C++

SQLite – How to use fundamental functions in C++

SQLite operations in C++

This tutorial aimed to demonstrate how to use SQLite database operations such as CREATE, INSERT, UPDATE, SELECT and DELETE in C++. Since the appearance first smartphone and other mobile devices SQLite become most widely deployed and used database engine in the world. Precise numbers are difficult to obtain but SQLite is likely used more than all other database engines combined. We can find SQLite in every Android device, iPhone and iOS device, Mac, Windows10, Firefox, Chrome, Safari, Skype, Dropbox, TurboTax, QuickBooks, PHP, Python, television sets, set-top cable boxes and many automotive multimedia systems.

It’s an open-source SQL database engine. You can download the source code or precompiled binaries depending your requirements. You might also need to add [-lsqlite3] and [-std=c++17] to successfully compile, create an executable file. Each of the following source code available on my git repository. https://github.com/lnrsoft

Step 1 – The first thing we need to do is to create the actual database file that we will use in this article. I called sqltdemo.db in our case.

Compile and run our source code to create the local_db.sqlite with the following command. Here we link our code with the sqlite3 library that will create our db file.

Verify our result:

Step 2 – CREATE TABLE

Compile and run.

Step 3 – INSERT INTO our CANDIDATE TABLE

Compile and run.

Step 4 – Fetch and display records from the company CANDIDATE TABLE. In this scenario we use a callback function that obtains results from SELECT statement.

Compile and run.

Step 5 – Using UPDATE statement to update any records in our CANDIDATE table.

Compile and run.

Step 6 – DELETE statement can delete any records from the CANDIDATE table.

Compile and run.

I recommend you to check the official SQLite documentation at sqlite.org for more advance SQLite features and options and support. For further info about using sql with c++ you might found it useful to read me previous post of  a simple Qt tool to test QSqlDatabase access connection to a MySQL database. I created this simple Qt command line tool to test connection between Qt client applications and a remote Mysql Server. The code includes Secure Sockets Layer (SSL) support to test secure connection. The QSqlDatabase class provides an interface for accessing a database through a connection where an instance of QSqlDatabase represents the connection. The connection provides access to the database via one of the supported database drivers, which are derived from QSqlDriver.

Alternatively, we can subclass your own database driver from QSqlDriver. My next post will be an article how to write your own database driver in Qt for Unix, OSX and Windows platforms.

[C++] An Interesting Bit Array Example

Here is an interesting bit array task and its solution in C++ that I thought it’s worth to share with you.
You are given four integers values: N, A, B, and C. You need to use them in order to create the sequence called bitArray with the following pseudo-code:

Task: calculate the number of distinct integer in the bitArray sequence.

Solution
Input: four space separated integers on a single line, N, A, B, and C  respectively.
Where N = 32, A = 16, B = 16, C = 16.
Output: 
one integer that denotes the number of distinct integer in the bitArray sequence equals 7 as we set N, A, B, C values.

If you’d like to read the input from the console simply comment out line 57 and 62 and toggle comment selection on line 58, 59, 60 and 61.
Input read from the console:

four space separated integers on a single line, N, A, B, and C  respectively.
Output print to the console: 
One integer that denotes the number of distinct integer in the sequence called bitArray.

The number of distinct integer  in the sequence  will be 536870912 when we change the previously set integer values to:

Use Wandbox online C++ compiler

HOW TO RETURN A STRING EQUIVALENT OF THE NUMBER N USING QT.

QString QString::number(double n, char format = ‘g’, int precision = 6) returns a string equivalent of the number n, formatted according to the specified format and precision.

Let’s see the following example.
There are 3 double values x, y, z.
We want to return the result of the following equation:
(x / z) * (5.961 / y)
We also want to ask the user to set the desired precision of the result.

Here is how I do with Qt.
You can also Fork the complete qt project from my GitHub.
* note = there are many ways to solve this issue, much simpler, but this time I want to demonstrate how we do in Qt.

Argument Formats
In member functions where an argument format can be specified (e.g., arg(), number()), the argument format can be one of the following:

Format            Meaning

e                      format as [-]9.9e[+|-]999

E                      format as [-]9.9E[+|-]999

f                       format as [-]9.9

g                      use e or f format, whichever is the most concise

G                     use E or f format, whichever is the most concise

A precision is also specified with the argument format. For the ‘e’, ‘E’, and ‘f’ formats, the precision represents the number of digits after the decimal point. For the ‘g’ and ‘G’ formats, the precision represents the maximum number of significant digits (trailing zeroes are omitted).

How to return a string equivalent of the number n using Qt was written by Roland Ihasz>, you can modify or distribute. You can do anything you want with this software, just don’t say you wrote it.

More info on   doc.qt.io

Accessing Inherited Functions – HackerRank Challenge Solved in C++

Accessing Inherited Functions – HackerRank Challenge Solved in C++

You and run the code from your terminal using the following commands: