A Programmer's Day

What makes Android Programming Simpler and iOS difficult?

2011-11-11T09:49:00.001+05:00

I cannot start writing iPhone and iPad software because?

I don't have an Apple... No! don't bring me a KG of fresh red apples please, I am referring to the Apple which is a computer. It's impossible to code stuff up without an Apple machine, even for sake of learning. Apple MUST create a tool chain for people running Windows as we know it's the most widely used operating system, just like the iPhone which is a crazily used "Somewhat Smart" Phone. They could create a development environment, and a few emulators to get new going with iOS development. I believe it would cost less than $100k to develop such a solution, maintenance cost won't go beyond this as well.

I can start writing Android software because?

Because the tool chain is available for Windows, and Linux as well. We got things like Eclipse and ADT, that make producing Android software very easy. Anybody and everybody with little knowledge and some enthusiasm can jump into it.

For fresh grads, Android is easy but iOS is difficult because?

Fresh grads are usually scared of new programming languages, basically the PHD and MPhild wielding "theoretical giants" that are dominating the universities cultivate the fear. They are the people(almost always) not good at programming, but super fast at publishing papers and attempting exams; and that is precisely why they can't find jobs in practical code writing/analysis/management positions in industry and seek refuge(read occupy) universities. These people scare the youth away from real life programming, by over-explanation of simple constructs like if/for/while.
Objective C is certainly not the most popular academic language, Java on the other hand is being taught in thousands of Universities around the world. C is usually the first programming language and Java comes afterwards, but there are cases when they take directly off from Java.
The point is, adopting to Android platform's Java based program writing is very easy for fresh grads on the other hand Objective-C centric iOS programming is relatively difficult to adapt.

Solutions for developing iPhone apps without a Mac are available but the seem to even complicate the process. We got options like "WebView", JavaScript and HTML 5 based widgets or applications that can run on any mobile platform (Android, iOS, WP7). But if you want to leverage the platform specific benefits, again you must mess with Obective-C or Java.

I deliberately left Windows Phone 7 or 7.5 because this debate is not concerned with Microsoft's lagging smart phone platform. Microsoft VB.Net, C# .Net are being taught in a very little amount of universities, although people learn these languages once they complete graduation. But still Microsoft is far behind from Apple and Google in Smart Phone computing and these two are the real competitors for the throne of Mobile/Tablet computing.

Microsoft's like a mammoth right now, it's got a lot of software(Desktop/Server OS, CMS, Databases, Application Framework etc.) in its repertoire, a huge and stable customer base, but still it's unable to produce a truly strong iOS/Android rival. HTC is supposed to offer a smart phone with Quad Core Nvidia Tegra 3 processor by the end of this year or earlier next year, but Windows Phone will not get even a dual core processor by late 2012.
Blackberry is another platform Java coders can head to, but the BB show seems to be coming to an end. And most probably they'll shelve their OS (BB OS7) and cancel QNX program, and move to Windows Phone joining the club Nokia earlier this year joined.

C# string utility functions containsAtLeastOneChar-containsOnlySpecifiedSpecChars-excludesSimilar

2011-10-07T19:26:00.000+05:00

A utility class to perform simple operations on strings using C#. The logic is simple, one can transform the code given below to C++, PHP, or JavaScript within 2 minutes. I know each one of the programming languages I mentioned here, and all other first class modern programming languages have got sophisticated regular expression packages. But, the use of regex is not an option for everyone. Some got the skill to learn, but just don't have the time needed to read docs. Some don't want to import in a full blown namespace like System.Text.RegularExpressions
And some other are plain lazy.
Here goes the code, the names are descriptive enough, first one containsAtLeastOneChar checks whether a string contains at least one character of a certain character set. For example, we want to check whether a password generated by a automatic password generator contains at least one capital letter, one number, and one special character.
Second one, containsOnlySpecifiedSpecChars returns true when the supplied string conains only specified characters.
Third function excludesSimilar will return true when a string does not contain repeating characters.
The class Commons contains static member variables, you could try passing these values to the static member functions of this class and experiment around to check the results. It will also save you some typing :)
You could just copy paste the code given below as it is, it's supposed to work.
Happy coding!

public class Commons
{
public static bool containsAtLeastOneChar(string strWord, string strCompairTo)
{
int nIdx = -1;
foreach (char c in strWord)
{
nIdx = strCompairTo.IndexOf(c);
if (nIdx >= 0) return true;
}
return false;
}
public static bool containsOnlySpecifiedSpecChars(string strWord, string strSpecialChars)
{
foreach (char c in strWord)
{
if ((strCaps.IndexOf(c) < 0) & (strSmalls.IndexOf(c) < 0) & (strNums.IndexOf(c) < 0))
{
if (strSpecialChars.IndexOf(c) < 0)
return false;
}
}
return true;
}
public static bool excludesSimilar(string strWord)
{
foreach (char c in strWord)
{
if (strWord.IndexOf(c) != strWord.LastIndexOf(c))
return false;
}
return true;
}

public static string strCaps = "ABCDEFGHIKLMNOPQRSTUVWXYZ";
public static string strSmalls = "abcdefghijklmnopqrstuvwxyz";
public static string strNums = "0123456789";
}//class

