Thursday, March 9, 2017

Multi-character literal (Multiple characters inside single quotes) Vs char literal in C, C++

Any character with in single quotes('a') is a character literal  (character constant) and a string literal is a set of characters with in double quotes ("Hello").
And if we have multiple characters in side single quote('aa') ,it is a multi-character literal

Before going to the multi-character literal we will check how these literals are considered (as value and type) by compiler. In C language type of character literal is int. So size of char literal is 4 bytes in 32 bit architecture. Where as in C++ the type of character literal is char and size is 1 byte.

Save following program with .c and .cpp extension and run with c and cpp compiler.

Wednesday, March 8, 2017

When to use dynamic_cast and static_cast in C++

Dynamic Cast:
  • Dynamic cast is used to convert a pointer (or reference) to base type to pointer (or reference) to derived type, iff the base pointer/reference refers to derived type. This is called down casting. (Base -> Derived)
  • This type of casting is used when these two types are polymorphic (means base class should have virtual methods).
  • No need of explicit type casting when we want to convert a pointer (or reference) to derived type to pointer (or reference) to base type. This is called up casting. (Derived-> Base )
  • If you use dynamic_cast for non-polymorphic classed it will through compile time error
  • This cast is mainly used to execute the derived type specific functionality when we have base class pointer/reference. (Throgh base pointer/reference we cannot access derived type specific fucntionality)
  • dynamic_cast safely convers to derived type in run-time, if it fails to convert it will return NULL when target is pointer type, throws bad_cast exception when target type to convert is reference.

Sunday, January 8, 2017

C++11 Features (Part 1)

Here i'm listing some of the C++ 11 features we can use frequently.

2.Range Based for loop
3.Strongly typed enums
4.Forward enum declaration

To use C++ 11 features when compiling in commad line use any of the following flags

  $g++ -o myprog myprog.cpp -std=c++0x  (or)  
  $g++ -o myprog myprog.cpp -std=gnu++0x (or)  
  $g++ -o myprog myprog.cpp -std=c++11    

Before C++11 auto keyword is used in the storage class, from C++11 it is used as type inference, means automatic deduction of data type of an expression.
We can use auto inside the blocks, namespaces, and for loop initialization etc. Using auto we can reduce writing the some complex type declarations like iterators intialization in loop.

Monday, December 19, 2016

How to use Valgrind for debugging C/C++ program

Valgrind tool is used to for memory leaks, uninitialized memory, reading or writing to memory that has been freed, invalid access to memory(boundary conditions for the dynamic arrays), mismatched use of malloc/new/new[] with free/delete/delete[] , double free/delete.

How to use Valgrind:
>Compile the program with -g option (this option will add debugging symbols), so that we can see line numbers of the program when debugging

 $ g++ -o test -g test.cpp  

Tuesday, September 6, 2016

Dynamic memory allocator: new in C++

In c++ we will use new operator to allocate memory dynamically . In this post we will know how this process happens and what are the steps involved while using new. Basic syntax for new is
new [placemenet-params] typename;
This expression will allocate the memory available from the free store and returns the pointer to the object of type 'typename'. And in case of class, struct types it will allocate memory and intialise the object then retun the pointer to the object 'typename'.

Saturday, July 2, 2016

Object Slicing in C++ with example

What is Object Slicing? 
When an instance of derived class  is copied to base class object by value , part of members associated with derived object will be lost(sliced) . Here base class object discards the data related to the derived class because base class object don't have information about the derived members

When we copy derived obj by value to base obj,  the base class copy constructor /assignment operator will call (copy constructor will call at assigning object at the time of declaration (or) pass by value argument to function and assignment operator will call when assigning object after declarion), so base class don't have information about the derived members to copy.  This means the base copy/assignment will copy members related to base class only.

The following sample c++ code will explain the above description.

Wednesday, June 8, 2016

Some Useful My Sql Queries for beginners

My Sql is a popularly used Relational Database Management System.  Database is used store and retrieve data efficiently with the proven algorithms. Here i'm providing some sql commands which are useful for beginners in my sql queries.

Here information_schema is the default database comes with Mysql installation.

>To check the engine used for the table - mytable

Thursday, May 26, 2016

Maria DB Storage Engines and Alogorithms used for Indexing

Maria DB is a Open source database and is a replacement for My SQL data base after My Sql (Sun Micro Systems) has been acquired by Oracle.

Database can have multiple tables and each table will use one storage engine, and we can use different storage engines for different tables in the database.

In this article i'm discussing about the storage engines of Maria DB. There are many storage engines that supports Maria DB, and these are pluggable engines.

To see the available storage engines in maria db, execute the following query

MariaDB [(none)]> show storage engines;  (or)
MariaDB [(none)]> show engines;
And for all these storage differ from one another with the following properties..