How to use QVector with double

[CJha]

Hi! It might seem like a silly question but I am unable to initialize QVector. Here is what is happening:

QVector<double> vec(10); // Error: Expected a type specifier

I am initializing this in my .h file and I am using #include <QVector>. Isn't this how we are supposed to initialize QVector?

[Chris Kawa]

Isn't this how we are supposed to initialize QVector?

Yes and no. This is how you'd initialize a local variable in a function.
If it's a class member you can initialize it like this

QVector<double> vec = QVector<double>(10);

or with braces if it's not too much to type:

QVector<double> vec {0,0,0,0,0,0,0,0,0,0};

[CJha]

@Chris-Kawa Thank you! I knew it had to be something simple like this but was unable to find it on the internet.

[Chris Kawa]

To be honest initialization in C++ is a bit of a mess and it's easy to get it wrong.
There's a nice talk about this and related stuff from few years back: "The Nightmare of Initialization in C++".

[J.Hilk]

@Chris-Kawa said in How to use QVector with double:

or with braces if it's not too much to type:

QVector<double> vec {0,0,0,0,0,0,0,0,0,0};

or

QVector<double> vd(10,0.0);

if its too much to type , but the same value

[CJha]

@Chris-Kawa Yeah, sometimes it is very frustrating with simple things, especially since I am new to C++. Tanks for the video link, I will watch it soon in my spare time :)

[Chris Kawa]

@J-Hilk said:

QVector<double> vd(10,0.0);
if its too much to type , but the same value

That's not gonna compile as a class member declaration. As a local variable it's the same as QVector<double> vd(10) as 0.0 is the default value for double.

[J.Hilk]

@Chris-Kawa

fair enough 😉

but,
...
as member initialization, you could do:

QVector<double> vec2{QVector<double>(10)};
QVector<double> vec{QVector<double>(10,0.0)};

you're right, there are way to many ways to initialize stuff in c++ !