about wrapper classes and namespace

[deepak_kr_mehta]

hello sir
sorry for improper english i am again sending my query

1. what is namespace?what particular purpose std namespace is used?
2. what is wrapper class? please explain with example?
from
deepak kr

[redhead]

The std namespace is required, when using cin, cout and endl among others.
When you declare, that you are using a specific namespace, then you maek sure, that your code will use the implementations of those functions as declared in the std namespace.
If you were to combine your code with code from others, then you might end up with an unexpected error, if you're not addressing the namespace required for your part of the code.
An example:

// the code from others
using err::cout;
using std::cin;
using std:: endl;

int error_function(string error)
{
    cout << error.c_str() << endl;
    return 0;
}

// your code
int my_function(string some_string, string *other_string)
{
    if(some_condition)
    {
        cout << some_string.c_str() << endl;
        other_string = "No user input";
    }
    else
        cin.getline(other_string, '\n');
    return 0;
}

If you're not declaring, that you're using std namespace you will be using the err namespace of cout, which could be whatever the previus coder declared that as, beeing writing to stderr, stdout, a file or whatever.
Now if you in your code, specificaly tells it to be using std namespace you're sure that what ever you parse to cout, will allways end up where the std namespace redirects it, usualy stdout.

[Valmont]

You also could take a peek at this thread. Very a amusing thread as well:
return types

[Valmont]

Oh what is left is the "wrapper class". Well a wrapper class is basically nothing else but a class to wrap certain (possibly complex) matters into a single class.

Here a few examples:

1).
A C++ programmer encounters a bunch of C code. It may not be optimized for object oriented programming, or it may not be very user friendly. The C++ coder decides to wrap the C code into a C++ class to implement some form of design or user friendlyness.

2).
In large(r) projects, it may be better to wrap compiler, debug, optimization and test stettings into a single class. The programmer is able to use the settings from a central point.