CMake has a CMAKE_BUILD_TYPE option for predefined build types. The build type affects optimization and whether the result of the build is debuggable. Those used by MySQL are RelWithDebInfo or Debug.
RelWithDebInfo (optimizations are on, debug info is generated) is used in MySQL by default.
Debug (optimizations are off, debug info is generated) is used if the WITH_DEBUG option is set.

CMAKE_BUILD_TYPE is not set when custom compile flags are used

To define which C and C++ compilers to use, you can define the CC and CXX environment variables. For example:

To specify your own C and C++ compiler flags, for flags that do not affect optimization, use the CMAKE_C_FLAGS and CMAKE_CXX_FLAGS CMake options:

When providing your own compiler flags, you might want to specify CMAKE_BUILD_TYPE as well.
For example, to create a 32-bit release build on a 64-bit Linux machine, do this:

If you set flags that affect optimization (-Onumber), you must set the CMAKE_C_FLAGS_build_type and/or CMAKE_CXX_FLAGS_build_type options, where build_type  corresponds to the CMAKE_BUILD_TYPE value.

To specify a different optimization for the default build type (RelWithDebInfo) set the CMAKE_C_FLAGS_RELWITHDEBINFO and CMAKE_CXX_FLAGS_RELWITHDEBINFO options.
For example, to compile on Linux with -O3 and with debug symbols, do this:


List of build-specific variants to specify your Qt project.

QSqlDatabase connection testing tool

QSqlDatabase connection access

A simple 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. An instance of QSqlDatabase represents the connection. The connection provides access to the database via one of the supported database drivers (MySQL in our case), which are derived from QSqlDriver. Alternatively, we can subclass your own database driver from QSqlDriver. I’ll post an another article about how to write your own database driver in Qt for Unix, OSX and Windows platforms. It’s recommend to write your own database driver especially when you planning to deploy your application in different platforms. It’s simply because there could be surprises especially on client deploying your application that using one of the supported database drivers due to missing dependencies or environmental variables.

Software prerequisites:
Remote MySQL server version: 5.7 or above
Qt version: Qt_5_7_1 or above
OpenSSL 1.0.x or above the for SSL feature

How to use it:
1. I simply run the mysql_conn_test_database.sql SQL script file to create a test database on the remote server.
2. Set the hostname or IP, port number, username and password. You migth need to create a new database user for this purpose.
[You will need to create SSL certificates for the database server and client in order to test SSL Feature on the MySQL Server.]
3. If everthing is set just simple build and run the project in your QtCreator.

If everything goes well you will recieve the following feedback from your terminal:

QSqlDatabase connection test tool was created and written by Roland Ihasz and it is licensed under the GNU General Public License (GPL) Version 2 or above.

Check out on GitHub. https://github.com/lnrsoft/QSqlDatabase-connection-test-tool




Alternatively, use the following shorter source code to check the connection without any sql query.
 QSqlDatabase connection test tool without query


After spending a quite a bit of time to find the solution of this often-occurring
QMYSQL driver not loaded problem mainly after installing Qt installation in a new software environment, So I thought I am going to share my best practice to fix this issue.
I wasn’t able to establish database connection even if I received the list of available drivers:

QSqlDatabase: available drivers: QSQLITE QMYSQL QMYSQL3 QODBC QPSQL
QSqlDatabase: QMYSQL driver not loaded

The following simple method helps to fix the problem.
On OSX system just simple install or re-install mysql using the flowing command. I usually prefer Homebrew as it fulfils most my requirements and using MacPort when I really no other options available.

then place the following libmysqlclient.18.dylib.zip (180 downloads) file to the path below:

On different Linux distributions I usually apt install or yum install the MySQL package basically the only thing I need to make sure that place the libmysqlclient.18.dylib.zip (180 downloads) file to the following path:

This method solves the QMYSQL driver not loaded issue and allows me to establish database connection, it might work on Windows system as well, however I had not opportunity to try before.
Please, let me know if this method also working for you by dropping a line.

Download: libmysqlclient.18.dylib.zip (180 downloads)


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:

Multi Level Inheritance – HackerRank Challenge Solved in C++

Multi Level Inheritance – HackerRank Challenge Solved in C++

Variable Sized Arrays – HackerRank Challenge Solved in C++

Variable Sized Arrays – HackerRank Challenge Solved in C++

Set STL – HackerRank Challenge Solved in C++

Set – STL – HackerRank Challenge Solved in C++

HackerRank C++ Virtual Functions Challenge

HackerRank C++ Virtual Function Challenge

HackerRank Challenge – Find out the area of a rectangle using C++ inheritance

Rectangle Area HackerRank Challenge

..and a bit longer version.