e., \!) to
properly run the examples listed above, even within single quotes.
Versions of sed written for DOS invariably require double quotes
("...") instead of single quotes to enclose editing commands.

USE OF '\t' IN SED SCRIPTS: For clarity in documentation, we have used
the expression '\t' to indicate a tab character (0x09) in the scripts.
However, most versions of sed do not recognize the '\t' abbreviation,
so when typing these scripts from the command line, you should press
the TAB key instead. '\t' is supported as a regular expression
metacharacter in awk, perl, and HHsed, sedmod, and GNU sed v3.02.80.

VERSIONS OF SED: Versions of sed do differ, and some slight syntax
variation is to be expected. In particular, most do not support the
use of labels (:name) or branch instructions (b,t) within editing
commands, except at the end of those commands. We have used the syntax
which will be portable to most users of sed, even though the popular
GNU versions of sed allow a more succinct syntax. When the reader sees
a fairly long command such as this:

  sed -e '/AAA/b' -e '/BBB/b' -e '/CCC/b' -e d

it is heartening to know that GNU sed will let you reduce it to:

  sed '/AAA/b;/BBB/b;/CCC/b;d'      # or even
  sed '/AAA\|BBB\|CCC/b;d'

In addition, remember that while many versions of sed accept a command
like "/one/ s/RE1/RE2/", some do NOT allow "/one/! s/RE1/RE2/", which
contains space before the 's'. Omit the space when typing the command.

OPTIMIZING FOR SPEED: If execution speed needs to be increased (due to
large input files or slow processors or hard disks), substitution will
be executed more quickly if the "find" expression is specified before
giving the "s/.../.../" instruction. Thus:

  sed 's/foo/bar/g' filename         # standard replace command
  sed '/foo/ s/foo/bar/g' filename   # executes more quickly
  sed '/foo/ s//bar/g' filename      # shorthand sed syntax

On line selection or deletion in which you only need to output lines
from the first part of the file, a "quit" command (q) in the script
will drastically reduce processing time for large files. Thus:

  sed -n '45,50p' filename           # print line nos. 45-50 of a file
  sed -n '51q;45,50p' filename       # same, but executes much faster

If you have any additional scripts to contribute or if you find errors
in this document, please send e-mail to the compiler. Indicate the
version of sed you used, the operating system it was compiled for, and
the nature of the problem. Various scripts in this file were written
or contributed by:

Al Aab    # "seders" list moderator
Edgar Allen               # various
Yiorgos Adamopoulos 
Dale Dougherty      # author of "sed & awk"
Carlos Duarte     # author of "do it with sed"
Eric Pement     # author of this document
Ken Pizzini           # author of GNU sed v3.02
S.G. Ravenhall  # great de-html script
Greg Ubben       # many contributions & much help

tpl@eng.cam.ac.uk

Elevator Design Problem

UML By Examples

Home UML Resources Table of Contents 1 Elevator Problem 2 Unified Modeling Language 3 Analysis 3.1 Use Case Dagram 3.2 Class Diagram 3.3 State Diagram 4 Design 4.1 Sequence Diagram 4.2 Collaboration Diagram 5 Detail Design 5.1 Detail Class Diagram 5.2 Detail Opreation Description 5.3 Pseud-Code 6. Acknowledgement 0. Introduction The aim of this tutorial is to show how to use UML in "real" software development environment. 1. Elevator Problem A product is to be installed to control elevators in a building with m floors. The problem concerns the logic required to move elevators between floors according to the following constraints: Each elevator has a set of m buttons, one for each floor. These illuminate when pressed and cause the elevator to visit the corresponding floor. The illumination is canceled when the elevator visits the corresponding floor. Each floor, except the first floor and top floor has two buttons, one to request and up-elevator and one to request a down-elevator. These buttons illuminate when pressed. The illumination is canceled when an elevator visits the floor and then moves in the desired direction. When an elevator has no requests, it remains at its current floor with its doors closed. 2. Unified Modeling Language UML is a modeling language that only specifies semantics and notation but no process is currently defined. Thus, we decided to do the analysis as follows; Use Case Diagram Class Diagram Sequence Diagram Collabration Diagram State Diagram 3. Analysis 3.1. Use case diagram Use case description: A generalized description of how a system will be used. Provides an overview of the intended functionality of the system. Understandable by laymen as well as professionals. Use Case Diagram: Elevator basic scenario that can be extracted from Use Case Diagram: Passenger pressed floor button Elevator system detects floor button pressed Elevator moves to the floor Elevator doors open Passenger gets in and presses elevator button Elevator doors closes Elevator moves to required floor Elevator doors open Passenger gets out Elevator doors closes 3.2. Class Diagram Class diagrams show the static structure of the object, their internal structure, and their relationships. Class diagram: 3.3. State diagram A state diagram shows the sequences of states an object goes through during it's life cycle in response to stimuli, together with its responses and actions. 4. Design The design phase should produce the detailed class diagrams, collaboration diagrams, sequence diagrams, state diagrams, and activity diagram. However, the elevator problem is too simple for an activity diagram. Thus, we are not using an activity diagram for the elevator problem. 4.1. Sequence Diagram A sequence diagram and collaboration diagram conveys similar information but expressed in different ways. A Sequence diagram shows the explicit sequence of messages suitable for modeling a real-time system, whereas a collobration diagram shows the relationships between objects. Sequence Diagrams: Sequence Diagram for Serving Elevator Button Sequence Diagram for Serving Door Button 4.2. Collaboration diagram Describes the set of interactions between classes or types Shows the relationships among objects Collabration diagrams: Collabration Digaram for Serving Elevator Button Collabration Digaram for Serving Door Button 5. Detail Design 5.1. Detail Class Diagram 5.2. Detail Operation Description Module Name Elevator_Control::Elevator_control_loop Module Type Method Input Argument None Output Argument None Error Message None File Access None File Change None Method Invoke button::illuminate, button::cancel_illumination, door::open, door::close, elevator::move, elevator::stop Narative 5.3. Pseudo-Code void elevator_control (void) { while a button has been pressed if button not on { button::illuminate; update request list; } else if elevator is moving up { if there is no request to stop at floor f Elevator::move one floor up; else } 6. Acknowledgement This example was developed for topic in software engineering in Vanderbilt University by myself and my best friends: Helen Xioa Valeria Amburge Parvathi RajaGopal

What is Windows Collation

Windows collations define rules for storing character data based on an associated Windows locale.

Semaphore and Mutex

What's the difference between semaphore and mutex?

A: Rules of thumb:

- By semaphore we actually mean counting semaphore. By mutex we actually mean mutex semaphore. A mutex is essentially a binary semaphore. You can replace any Mutex with a Semaphore of MaxCount 1.

- Mutexes are usually more efficient than binary semaphores.

- Mutex has an owner concept: unlocking a mutex can be only done by the thread that locked (or, equivalently, "owns") the mutex.

- However, though I don't think it's a real issue in this particular case either, mutex can do fancy things with the thread that has locked the mutex (mutex owner thread), like raising its priority to the highest one of the threads waiting for the mutex to prevent so called priority inversion. (huican ping notion, not in the original version)