So its all about last 3 months…. Finally I left the Convergys . Personally I enjoyed a lot at Cvgs. I love Cvgs, I spend all my 6years of infant stage. In 2004[don't ask me whether I love Convergys or its people, no doubt, its Cvgs, as opposite to R.Narayanmurthy views], when I was looking for a job after graduation, Convergys given me a chance to appear for Written Test[Who will give the chance at that time where a lot people in queue?]. Luckily I got the job after single round of technical interview. Specifically I enjoyed FOOD a lot and Transport facility. No Convergian will forget this,bet. I joined in SPIRNT team at beginning and with VIVO team when leaving. I never forget some of my management ppl like Samit, Raman and Shyam. These are people who encouraged me a lot. Anyway, I left Convergys with loads unhappy. The ‘belongingness’ feeling is still with me. I learned both professional and politically [? Hope you understood ]I was proud to be part of it. I hope, my contributions are never wasted. I hope and wish, Convergys will do a good business.

All the best Convergys.

The main difference otherwise is a difference in the speed at which you can access individual elements. Maps are usually stored as binary trees and hash maps are stored as hash tables. This means that if you have N elements in your container, then accessing an element in a map requires O(log(N)) time and the same operation in a hash map is O(1). So hash maps are faster, in general than maps. [Answer is by Yves M]

1) 30-Mar-2010:
- Map and Multimaps: Had a quick look on the STL reference book and still need to do practice
- Why we should not throw exception in dtor
- Tier1,Tier2 applications

Subject: 1. What is a Two-Tier Architecture?
A two-tier architecture is where a client talks directly to a server, with no intervening server. It is typically used in small environments (less than 50 users). A common error in client/server development is to prototype an application in a small, two-tier environment, and then scale up by simply adding more users to the server. This approach will usually result in an ineffective system, as the server becomes overwhelmed. To properly scale to hundreds or thousands of users, it is usually necessary to move to a three-tier architecture.

Subject: 2. What is a Three-Tier Architecture?
A three-tier architecture introduces a server (or an “agent”) between the client and the server. The role of the agent is manyfold. It can provide translation services (as in adapting a legacy application on a mainframe to a client/server environment), metering services (as in acting as a transaction monitor to limit the number of simultaneous requests to a given server), or intellegent agent services (as in mapping a request to a number of different servers, collating the results, and returning a single response to the client.

Subject: 3. What is Middleware?
Connectivity allows applications to transparently communicate with other programs or processes, regardless of their location. The key element of connectivity is the network operating system (NOS). NOS provides services such as routing, distribution, messaging, file and print, and network management services. NOS rely on communication protocols to provide specific services. The protocols are divided into three groups: media, transport and client-server protocols. Media protocols determine the type of physical connections used on a network (some examples of media protocols are Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), coaxial and twisted-pair). A transport protocol provides the mechanism to move packets of data from client to server (some examples of transport protocols are Novell’s IPX/SPX, Apple’s AppleTalk, Transmission Control Protocol/ Internet Protocol (TCP/IP), Open Systems Interconnection (OSI) and Government Open Systems Interconnection Profile(GOSIP)). Once the physical connection has been established and transport protocols chosen, a client-server protocol is required before the user can access the network services. A client-server protocol dictates the manner in which clients request information and services from a server and also how the server replies to that request (some examples of client- server protocols are NetBIOS, RPC, Advanced Program-to-Program Communication (APPC), Named Pipes, Sockets, Transport Level Interface (TLI) and Sequenced Packet Exchange (SPX)).

This is the number of actual objects held in the vector, which is not necessarily equal to its storage capacity. Vectors automatically reallocate their storage space when needed or when requested with member resize. To retrieve the current storage capacity of a vector you can call to its member capacity.
capacity:
Returns the size of the allocated storage space for the elements of the vector container.

Notice that, in vectors, the capacity is not necessarily equal to the number of elements that conform the underlying vector content (this can be obtained with member vector::size), but the capacity of the actual allocated space, which is either equal or greater than the content size.

Notice also that this capacity does not suppose a limit to the size of the vector. If more space is required to accomodate new elements in the vector, the capacity is automatically expanded, or can even be explicitly modified by calling member vector::reserve.

The real limit on the size a vector object can reach is returned by member vector::max_size.
max_size:
Returns the maximum number of elements that the vector container can hold.

This is not the amount of storage space currently allocated to the vector (this can be obtained with member vector::capacity), but the maximum potential size the vector could reach due to system or library implementation limitations.
Example:

[mingle]/home/rjanagam/CPP% cat stl_vector_sizes.cpp
#include
#include

vector v;
v.reserve(5);
cout<< " size=" << v.size()<< ":capacity="<<v.capacity()<<":max_size="<<v.max_size()<<endl;
vector t;
cout<< " size=" << v.size()<< ":capacity="<<t.capacity()<<":max_size="<<t.max_size()<<endl;
vector r(5);
cout<< " size=" << r.size()<< ":capacity="<<r.capacity()<<":max_size="<<r.max_size()<<endl;
vector s(5);
s[0]=1,s[1]=2;
cout<< " size=" << s.size()<< ":capacity="<<s.capacity()<<":max_size="<<s.max_size()<<endl;
vector w;
w.push_back(1);
cout<< " size=" << w.size()<< ":capacity="<<w.capacity()<<":max_size="<<w.max_size()<<endl;
vector b;
for (int i=0;i<31;i++)
b.push_back(1);
cout<< " size=" << b.size()<< ":capacity="<<b.capacity()<<":max_size="<<b.max_size()<<endl;
vector x;
cout<< " size=" << x.size()<< ":capacity="<<x.capacity()<<":max_size="<<x.max_size()<<endl;
}

[mingle]/home/rjanagam/CPP% a.out
size=0:capacity=5:max_size=1073741823
size=0:capacity=0:max_size=1073741823
size=5:capacity=5:max_size=1073741823
size=5:capacity=5:max_size=1073741823
size=1:capacity=32:max_size=1073741823
size=31:capacity=32:max_size=1073741823
size=0:capacity=0:max_size=1073741823

1) Very first, A goto or switch statement shall not be used to transfer control into a try block or into a handler.