Reverse of a string by words C# example

2011-09-04T23:24:00.000+05:00

Reverse of a string in C#, VB .Net, or C++ is pretty easy. Please not that we are talking about a word by word reversal, like

Hello How Are You
Becomes
You Are How Hello

Reversing characters inside a word is a different story.
Some people find it difficult, so I'm putting the C# example code here.

class Program
{
public static string reverseIt(string strSource)
{
string[] arySource = strSource.Split(new char[] { ' ' });
string strReverse = string.Empty;
for (int i = arySource.Length - 1; i >= 0; i--)
{
strReverse = strReverse + " " + arySource[i];
}
Console.WriteLine("Original: " + strSource);
Console.WriteLine("Reverse: " + strReverse);

return strReverse;
}

static void Main(string[] args)
{
reverseIt("Hello World! Let's Reverse The String");
}
}

The algorithm is very simple and it's made easy with constructs provided by .Net framework.

Assumption:

We assume that two words inside a given string will be separated by one white space.

First of all we call Split method on the string which user provided us, we pass in an array of characters which contains only one space, although we can put other characters like tab '\t' as separator in here. The method call

string[] arySource = strSource.Split(new char[] { ' ' });

When separated, the array arySource will look like as given below

Array Index	Word
0	Hello
1	World
2	Let's
3	Reverse
4	The
5	String

Now we put a for loop, and start iterating from the end of array to beginning of array. The loop will start working from arySource.Length - 1 i.e. 5 in our case and it will keep on moving until value of variable i reaches -1.
In every iteration of loop, we pick a word a and put to the strReverse. The string will be built in a triangle form as given below

Please feel free to comment and ask any further questions.

Using nested conditional statements as a replacement to switch case statement in C#, C++, Java, PHP, JavaScript

2011-08-04T02:23:00.000+05:00

Switch statements are nice, sometimes we need to just return some value based on an input variable. For example in our case I needed to get the key field of an LDAP object class we preferred to use in our software. So I had a simple C# function which went something like this

public static string getKeyByObjectClass(string strObjectClass){
switch(strObjectClass){
case "user":
return "samAccountName";
case "user-mailbox":
return "samAccountName";
case "user-mail":
return "samAccountName";
case "contact":
return "CN";
case "contact-mail":
return "CN";
case "group":
return "samAccountName";
default:
return "";
}
}

I thought it is possible to simplify this switch statement with a nested conditional statement. And following was the result of some deliberation ;)

public static string getKeyByObjectClass(string strObjectClass){
return (strObjectClass == "user") ? "samAccountName" : (strObjectClass == "user-mailbox") ?"samAccountName" :(strObjectClass == "user-mail") ? "samAccountName" : (strObjectClass == "contact") ? "CN" :(strObjectClass == "contact-mail") ? "CN" : (strObjectClass == "group") ? "samAccountName" : "";

You can definitely use || operator, minimize the code, and refine the crude version of nested conditional statement we created earlier, let's just do that

public static string getKeyByObjectClass(string strObjectClass){
return (strObjectClass == "user" || strObjectClass == "user-mailbox" || strObjectClass == "user-mail") ? "samAccountName" : (strObjectClass == "contact" || strObjectClass == "contact-mail" ) ? "CN" : "";
}

But now we definitely have some compromise on flexibility, maybe we'll want to use a different key for an object class say "user-mail" and then we'll have to modify this code in tiny bit different way(maintenance hell anyone?) ;)

I'm sure many intelligent folks have already done this or even a better variation but I also know that there are dumb guys and gals just like me out there who would most probably yell "Eurika!!!" on understanding the magic of nested conditional statements.

Its not just and only C# stuff, in fact the code will work with JavaScript, PHP, Java, C++ and many others with little or no variation.

