Serial communication

Christian Ehrlicher

From my pov the parsing is incorrect as there may be more than one message in the buffer so the second (or even the first part of the second) is thrown away.

Damian7546

@Christian-Ehrlicher so how to fix it?

JonB

@Damian7546
Remove only what is used for a message from the buffer, leaving any further unused bytes there might be for appending to create next "message".

Damian7546

@jsulm
This conversion doesn't work.

class Response
{
public:
    enum class Status : quint8{
         DISABLE = 0x1A,
    };
    Response();
};

In m_responseStatus variable I have 0x1A value, but below statement is not equal:

m_responseStatus = static_cast<Response::Status>(m_request.mid(2,1).toInt(nullptr, 16));
    qDebug() << "m_responseStatus: " << m_request.mid(2,1);

    if(Response::Status::DISABLE == m_responseStatus)
        qDebug() << "ok convert";
    else
        qDebug() << "bad convert";

Problem is in toInt conversion:

qDebug() << "m_responseStatus: " << m_request.mid(2,1);
qDebug() << "m_responseStatus: " << m_request.mid(2,1).toInt(nullptr, 16);

result:
m_responseStatus: "\x1A"
m_responseStatus: 0

JonB

@Damian7546 said in Serial communication:

In m_responseStatus variable I have 0x1A value, but below statement is not equal:

Sorry, I don't believe that. Start with:

qDebug() << int(m_responseStatus)  << int(Response::Status::DISABLE) << 0x1A;

[I assume int() is good enough here to test. You can go static_cast<int>(...) if necessary.]

Damian7546

@JonB said in Serial communication:

Sorry, I don't believe that. Start with:
qDebug() << int(m_responseStatus) << int(Response::Status::DISABLE) << 0x1A;

Result:
0 26 26

JonB

@Damian7546
So you have your answer from the first 2 outputs. 0 != 26, the two values being compared are indeed not equal/the same.

Behaviour is quite correct given your m_request.mid(2,1).toInt(nullptr, 16);, which (QByteArray::toInt()) is quite incorrect to use on your byte array containing a byte with value \x16 (26). toInt() is not for use in your case, as you do not have a string representation of an integer to convert.

Damian7546

@JonB So ho to compare Response::Status::DISABLE to byte in QByteArray m_request[2] ?

JonB

@Damian7546
Exactly as you have just written it!

qDebug() << Response::Status::DISABLE << m_request[2];

[You may have to do casting.] Sightly better is to use m_request.at(2) in place of m_request[2] here, but that is a detail and not related to your issue. You want to inspect the actual bytes in the QByteArray, not call QByteArray::toInt().

J.Hilk

@JonB casting is highly suggested, as Response::Status is an uint_8t and at() returns a char, aka int8_t

JonB

@J-Hilk
Yes, but what I meant is I don't have anything available to test what compiler says as I write answers. So that detail is left to OP :) Since the OP asks about comparing (with ==) one should be able to compare a unit_8t against a char/int8_t, I think, using C++ automatic expression promotion without bothering to cast/convert, I think? But maybe not/warning for enum value against integer?

The important thing is no QByteArray::toInt() here!

Damian7546

@JonB It doesn't work:
qDebug() << static_cast<int>(Response::Status::DISABLE) << m_request.at(2);

Result:
ASSERT: "uint(i) < uint(size())" in file C:/Qt/5.15.2/mingw81_32/include/QtCore/qbytearray.h, line 500

And this way:
qDebug() << static_cast<int>(Response::Status::DISABLE) << m_request[2];

Result:
Bez tytułu.jpg

Where :
m_request response: "\xFC\x05\x1A\xF4\xE8"

JonB

@Damian7546
How difficult to try:

qDebug() << static_cast<int>(Response::Status::DISABLE) << static_cast<int>(m_request[2]);
// or
qDebug() << static_cast<int>(Response::Status::DISABLE) << static_cast<int>(m_request.at(2));

? I leave you to resolve the C++ to your satisfaction.

J.Hilk

@JonB said in Serial communication:

one should be able to compare a unit_8t against a char/int8_t, I think, using C++ automatic expression promotion without bothering to cast/convert, I think?

nono, comparing different types via == or != will never promote any side "automatically"

you can get something like that fi you wrap it in a function call or something but.

But comparing uint8_t and int_8 will only work correctly if both values are between 0 and 128.

Damian7546

@JonB Sill of topic.
I have variable: Response::Status m_responseStatus.
How properly assign byte form QByteArray to m_responseStatus?

J.Hilk

@Damian7546 you were originally pretty spot on:

static_cast<Response::Status>(m_request.at(0));

JonB

@J-Hilk said in Serial communication:

nono, comparing different types via == or != will never promote any side "automatically"

Umm, C or C++

    char c('A');
    if (c == 65)
    {}

example.cpp
Compiler returned: 0

From Godbolt. That's "automatically promoting" char c to int 65, per C/C++ expression rules. Has done since K&R... ?
https://en.cppreference.com/w/cpp/language/implicit_conversion, e.g. Integral conversions topic.

JonB

@J-Hilk said in Serial communication:

static_cast<Response::Status>(m_request.at(0));

I trust healthy disagreement in polite spirit is allowed. Personally, for style, I would not cast an arbitrary integer value to an enumeration, where it might fall outside the range of values. I would prefer

if (static_cast<int>(Response::Status::DISABLE) == static_cast<int>(m_request.at(2))

which is what I wrote earlier, so doing the casting to int.

J.Hilk

@JonB said in Serial communication:

which is what I wrote earlier, so doing the casting to int.

yes I agree, but not what the op asked.

From Godbolt. That's "automatically promoting" char c to int 65, per C/C++ expression rules. Has done since K&R... ?

fair! Not what I had in mind when I wrote my answer and not the pitfall I fell into numerous times :D

Damian7546

@J-Hilk It still doesn't work:
m_responseStatus = static_cast<Response::Status>(m_request.at(2));

Result:
ASSERT: "uint(i) < uint(size())" in file C:/Qt/5.15.2/mingw81_32/include/QtCore/qbytearray.h, line 500