Serial communication

[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:

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

[J.Hilk]

@Damian7546 yes, but not the cast or assignment fails, but the access of your QByteArray, it doesn't have 3 Bytes in it and you try to access it outside of the range