Cannot rename htaccess.txt to .htaccess in cPanel File Manager

2011-07-30T06:09:00.000+05:00

Just today I was trying to fix the 404 broken link problem with the Joomla installation on my upcoming website, http://www.ldapfilters.com which will contain certain knowledge base about LDAP and directory servers in general, along with discussion forums.
So, they say WARNING! Apache users only! Rename htaccess.txt file to .htaccess before activating.
I opened the File Manager from CPanel, scrolled down to the htaccess.txt file right clicked and renamed it and the File Manager finally said "No! You can't rename, a file already exists." I tried and retried several gimmicks but it didn't work.
Solution: Then I decided to try legacy file explorer, I opened the CPanel Legacy File Manager, located htaccess.txt, clicked it, selected Rename from the menu, typed in .htaccess and it worked well ;)

A Confusion: I got confused and start thinking, shall I rename htaccess.txt to htaccess.htaccess or just remove the .txt from end of file name, and put a dot at the start of file name? Well the answer is yes, I had to take the second option. Therefore, just rename it to .htaccess that means a file with no name but just an extension.
And one more thing, I renamed htaccess.txt to htaccess_.txt and then tried to access my website, even the home page of my Joomla based website didn't show up let alone the broken links which I was trying to fix :p
Therefore, be very careful when you touch these configuration files, they are absolutely sensitive. Some times you catch the bug right after saving that file and refreshing that page but at some other time the setting you've just changed has got a much deeper effect which gets unleashed by some twisted user action sequence, so here's the GOLDEN ADVICE

Back those files up!!!

System.DirectoryServices A referral was returned from the server Exception

2011-03-07T21:39:00.001+05:00

System.DirectoryServices showed " A referral was returned from the server " Exception just today, and it left me wondering what's wrong?
I was trying to pull data from a Microsoft Active Directory Group, and while attempting to query the data following exception was occurring. An eagle eye debugging showed the cause and it was simple but stupid.
You know following is the format of LDAP connection string
LDAP://abc.xyz.pqr.lab:389/CN=TheGroup,CN=Users,DC=abc,DC=xyz,DC=pqr,DC=lab

But our dear programmer had done it a little differently, I think it was just a type, the wrong format of LDAP connection string was following
LDAP://abc.xyz.pqr.lab/CN=TheGroup,CN=Users,DC=abc,DC=xyz,DC=pqr,DC=lab:389

And this was causing the system to show the Active Directory related exception in C# .Net on Visual Studio 2008.

Using Excel 2003 File As Data Source Of Visual Studio .Net Data Driven Unit or Functional Test

2011-02-18T04:30:00.000+05:00

First of all this will be the attribute tag for setting up data access of a data driven Unit or Function test in Visual Studio, I am using Visual Studio 2008 but I think same will work in Visual Studio 2010

[DataSource("System.Data.OleDb", "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\\FunctionalTestsDataFiles\\Smoke_Cred.xls;Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=1\";", "ldapdest$", DataAccessMethod.Sequential), TestMethod]

Put the name of your .xls file in place of "Smoke_Cred.xls" and put the name of your excel sheet in place of "ldapdest$", don't forget to put the $ sign after the name of your Excel sheet.

Be very careful with the "System.Data.OleDb" because the people at Microsoft have made a case sensitive comparison in their code which wasted so many of my hours, and gave me too much tension.

If you write "System.Data.OleDB" instead, it will fail in functional/unit test but it will work fine in other connection string testing utilities.

Second thing, the syntax of spread sheets inside excel files is different from syntax used for Access databases. You need to put a $ character after the name of the sheet you are trying to access.

I found an article on MSDN about running data driven test cases with Ms Access, but there was no mention of these little pieces of shit which I am sure must have been killing time of many poor developers.

Instead of solving problems, you have to run after crappy case sensitive and idiotic connection strings, what an irony!!!

If you use "System.Data.OleDB" mistakenly, following error will be displayed

Error details: Unable to find the requested .Net Framework Data Provider. It may not be installed.

And if you somehow luckily fix this, and don't know that you need to put a $ sign after the name of that God damn excel sheet, you'll get following error

Error details: The Microsoft Jet database engine could not find the object 'ldapdest'. Make sure the object exists and that you spell its name and the path name correctly.

One more twist, the TestContext used by some s of b in MSDN article is not found anywhere by default, and you need to define it before using it. I wonder what Microsoft's trying to do with us developers.

private TestContext testContextInstance;

public TestContext TestContext
{
get { return testContextInstance; }
set { testContextInstance = value; }
}

The link of the piece of crap MSDN article is following:

http://msdn.microsoft.com/en-us/library/ms182527.aspx

I know I'm using rash and bad language but what else do you expect from someone on 4:30 AM? When you come to know that only problem with your code was that you used "B" instead of "b" and you must be intelligent enough to put a $ in the end of table name of excel sheets here. I mean why in the world Microsoft idiots cant just fix these tiny issues??? I'm too much pissed right now... literally pissed...

Turn On or Off A Windows Computer's Display With SendMessage User32.dll Win32API Call In C++ or C#

2011-01-22T12:56:00.000+05:00

How Can I Turn Off My Laptop's Display Whenever I Want?