Example:
void f () {
     goto l1 ; / / Ill-formed
     goto l2 ; / / Ill-formed
     try {
       goto l1 ; / / OK
       goto l2 ; / / Ill-formed
       l1 : ;
     } catch (...) {
     l2 : ;
     goto l1 ; / / Ill-formed
     goto l2 ; / / OK
}

but, a goto, break, return, or continue statement can be used to transfer control out of a try block or
handler. When this happens, each variable declared in the try block will be destroyed in the context that directly contains its declaration.

lab : try {
        T1 t1;
        try {
           T2 t2;
           if (condition )
              goto lab;
        } catch (...) { /* handler 2 */ }
      } catch (...) { /* handler 1 */ }

2) One more intersting point I got. I executed the below program SunOS 5.10.

[mingle]/home/rjanagam/CPP% cat exception1.cpp
#include

using namespace std;

class T{
 string  _name;
public:
     T(){cout << " T default Constructor..." << endl;_name = "default";}
     T(const char* name):_name(name){cout << name << " - Constructor..." << endl;}
     ~T(){cout << _name << " - Destructor..." << endl;}
};
int main()
{
   T t1("first ");
   try
   {
       T t2("second");
       throw t2;
       try
       {
          T t3("third ");
          throw;
       }
       catch(...){ cout << "Catch 1 Handler..." << endl;}
   }
   catch(...){ cout << "Catch 2 Handler..." << endl;}

 cout << " Exiting Main Program " << endl;
 return 0;
}

And here is the output:

[mingle]/home/rjanagam/CPP% a.out
first  - Constructor...
second - Constructor...
second - Destructor...
Catch 2 Handler...
second - Destructor...
 Exiting Main Program
first  - Destructor...

If you observe the output closely, you will see that “second” destructor is called twice, but constructor is called only once. any guess, why?

Only I know one thing is , “When the control is transffered out of a try block or handler, each variable declared in the try block will be destroyed in the context that directly contains its declaration.”

Ok, I improved the code by adding the copy constructor as below:

class T{
 string  _name;
public:
     T(){cout << " Class T default Constructor..." << endl;_name = "default";}
     T(const char* name):_name(name){cout << name << " - Constructor..." << endl;}
     ~T(){cout << _name << " - Destructor..." << endl;}
     T(const T &in){
         cout << " Copied " << _name.c_str() << " to " << in._name + " Copy" << "- Copy Ctor... "<_name = in._name + " Copy";
     }
};

So here the output:
[mingle]/home/rjanagam/CPP% a.out
first  - Constructor...
second - Constructor...
 Copied  to second Copy- Copy Ctor...
second - Destructor...
Catch 2 Handler...
second Copy - Destructor...
 Exiting Main Program
first  - Destructor...

Again, I want make the copy constructor is as private sothat compiler cannot use that copy constructor for temporaries. So I just tried to make it as private then I got below compilation error.

[mingle]/home/rjanagam/CPP%  CC exception.cpp
"exception.cpp", line 23: Error: T::T(const T&) is not accessible from main().
1 Error(s) detected.
[mingle]/home/rjanagam/CPP%

3) A function-try-block associates a handler-seq with the ctor-initializer, if present, and the function-body. An exception thrown during the execution of the initializer expressions in the ctor-initializer or during the execution of the functionbody transfers control to a handler in a function-try-block in the same way as an exception thrown during the execution of a try-block transfers control to other handlers.

C::C(int ii , double id)
try
: i(f(ii )) , d(id)
{
    // constructor function body
}
catch (...)
{
  // handles exceptions thrown from the ctor-initializer
  // and from the constructor function body
}

4) When an exception is thrown, control is transferred to the nearest handler with a matching type. A throw-expression initializes a temporary object, called the exception object. The type of the throw-expression
shall not be an incomplete type, or a pointer to an incomplete type other than void. The temporary persists as long as there is a handler being executed for that exception. In particular, if a handler exits by executing a throw; statement, that passes control to another handler for the same exception, so the temporary
remains. When the last remaining active handler for the exception exits by any means other than throw; the temporary object is destroyed and the implementation may deallocate the memory for the temporary object; any such deallocation is done in an unspecified way. The destruction occurs immediately after the destruction of the object declared in the exception-declaration in the handler.

5) As control passes from a throw-expression to a handler, destructors are invoked for all automatic objects constructed since the try block was entered. The automatic objects are destroyed in the reverse order of the completion of their construction. The process of calling destructors for automatic objects constructed on the path from a try block to a throw-expression is called “stack unwinding.” If a destructor called during stack unwinding exits with an exception, std::terminate is called. So destructors should generally catch exceptions and not let them propagate out of the destructor.

6)