How to display received float values via rs232.

[A Former User]

There are multiple ways to do it, e.g:

const float f = 23.f;
const QString s1 = QString::number(f); 
const QString s2 = QString("%1").arg(f);

[AnilReddy]

@Wieland
thank you very much for the reply . My project is to display the float values which we will get from FPGA.
we will receive 6 float values, each consisting of 4 bytes. These bytes are equal to the representation of the float values in the memory. In detail: If you define a float variable in your program, then this variable will occupy 32 bit (4 byte) in the main memory. You will have to create a variable for each engine (or an array) and write the received bytes into the memory of these variables. How the memory representation of the float values looks like, For example a float value of 1 is represented with the 32 bit word 0x3f800000.

This the c++ code i have implemented , but i am getting errors . please kindly help me to change this logic .

void SerialConnect::read() {

const float a = 0x3f800000;
const float b = 0x40000000;
const float c = 0x40400000;
const float d = 0x40800000;
const float e = 0x40A00000;
const float f = 0x40C00000;

newSerialDataString = serial->readAll();
QString data=newSerialDataString.trimmed();

if (data == a) {
    serialDataString.append("0x3f800000");
}
else if (data == b)
{
    serialDataString.append("0x40000000");
}
else if (data == c)
{
    serialDataString.append("0x40400000");
}
else if (data == d)
{
    serialDataString.append("0x40800000");
}
else if (data == e)
{
    serialDataString.append("0x40A00000");
}
else if (data == f)
{
    serialDataString.append("0x40C00000");
}
serialDataChanged();

}

[mrjj]

@AnilReddy said:

but i am getting errors

Hi
You should list those errors :)

maybe insert qDebug() << "reading:" << data;

so you can see what data comes in.

[AnilReddy]

@mrjj

this what occurring for all if statements.
no match for operation == (operand types are QString and const float)

[VRonin]

you are doing a lot of invalid stuff

what do you receive in serial->readAll()?
is it 24 bytes (6 floats) or 4 bytes (1 float at a time)?
does it have headers in front of it?
could you show an example of message?

[AnilReddy]

@VRonin

4 bytes for 1 float value at a time.
Actually i am modifying the program which can receive the one byte at a time. I am unable to understand how to change to my requirement now

[AnilReddy]

@VRonin
and these are the float points i will get . each one comes separately . it means one value at a time.
but i do not know how define in header file. could you please tell me how to mention.
0x40000000
0x40400000
0x40800000
0x40A00000
0x40C00000

public:
explicit SerialConnect(QObject *parent = 0);

Q_PROPERTY(QString newSerialData MEMBER newSerialDataString NOTIFY serialDataChanged);
Q_PROPERTY(QString serialData MEMBER serialDataString NOTIFY serialDataChanged);
Q_PROPERTY(QStringList availablePorts MEMBER availablePortsList NOTIFY availablePortsChanged)

private:
QSerialPort *serial;
QString serialDataString;
QString newSerialDataString;
QString a;
QStringList availablePortsList;
QBasicTimer timer;
void connectSerialPort();

[kuzulis]

1. Do not use the "string" representation of a float in your code (as for your signal) as it is overhead, just use:

class Foo : public QObject
{
...
signals:
    void valueChanged(float value);
}

2. Your received code can be looks like:

void Foo::onReadyRead()
{
    while (serial->bytesAvailable() >= sizeof(float)) {
        QDataStream in(serial);
        // setup another QDataStream' properties, as endianless, float precision and etc.
        float value = 0.0;
        in >> value;
        emit valueChanged(value);
    }
}

Of course, you should know the start/stop bytes of your data sequence (your float value)... usually for this purposes are used protocols, where, e.g. with the:

<start_byte><data_length><data><crc><stop_byte>

frames format, or something else...

Otherwise, if you start to read data from the FPGA (if your FPGA sends data continuously) in a spontaneous timepoint, then you can miss from the beginning for float... and to read 4 bytes of garbage and so on.

PS: A simple way, it is when your FPGA sends the float values in the "text" form with the end of each string, e.g.: "123.456\n".. in this case it is simple to parse it.. But this "text" form spent bigger traffic and additional code in FPGA :)

[AnilReddy]

This post is deleted!

[kuzulis]

I have already told everything that I wanted to tell. I don't understand, what you don't understand.

may i know is this the right way please kindly check it.

No no no, please check it yourself. I do not want to check your "monkey's-code".

[AnilReddy]

@kuzulis
I really appreciate for help . you have mentioned a lot for me to understand . As a fresher i am not good at programming . But this not polite to say like that.