Update: I have moved the .exe download from 4Shared to my own domain (http://www.ldapfilters.com), therefore the download is a one step process now.
I recently felt the need to turn off my laptop's monitor on my will, but you know there ain't such a button on almost all laptops. (Not interested in tech stuff? scroll down directly to Download, and get the executeable) So I tried to search around the internet for some utility, sadly speaking I didn't find any such thing. But you know I'm a programmer after all, therefore instead of searching a trust-worthy utility, I sought a do it yourself code example. I found the example here on code project:http://www.codeproject.com/KB/system/display_states.aspxThe code needed to turn your monitor off/on is literally a one liner. All you need is one line, and your monitor will be powered off as soon as you run the .exe file. Here's the code friends:
#include <Windows.h>
int main(int argc, char* argv[]){
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) 2);// this c++ code will turn the monitor off
return 0;
}

You will be wondering, how the monitor/display will be turned back on? The good news is Windows handles that part automatically. Whenever we turn off display with this cut throat application of ours, moving mouse or pressing a key will bring the monitor back to life. Although broadcasting another message will fire the display up, but we don't need that I think. Still, here's the code:SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) 1);Take this piece of code to any C++ IDE of your choice(of course Windows duffer!!!), just compile build and your very own application to turn off the monitor will be ready.Place the executable anywhere you want, create a shortcut on desktop, whenever you'll click it the monitor will go dark.And if you don't wanna do that, just download the ready to run executable of this cut throat advanced bleeding edge top class wonderful awesome @#%$#%&~!^&%$#@+ app that can shut down your PC or Laptop's display/monitor whenever you want here !!!

Download

Instructions:

Just place the .exe file anywhere in your system, double clicking it will turn off the monitor you may create a shortcut on desktop, or pin it to task bar for easy access (details below).
Moving the mouse, or pressing a key on keyboard will turn your system's display back on.

Please keep that in mind:

This utility does not open any network communications port
This utility does not read/write any kind of files to/from your computer's hard disk
This utility does not read/write anything to/from Windows Registry.

Therefore, if the file you download tries to do any of the above, the file is not original and someone has tampered with it.Making Things Even Better (Value Addition):There's a very cool Windows 7 feature which I've used to make things even better on my laptop.The feature goes like you can access the shortcuts pinned to Windows by pressing Windows Button + a number. The leftmost minimized program or pinned shortcut will be activated by pressing Windows + 1, second left with Windows + 2, so on and so forth. For example see the snap shot of my current Windows Toolbar

The yellow numbers aren't found originally in the interface, I've annotated the snap shot on purpose. Right now, if I will press Windows Key and then press 2 key(not from num-pad) the Windows Media player which is second from left will be maximized. Similarly, Windows 5 will cause Google Chrome to open up. Windows 8 will maximize Ms Paint. I have pinned the .exe file of our cut throat power off display application to Task bar. Therefore, if I will press Windows key + 1 display of my laptop will be turned off.Technical Explanation:How Windows WorksBasically we need to understand the architecture of Windows applications to get the core of what's happening in this single line of code.In a Windows environment, we don't interact with any application directly. Instead whenever we perform an action we are talking to Windows Operating System, the OS takes our command/action and passes it over to an application depending on the location of the action/command/event. For Example:Like if you click in a Ms Word window, following will happen:

Windows OS will catch the message
It will see that currently the window associated with Ms Word was active
It will pass over your command in form of a message to Ms Word
Each and every Windows based application contains a "Windows Message Message Pump" loop, which keeps watching for incoming messages from Windows OS
In this case, the message pump inside Ms Word will catch the message that "user clicked somewhere".
Then Ms Word will handle the message what ever way it wants to.
If an application has not handled a certain message, the message will simply have no affect on its health and the application will just discard the message.

People writing code for .Net platform (usually) don't know these things, but that's the basic Ms Windows architecture, and its not going anywhere any time soon. The "Windows Message Pump" plus WndProc method is alway in there.Where does SendMessage() fit in?SendMessage is found in User32.dll, and its a Win32 API call(scary bare bone stuff for .Netters).In this program we are broadcasting a message, which is not intended for any specific application. Like the fishermen broadcast help requests on radio. We are just saying "Hey anybody out there, I am sending a WM_SYSCOMMAND which is related to SC_MONITORPOWER with a value of 2". Luckily there is a portion of Windows which is handling this message, its the same part which turns your display off after a certain amount of time.This function call won't affect anything else on your system, cause no other application is consuming this message.So, in the end, your display is powered off so that you can sit back and relax ;)

You might have noticed that I just provided C++ source code, and there ain't not C# .Net code as sample. I think its quite easy to setup p/Invoke calls these days, I am intentionally avoiding the topic as I want to keep the article short and to the point. Just if you've understood the scheme of things, you can easily setup a C#.Net or VB.Net version.

