Explain me how this constructor works!

[Nio74]

this is the constructor:

ClientServices::ClientServices(const QString hostAddress, int portNumber) : QObject (),m_nNextBlockSize(0)
{

I would like to understand after colon.(m_nNextBlockSize(0) it's declared on the header file like this "quint16 m_nNextBlockSize;" why?

can you give me some tips about the type of constructors? Not having much experience I need help i don't understend them very well..

[ODБOï]

@Nio74 hi, the constructor will initialize that quint16 m_nNextBlockSize declared in the header

[mrjj]

Hi
After the ":", its actually an initialization list
https://en.cppreference.com/w/cpp/language/initializer_list

basically its another syntax for
m_nNextBlockSize =0;

so its a way to set member variables during construction.

[Nio74]

@LeLev said in Explain me how this constructor works!:

@Nio74 hi, the constructor will initialize that quint16 m_nNextBlockSize declared in the header

why do you decare(quint16 m_nNextBlockSize ) in the constructor when it's already declared in the header file?

[mrjj]

@Nio74
hi
it doesn't declare there. ( there is no type, just the name)
it just sets its value.

[Nio74]

@mrjj but then when it is declared in the header file it has no value, and instead by calling it in the constructor it is given a value which in this case is 0 , right?

[hskoglund]

@Nio74 Yes, but since this example is for Qt 4.8 and kind of old, starting with C++11 you can also kill two birds with one stone by just declaring the that value directly in the header file, like:

quint16 m_nNextBlockSize = 0; 

[Nio74]

Tanks to everyone for help me.