Why no std::byte in qt?!!

Engelard

Situation:
For last 3 hours i tried to figure out whats wrong with my code which i successfully ported in Qt. Now i find reason - qt betrayed me.

I brought my code from VS to Qt. I runned it, everything seems fine,no errors in compile/runtime but program did'nt succeed. Then for next 3 hours i was looking where i made a mistake and found it.

In vs i had

using namespace std;

for nicer code. But in Qt i forgot about that. So, as i understand Qt have it's own, embedded 'byte' type. And when i tried add prefix to my code like 'std::byte' compiler tells me "byte is not part of standard library".

Wut? And then i goes to description of type, found that this type comes from <cstddef> so i included it, but nothing changed, still have only wrong byte from qt which is different.

Tried to replace with QByteArray, but ofcourse it not working. Because i need somehow to use proper one: https://en.cppreference.com/w/cpp/types/byte

kenchan

@Engelard
As far as I recall whether or not you have an std::byte type is dependent on your system and nothing to do with Qt.
It just may or may not be defined in your machines standard library.
BTW std::byte is a C++17 thing.

jsulm

@Engelard said in Why no std::byte in qt?!!:

qt betrayed me

Sorry, but before complaining about Qt you should check what std::byte actually is.
As @kenchan said std::byte is part of C++ standard library (as everything in std namespace).
Furthermore std::byte is part of C++17 standard, that means: you need a C++ compiler supporting C++17.
See https://en.cppreference.com/w/cpp/types/byte
What compiler do you use?
This problem is completely unrelated to Qt.

J.Hilk

@Engelard said in Why no std::byte in qt?!!:

In vs i had
using namespace std;
for nicer code. But in Qt i forgot about that.

And thats one of the reasons I don't use using namespace at least globaly for a class, one should always be certain what one is actually referencing/using

That makes me also a non user of auto, if I can avoid it.

Engelard

@jsulm said in Why no std::byte in qt?!!:

This problem is completely unrelated to Qt.

It works in VS, and not working in Qt. And you telling me that "completely unrelated"? How your argument should work?

JohanSolo

@Engelard said in Why no std::byte in qt?!!:

It works in VS, and not working in Qt. And you telling me that "completely unrelated"? How your argument should work?

Well, Qt is no compiler... it's a framework. Therefore the argument holds.

Engelard

@jsulm said in Why no std::byte in qt?!!:

What compiler do you use?

alt text

Engelard

@JohanSolo said in Why no std::byte in qt?!!:

Well, Qt is no compiler... it's a framework. Therefore the argument holds.

I don't understand. Each IDA must have it's own compiler, no?

Engelard

Just tell me what should i do to be able to use std::byte in qt...

P.S. this topic for some reason became 'auto topic', but this keyword wont work for my case because it can't convert in proper 'raw byte' type because there is no such thing in my Qt(yet).

kenchan

@Engelard
No, the Qt IDE is not a compiler, it provides you with the ability to use whatever compiler you have installed and is compatible with the version of Qt you are using.
In the case of the VS IDE it just happens to be provided by Microsoft and they also provide their own compiler as part of the package. That is just the way it is!

If you want to use the c++17 features in Qt Creator you must tell the compiler you want to use it by putting CONFIG += c++17 in your pro file.
EDIT:
Another way to make it use the c++17 features is to add QMAKE_CXXFLAGS += -std:c++17 this should be equivalent to the above if you use the correct compiler.
I think it will only work the the 15.0 compiler, I tried it with the 14.0 compiler and the complier did not like it. I don't use Qt with the 15.0 version yet so I can't test that.

VRonin

@Engelard said in Why no std::byte in qt?!!:

what should i do to be able to use std::byte in qt

Just chose as a compiler VS 2017.3 [P2] or later (i.e. the compiler 15.0)

Each IDA must have it's own compiler, no?

Absolutely not.

this topic for some reason became 'auto topic',

Forked to https://forum.qt.io/topic/95412/rants-about-auto

Engelard

@kenchan said in Why no std::byte in qt?!!:

I think it will only work the the 15.0 compiler, I tried it with the 14.0 compiler and the complier did not like it. I don't use Qt with the 15.0 version yet so I can't test that.

Did'nt work out((

@VRonin said in Why no std::byte in qt?!!:

Just chose as a compiler VS 2017.3 [P2] or later (i.e. the compiler 15.0)

Which one should i choose?:

alt text

And then. Where and for what exactly file should i looking at? Can i add same compiler from my VS2017?

VRonin

@Engelard said in Why no std::byte in qt?!!:

Did'nt work out((

What did you do?

Engelard

@VRonin like @kenchan said, add in to .pro file one of these:

CONFIG += c++17
QMAKE_CXXFLAGS += -std:c++17

Non of them worked. Still no byte type in std::

VRonin

Can you show us what kit are you building with? see image below:

Engelard

@VRonin I just added first manual compiler, which from folder of my VS2017 Community, still it says that byte is not part of std.

alt text

Here it is:

alt text

Did i did that correct?

Engelard

Oh and in the Kits i just now noticed, for some reason there is compilers for amd chosen, when i have normal for intel i suppose in my VS. And i can't change it, when i press manage - it's simply throw me in to compilers tab so i don't know how to change it:

alt text

AND. i just now added one more custom compiler, also from VS2017 but 64 version, since i have x64 CPU and windows, maybe should be proper one, am i right?

alt text

Only one thing (as i understand) left to do. Is apply compiler which i chose in 'compilers' tab, because there is still my old as you can see from screenshot

alt text

jsulm

@Engelard "How your argument should work?" - easy. You should understand the difference between a compiler, an IDE and a framework. Qt is a C++ framework (not a compiler), QtCreator is an IDE which supports many different compilers, but does not contain own compilers. C++standard library (std::*) comes as part of the compiler and NOT Qt, that's why it is "completely unrelated to Qt". So, as already explained by others you need a compiler supporting C++2017 and activate C++2017 supports in the pro file (not sure it is needed with Microsoft compilers).

Didn't QtCreator auto-detect your VS2017 compiler? Usually there is no need to configure compilers manually. The 15.0 is already the C++ compiler from VS2017, why do you add the compiler manually? Does it now work with your "Desktop Qt 5.10.1 MSVC2017 64bit2" Kit and autodetected VS2017 compiler?

One note: an IDE does not have to contain any compilers. Microsoft Compilers can be installed and used without Visual Studio. The reasons are: it must be possible to use compilers without a huge IDE (for example in a continuous integration system) and many IDEs (like QtCreator) support different compilers which come from different companies or are open source. QtCreator, for example, supports Microsoft Compilers and MinGW on Windows. Qt Online Installer for Windows provides the possibility to install MinGW as it is Open Source. Microsoft compilers on the other hand can't be provided by Qt Online Installer as this not allowed by Microsoft.

VRonin

@Engelard said in Why no std::byte in qt?!!:

still it says that byte is not part of std.

Did you #include <cstddef>?
Can you open Visual Studio 2017, create a simple console program and test if it works there?

kshegunov

@Engelard said in Why no std::byte in qt?!!:

there is compilers for amd chosen, when i have normal for intel i suppose in my VS

This is the CPU instruction set. Intel processors use amd64, so it's correct.