DISCLAIMER: There is no guarantee or warantee that this program will work as specified in this post. Author will not be responsible for any damage due to use of instructions provided in this post.

sizeof operator on a double array in c++

2010-09-26T15:55:00.000+05:00

Char** Array of Strings in C and C Plus Plus(C++)

2010-09-25T22:18:00.000+05:00

Defining strings in C and C++:
Basically, a string is an array of characters (char) data type variables. And it is defined as following:

char myString[50];

It is possible to initialize the array of characters at run time

char myInitializedString[50]={"I am invincible..."};
An alternate technique of defining character arrays with the help of char pointers can be used as well, which is demonstrated below:
char* myInitializedCharPtr = "Here we go again";

Multi dimensional arrays in c and c++:
What if someone wants to store multiple strings... in an array... array of strings in other words... well... its fairly simple to create an initialized array of strings

char ArrayOfStringsInitialized[3][50] = {"Rock and Rolla","iToka","Thats it"};
This array of strings contains 3 strings, each of length upto 50 characters.
To iterate the array we just created, do the following...

for(int n = 0; n<=2/*less than last element of array*/;n++)
{
cout<<ArrayOfStringsInitialized[n]<<endl;
}
For two dimensional array defined with this technique, the programmers don't need to free the memory explicitly.
Dynamic two dimensional arrays

Suppose we need to create a multi-dimensional array on run time, using pointers... We will need a char double pointer or char**, and it will make the code look something like this

char** greenLandMD;

greenLandMD = new char*[5];// initialize the double pointer 
greenLandMD[0]=new char[4];// initialize 1st char*, with capacity of 4 chars
greenLandMD[1]=new char[5];// initialize 2nd char*, with capacity of 5 chars
    
strcpy(greenLandMD[0],"Bst @");//copy some data to 1st string
strcpy(greenLandMD[1],"Bi! 1");//copy some data to 2nd string
greenLandMD[3]="W ared";// an alternate way of copying data
 
 // print and see the data
cout<<greenLandMD[0]<<endl<<greenLandMD[1]<<endl<<greenLandMD[3]<<endl;

Console will show

c:\>Bst @
Bi! 1
W ared

An alternate way to achieve the same result is given below

cout<<*(greenLandMD+0)<<endl;
cout<<*(greenLandMD+1)<<endl;
cout<<*(greenLandMD+3)<<endl;

At this point, the array will look something like this

There are two things to notice in this image
1- The size of strings contained by array of strings varies.
2- It is possible to leave un-initialized space at any slot of a multi dimensional array in c/c++.
It is a programmer's responsibility to free the memory acquired using this technique, missing such things create memory leaks which cause performance decrease, security related problems, and an all out crash some times.
Freeing memory of char * and char**
Deleting the main array will suffice to free the memory consumed by double pointers. In our case, we'll do following:
delete [] greenLandMD;

I think this much is enough on this topic, for more please feel free to comment this post.

Path to Microsoft Certification for programmers

2010-01-15T14:35:00.000+05:00

In university days I once tried to follow path to Sun Java Certified Programmer. On their web site I found very nice flow charts. For Microsoft's certification I could not find anything of this sort therefore I decided to collect data from Microsoft's web and create my own Microsoft Certification Tree diagram.
Everything seems to be starting from Exam 70-536: TS: Microsoft .Net Framework, Application Development Foundation. We will get MCTS after passing two exams, and MCPD after passing third exam of next stage.

Update: Everything still starts from Exam 70-536.

std::ostringstream AKA String Streams...

2009-06-09T15:02:00.000+06:00

Want to share a few bits about a very important and useful feature of standard library today. std::ostringstream can come in handy in many situation. You know we often need to concatenate strings. And often it becomes tedious, usually this is done using strcat funtion in C and + operator in C++ std::string class . For example

// C style
char * szFullName = strcat("First Name ", " Last Name");

//C++ style
std::string strFirstName = "First Name";
std::string strLastName = "Last Name";
std::string strFullName = strFirstName + " " + strLastName;

std::ostringstream gives us a convenient way to build strings conveniently.
std::ostringstream provides functionality very much similar to sprintf function of C language.

Like for example you got names, ages, and heights of a few kids stored in arrays and you want them to be printed nicely on screen. Perhaps you could use a std::string and + operator to join string but I think using ostringstream will be a better approach.

const int CONST_ARRAY_SIZE = 3;
std::string aryStrNames[CONST_ARRAY_SIZE] = {"Ali", "Jason", "Shiv"};
int aryNAges[CONST_ARRAY_SIZE] = {5,9,11};
float aryFHeight[CONST_ARRAY_SIZE]={3.2,4.0,4.4};
std::ostringstream outBuffer;
for(int i = 0; i < CONST_ARRAY_SIZE; i++){
outBuffer<<aryStrNames[i]<" is " << aryNAges[i] << " years old, and his height is "<< aryFHeight[i] << endl;
}// end for i
cout<< outBuffer.str();

