how to pass functions as parameters to another function

rezaMSLM

I want to pass function to another and this is my code:
.h file:

    void Read_Func(QModbusDataUnit::RegisterType reg_type, int Start_Address,
                   int Number_of_Entries, int SlaveID, void (*f)());

.cpp file:

void settings::Read_Func(QModbusDataUnit::RegisterType reg_type, int Start_Address,
                         int Number_of_Entries, int SlaveID, void (*f)())
{

}

ERROR:

 error: [release/moc_settings.cpp] Error 1

mrjj

Hi
The function pointer syntax seems fine.
The error is something else in the .h file ( i would guess)
That error means that the moc tool didnt make moc_settings.cpp

rezaMSLM

@mrjj
if I comment

, void (*f)()

no error is received

mrjj

@rezaMSLM

Is Read_Func listed as a slot ?

I just tried same syntax here and it compiled. so its not syntax it self, i think.

rezaMSLM

@mrjj
yes
in private slots

mrjj

@rezaMSLM
Just tested. got same error.
So moc does not support functions pointers for slot parameters it seems.
http://doc.qt.io/qt-5/moc.html#function-pointers-cannot-be-signal-or-slot-parameters
but you can use the typedef workaround.

aha_1980

@mrjj typedefs makes working with function pointers easier, anyway. Thats why I prefer them too.

mrjj

@aha_1980
Indeed, a typedef makes the code easier to read but also
allow to change the function signature in one place.
So the its a win-win in this case :)

rezaMSLM

I used typedef as mentioned in that link
here is the result:
.h file:

typedef void (*f)();
class settings : public QDialog
{
.
.
private slots:
 void Read_Func(QModbusDataUnit::RegisterType reg_type, int Start_Address,
                   int Number_of_Entries, int SlaveID, f);
.
.
void test();
}

.cpp:

void settings::on_pushButton_Minute_Read_clicked()
{
    Read_Func(QModbusDataUnit::HoldingRegisters, 3, 1,CorrectID,test);//<--error
}

void settings::Read_Func(QModbusDataUnit::RegisterType reg_type, int Start_Address,  int Number_of_Entries, int SlaveID, f)
{
    auto ReadUnit = QModbusDataUnit(reg_type, Start_Address, Number_of_Entries);
    if(auto *reply = ModbusObject->sendReadRequest(ReadUnit, SlaveID))
    {
        if(!reply->isFinished())
            connect(reply,&QModbusReply::finished,[this](){f();});
        else{
            //statusBar()->showMessage("error!;Reply Deleted",2000);
            delete reply;
        }
    }
    else
     ; //  statusBar()->showMessage("error!",2000);
}

void settings::test()
{
    qDebug()<<"test executed";
}

ERROR:

 no matching function for call to 'settings::Read_Func(QModbusDataUnit::RegisterType, int, int, int&, <unresolved overloaded function type>)'
     Read_Func(QModbusDataUnit::HoldingRegisters, 3, 1,CorrectID,test);
                                                                     ^

mrjj

Hi
you have test() as part of a class and hence its not a c function pointer as your
declaration suggest. ( the typedef)
So either move it outside class or make it static.
or use a member function pointer so that the info needed to call it is included.
https://isocpp.org/wiki/faq/pointers-to-members

rezaMSLM

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