C++ % " ?

Konstantin Tokarev

@J.Hilk
LOL, I don't know about Boost. But how's about the subject of this post: how is this QString % operator related to original modulus?

modulus has no established meaning for strings, and % looks somewhat similar to + :)

Konstantin Tokarev

Though you should better define QT_USE_QSTRINGBUILDER and simply use + everywhere instead of %

JonB

@Konstantin-Tokarev said in C++ % " ?:

Though you should better define QT_USE_QSTRINGBUILDER and simply use + everywhere instead of %

Ooohhh, the plot thickens...!

J.Hilk

@JonB Qt has ome confusing operaters as well.

for example take QVectors +=

QVector<T> QVector::operator+(const QVector<T> &other) const

I would asume this to be Vector addtion

QVector v1{a,b,c};
QVector v2{d,e,f};

//What one would expect
v1 += v2; -> {a+d, b+e, c+f}

//what one gets
v1 +=v2; _> {a,b,c,d,e,f}

I mean, this technically makes sense. QVector is to generic to have this operation, thats why there is QVector2D, 3D, 4D etc

It still confused me the first time I used it. I did not expect += to be equal to .append() or <<;

In this paticular example I have would prefere a missing += operator :-).

jsulm

@J.Hilk To be honest I would be rather confused if it would do

v1 += v2; -> {a+d, b+e, c+f}

A vector is not a number or something, it is a container. Or is it because it is called "vector" and you expect it to behave like a vector in math? :-)

koahnig

@jsulm said in C++ % " ?:

@J.Hilk To be honest I would be rather confused if it would do
v1 += v2; -> {a+d, b+e, c+f}
A vector is not a number or something, it is a container. Or is it because it is called "vector" and you expect it to behave like a vector in math? :-)

That is debatable and apparently dependent on your background. The foprm you find confusing would be the most logical version for me.

J.Hilk

@jsulm I used to use only QList as a container, and one day I needed to do Vector operations. In my youthfull naiveté I assumed QVector = linear algebra vector.
I learned quickly thats not the case 🤷

Ever since, I prefere using QVector over QList.😉

jsulm

@koahnig Yes, that's true.
@J-Hilk I'm actually wondering why it is called vector? Something like "QDynamicArray" would be less confusing.

koahnig

@jsulm

In the mathematical sense it is alwways a vector, but in spaces with different dimensions. All operators are bascially identical, therefore "real" engineers can accept this. Personally I doubt that the definition of basically changing the space dimension during an addition is conform with pure mathematics. On the other hand you never know what they think/thoght in those areas ;)

kshegunov

@jsulm said in C++ % " ?:

I'm actually wondering why it is called vector?

In linear (and higher) algebra, a vector is an ordered set, or more precisely (and formally speaking) - it is the element of the linear space defined over a field; usually the field of real or complex numbers. Very similar to what you call a vector in programming.

It's just convenience that in Qt you have the + defined to mean merging of two arrays, and not the mathematical operation, as you don't regularly require the mathematical properties of a vector; it's just not so useful in everyday life.

JKSH

@J.Hilk said in C++ % " ?:

@JonB Qt has ome confusing operaters as well.

for example take QVectors +=
QVector<T> QVector::operator+(const QVector<T> &other) const
I would asume this to be Vector addtion
QVector v1{a,b,c};
QVector v2{d,e,f};

//What one would expect
v1 += v2; -> {a+d, b+e, c+f}

//what one gets
v1 +=v2; _> {a,b,c,d,e,f}
I mean, this technically makes sense. QVector is to generic to have this operation, thats why there is QVector2D, 3D, 4D etc

It still confused me the first time I used it. I did not expect += to be equal to .append() or <<;

In this paticular example I have would prefere a missing += operator :-).

Wait till you try + or += on QJsonArray ;)

QJsonArray a1{1, 2, 3};
QJsonArray a2{4, 5, 6};

a1 += a2;
// a1 now has 4 elements: 3 numbers and 1 array

J.Hilk

@JKSH said in C++ % " ?:

Wait till you try + or += on QJsonArray ;)

QJsonArray a1{1, 2, 3};
QJsonArray a2{4, 5, 6};

a1 += a2;
// a1 now has 4 elements: 3 numbers and 1 array

😑😔
of course it does.

Not a fan!