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  

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'.

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.

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

SELECT TABLE_NAME, ENGINE FROM information_schema.TABLES WHERE TABLE_NAME='mytable' AND TABLE_SCHEMA='mydatabase';

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..

Qt C++ to Qml Communication using qmlRegisterUncreatableType()

In this article i will discuss about how to access the C++ class  enum types and attributes in qml file using Qt c++ qmlRegisterUncreatableType() template function.

qmlRegisterUncreatableType() will register the c++ class type (derived from QObject) as the non-instantiable type with QML type system. So we can not create object for the class in qml file, but we can use the properties ans enumerated types belongs to this class in qml file.

To access the enum values in qml , we have to make it available to meta-object system with the following macro, Otherwise we cannot access in qml file.

Q_ENUMS(enumType)

To Register the c++ type with qml type system

 qmlRegisterUncreatableType("ModuleName/uri", MajorVersion, MinorVersion, "QmlName", "message");

Here i'm providing the sample code to demonstrate the use of qmlRegisterUncreatableType() to access c++ class attributes and enum types.

Bit Operations: Qt Example

In this post i'm going to show you some bit operations with &, |, <<, >>, ~ using Qt example. This example include operations like set a particular bit in the given number, clear bit, check bit is set or not and to check whether the number is even or odd.

Following demonstrates the psuedo code of the operations.

> To Set a bit in the given number : perform Betwise OR (|) operation with  1 left shift(<<) by index of the bit to set

     num = num | (1<<index);

>To clear a bit in the given number: perform Betwise AND (&) operation with the inverted(~) 1 left shift(<<) by index of the bit to clear

    num = num & ~(1<<index);

'Cannot find -lGL' error while building the Qt widget application in Linux OS?

Hi all,

Did any one get "Cannot find -lGL" error while building the Qt widget application in Ubuntu operating system? Qt installer provides compiler, debugger, make and other tools for the development. But when you want to develop Qt graphical based application it requires Open GL libraries.

Most of the Linux OS will not provide Open GL libraries as default. To continue building Qt graphical applications just install this libraries.

For Ubuntu use the following command