Here's a link to ostringstream on C Plus Plus
http://www.cplusplus.com/reference/iostream/ostringstream/

Working with std::string::substring() method

2009-03-17T21:53:00.001+05:00

Though it is a very simple function, but sometimes people(me too) make a mistake when coding thing up. For example we have a std::string strHello

int nPositoinOfSemiColon = strHello.find(";", 0);

find method will find the fist parameter ";" in strHello, starting from second parameter i.e. 0.
Now the nPositoinOfSemiColon will contain either string::npos which means the string provided to find method was not found in strHello. Or in our case, 5 which is the location of ";".

strHello.substr(0, nPositoinOfSemiColon );

will return "Hello", i.e. 5 characters starting from location 0 in strHello.
Now consider

int nPositionOfSecondSemiColon = strHello.find(";", nPositionOfSemiColon);

Well... writing following line of code will... wonder what...

strHello.substr(nPositionOfSemiColon, nPositionOfSecondSemiColon);

CAUSE AN ERROR!!! FOLKS!!! ERR GRR ERROOORRR... a vicious cruel ugly error... heh heh heh...
Poor baby programmers will asK "But why Uncle why???"
Because, of the values in variables at this time are...

nPositionOfSemiColon = 5
AND
nPositionOfSecondSemiColon = 11
That means
strHello.substr(5, 11);

i.e. extract 11 characters starting from location 5 in strHello.
Whereas, 11 is total length of strHello...

The right way to go is

strHello.substr(nPositionOfSemiColon,
nPositionOfSecondSemiColon - nPositionOfSemiColon);

That means
strHello.substr(5, 6); // That means ";WORLD"

Cheers folks... have fun... remember... coding is a noble pursuit... so just keep hitting it hard... savor the wonders and joys of turning real world into programming language codes, and bear the tensions with enough tolerance...

More C/C++ Interview Questions

2009-03-17T21:50:00.001+05:00

I was keeping this post on hold for almost a month, so that I will post the questions along with the answers... but due to some reasons, I was unable to post the answers...
Will do it some time later in future...
For the time being, the C/C++ interview questions are given below...
If anybody finds out an answer, feel free to write it in comments...

1. What is the difference between a pointer and array?
2. Is it possible to find out the size of an array?
3. What is NULL?
4. How can we find if a pointer contains a valid value or not?
5. We have a circular linked list, and its tail -> next is not pointing to List -> Head. How can we diagnose such an error condition?

A tricky error, when using std::string with *printf funtions

2009-03-09T23:02:00.000+05:00

All of us know what this code (listing 1)will do...

char * szName = "Ex";
printf("%s", szName );

Will anybody tell what will be the result of these lines(listing 2)...

std::string strName = "Zed";
printf("%s", strName);

Ladies and gentlemen... listing two will cause your program to crash. This is a very common mistake made by programming newbies... though an experienced pro may also do the same...

The right way to print the string is

std::string strName = "Zed";
printf("%s", strName.c_str());

such errors are very difficult to spot... Because when reading the code, one often unconsciously considers these lines are correct...

Now people will ask that why in the world will someone create such a ridiculous blend of C and C++... The answer is... I don't know why... But anybody is absolutely free to mix the two compatible languages into a cocktail... I myself did this... when I was new into the dark realm of C/C++ programming... I had my own reasons... others will have their own...

note: *printf means any of the following funtion calls {printf, sprintf, fprintf}

Relevance of C/C++ in today's computing

2009-03-04T23:25:00.000+05:00

A question mostly asked by fresh graduates is "C/C++ are still being used"? The answer is "Yes of course", C/C++ are still being widely used. Many open source projects are done using C/C++. Modern computing scene would be very different if C/C++ were not there... For example

1. Asterisk the open source PBX is written using plain old C language.
2. Maya, a top notch 3D animation suite is written using C++.
3. Postgres, leading open source DBMS which competes to Oracle is done using C.

C is considered the language of choice for writing Operating Systems. All Linux based operating systems are written using C. Microsoft Windows is written using C/C++. They (folks @ Redmond) tried to write Windows Vista using C#, but failed miserably.
C is known as "Mother of all programming languages". C/C++ are primarily used to write mission critical software, when we need high speed and smaller memory foot prints.
I agree that we are living in an internet age, languages lis PHP/ASP.Net/Ruby on Rails are everywhere these days. But does anybody think, what is the engine powering these languages? The web-server which executes PHP code, the browser which displays CSS/HTML and dances around with AJAX, Adobe's Flash things, and many more are all done using C/C++.
Sometimes I think, I will do a detailed workshop titled "The Real Power of C/C++". I'm pretty ambitious in this regards, and I'll surely tell the world about "the happening"...

Calling a web-method from a hyperlink

2009-02-19T12:33:00.000+05:00

I've observed this trend in tech-industry, we will find many articles on difficult topics but its very difficult to find answers to simple questions.
I once faced such a question and figured it out after some experimenting.
The question is how to call a web method (a method exposed by a web service) from a plain HTML web page??? In other words how to call webmethods directly??? Well, folks its really simple to call a web-method from a hyperlink... The HTML goes like this...

<html>
<body>
<p>
<a href = "http://localhost/abcGateway/xgateway.asmx/dostartRecording?recchannel=19">
Start Recording
</a>
</p>
</body>
</html>

Where I have a web-service whose main page is xgateway.asmx, and it exposes a web method "dostartRecording", this web-method takes a parameter "recchannel".
Hi ho now you can enjoy calling a web method directly from your web page.

Difference between Framework and API

2009-02-19T12:27:00.001+05:00

Software Framework: Is a re-usable design for a software system (or subsystem). A software framework may include programs, code libraries, a scripting language, other software to help develop and glue together the different components of a software project. Various parts of the framework maybe exposed through an API.
Microsoft's .Net framework is a very good example of a software framework. It contains compilers, class libraries, an IDE(Visual Studio), and a runtime. Another example is OpenCog: A Software Framework for Integrative Artificial General Intelligence.

API (Application Programming Interface): Is a set of routines( AKA methods, functions), data structures, object classes, and/or protocols provided by libraries and/or operating system services in order to support the building of applications.
An example is Microsoft TAPI(Telephony API), or MySQL connectivity API, or Google MAPS API.

In Microsoft's .Net Framework, only the Base Class Library or BCL are the API. The framework is a bigger thing. API is a part, framework is a whole. Although, API can exist on its own, without a framework as well.

A friend was telling me yesterday "I interviewed someone, he had no idea about difference between Framework and an API". I replied"Owwww that's dumb". In fact, had no idea about the difference either... :p. Well, I think this much is enough to illustrate the difference between Software Framework and API, or Software Framework vs API. ;)

Another example pictured below is the Google's Android Mobile Platform,

You see this platform contains many things, a kernel for low level tasks, certain libraries for OS level chores, Delvik Virtual Machine (an enriched clone of Java Virtual Machine), and the "Application Framework" on on the "third story". Any software we write for Android smart phones will reside on 4th floor, which is labelled "Applications" here.

Working with a std::vector inside an std::map

2009-02-18T19:17:00.000+05:00

Suppose we have a map which contains std::string keys and std::vector values, it will be defined as following

std::map<std::string,std::vector> map_str_vector;

I was doing something like this:

std::vector vec_active_channels;

vec_active_channels.push_back("Some string");

map_str_vector["Some_Key"] = vec_active_channels;

Later in the code, I was erasing an element from the vector like this:

std::vector vec_temp = map_str_vector["Some_Key"];

vec_temp.erase(0);

But you know what, later on when I examined the vector, its size won't be changed.

The reason is when I did:

std::vector vec_temp = map_str_vector["Some_Key"];

A new object of std::vector was created and placed in vec_temp, and the call

vec_temp.erase(0);

was erasing first element from the new object.

The right way to remove a std::vector from a std::map value field is given below

map_str_vector["Some_Key"].erase(0);

We can put an if statement behind this erase operation, to check whether this key exists in the map or not.

C/C++ Common interview questions

2009-02-18T18:10:00.000+05:00

Hi people, I got 2 years of experience and looking for a new job these days. I thought to write down the most commonly asked technical questions, they asked me.

Questions

What is the difference between new/delete and malloc(), free()?
What if we allocate memory using new and release it with free()?
Why do we need virtual destructors?
C++ compiler provides a copy costructor and overloaded assignment operator by default, why do we need to write our own copy constructors?
Have you ever used STL, why do we use STL, if yes then what containers?
What are function pointers?
What happens when a callback funtion is called?
Differences between C and C++?
Write a program in C language which prints "Hello World!" on screen, without using even a single semi colon ';'.
Swap two integers without using a third one.
If we have a struct struct ABC{int n; char c;}; Suppose an integer takes 4 bytes. How many space in memory will be occupied by an instance of this structure?
Why do we need pure virtual functions?
What are friend functions?

Answers

malloc() and free() are C language functions used to allocate and free memory. These funtions simply allocate memory for a variable. new/delete are C++ language operators, new operator allocates memory needed by an object and then calls the constructor function of that object to perform any initializations. Applying delete to an object causes a call to the destructor function of that object, and afterwards a release of memory.
The memory occupied by the object will be returned to Operating System, but the destructor of that object won't be called.
Suppose you use delete with a base class pointer to a derived class object to destroy the derived-class object. If the base-class destructor is not virtual, then delete, like a normal member function, calls the destructor for the base class, not the destructor for the derived class. This will cause only the base part of the object to be destroyed.
C++ default copy constructor and assignment operator perform a member to member copy of the instance variables contained by an object. If we have instance variables of pointer types in an object say object1, and we perform a straight member to member copy to object2. The pointer type instance variables in both object1 and object2 will be pointing to same memory locations. And if we delete one object, the pointers in other object will become invalid without that object ever knowing. This will cause a program crash.
Standard Template Library is a standard peer revised and optimazed collection of containers and algorithms. Because it is standard, it is cross platform and any compiler supporting C++ standards must work with STL. Using STL cuts developement time, and increases program reliablity. I have personally used vector, queue, and map containers.
Callback funtions are also known as delegates. Callbacks are used when we want a method to be called from some other thread of execution. For example the boost::regex_grep function, its parameters are a large(or maybe small) string, a regular expression, and a call back funtion. The string can be very very long and finding the matches may take too much time, so whenever this boost::regex_grep funtion finds a match satisfying the supplied regular expression it will call the funtion in our code specified in callback argument.
A callback funtion is basically a pointer to the starting location of some code, AKA funtion pointer. When a callback funciton is called, its parameters are pushed to stack. Then the control is transferred to the funtion pointer location and then the control resumes from the function pointer location.
C is a functions based language, and it does not provide anything to group data with funtions which will manipulate that data. C++ is an Object Oriented language, and it provides rich constructs to group data with funtions which will manipulate it (AKA Data Encapsulation). It is possible to implement solutions close to real world using C++, by implementing heirarchical designs. C++ saves developement time by code resue through Inheritance as well.
void main(void){if(printf("Hello World!")){}}
int a = 10; int b = 20; a = a+b; b = a - b; a = a - b;
An instance of this struct will take 8 bytes, because the C++ language compiler performs memory padding at every 4 bytes.It means, that a variable occupies at least 4 bytes in memory. 4 bytes is the basic unit of allocation in memory. This struct will take 4 + 1 = 5 bytes in memory, but the compiler will scale it up to 8 bytes by memory padding.
If a class includes a pure virtual function, it can't be instantiated. A class which contains a pure virtual function is an abstract class. Abstract classes are also known as interfaces. In situations where we are defining interfaces, which will be used to contain pointers to child class objects only there must be some way to stop people from creating objects of these interfaces. Pure virtual functions server the purpose. Because an it compiler will stop us from creating an object of an Abstract class.
Friend funtions are funtions which are not the members of a class, but can access the private members of an instance of that class.

Passing NULL as output parameter

2009-01-30T19:29:00.001+05:00

Although it seems okay, but its not okay to pass a variable initialized with NULL as out parameter to a function.

For example, I was doing this once upon a time
SomeClass *objSomeClass = NULL;
SomeFunction(objSomeClass);
// where SomeFunction is supposed to return something in objSomeClass
// This code is correct by syntax, but created problems for me.

The right thing to do is

SomeClass * objSomeClass = new SomeClass();
SomeFunction(objSomeClass);

cheers all...

More on Sockets

2009-01-30T19:22:00.000+05:00

I was writing server side code which will be reading commands from a client over a Win32 socket, problematic code was like this

// suppose m_sock is a working socket, all we gotta do is start receiving data on it

const int nBuffSize = 256;

int nRecv = 0;

char * szCmdBuff = new char [nBuffSize];

memset(szCmdBuff, 0, nBuffSize);

while(1){

nRecv  = recv(m_sock, szCmdBuff, nBuffSize, 0);    

// do something with the data

memset(szCmdBuff, 0, nBuffSize);

}

Problem created by this code: Junk values in input.
Solution: do memset right before calling recv

Exact code to refresh things goes like this

while(1){

memset(szCmdBuff, 0, nBuffSize);

nRecv  = recv(m_sock, szCmdBuff, nBuffSize, 0);    

// do something with the data

memset(szCmdBuff, 0, nBuffSize);

}

cheers all...

Mistakes, not to be forgotten

2009-01-30T19:15:00.001+05:00

Socket Programming:

Was writing a socket server few days back. The code was not working, it goes like(omitting error checks)

SOCKET g_sock_server;
g_sock_server = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
bind(g_sock_server, (LPSOCKADDR) &g_addr_server, sizeof(g_addr_server));
listen(g_sock_server, SOMAXCONN);

SOCKADDR_IN addr_cli;
SOCKET s_cli;
int nSize = 0;
s_cli = accept(g_sock_server, (LPSOCKADDR)&addr_cli, &nSize);
if(s_cli == INVALID_SOCKET) return;
// rest of the code... say blah blah blah blah

The method accept will always return INVALID_SOCKET, guess why?

because of

int nSize = 0;

The fix is

int nSize = sizeof(addr_cli)

cheers all...