How to define static members in a static function in .cpp file?

thippu

Hi,

I have declared static double sampling_rate; in ampconfigure.h
2)I have static member function asReadIni() in ampconfigure.cpp
3)I did initialize sampling_rate in ReadIni() but getting error like undefined reference to AmpConfiguration::sampling_rate.
How to initialize it properly?.

jsulm

@thippu Please show your code (how you declare the static variable and how you're initialising it).
It sounds like you did not define the static member. You need this in your cpp:

double AmpConfiguration::sampling_rate;

thippu

@jsulm okay.

ampconfiguration.h

static double sampling_rate;
int getSampling_rate()const;
void setSampling_rate(int value);

static void ReadIni();

ampconfiguration.cpp

void AmpConfiguration::ReadIni()
{
   QFile fp("AmpConfiguration.txt");
   if(!fp.open(QIODevice::ReadOnly)
  {
     QMessageBox::information::(nullptr,"file error","file not found",QMessageBox::Ok);
  }
QStringList *line_list=new QStringList;
QTextStream txt_stream(&fp);
while(!txt_stream.atEnd())
{
  QString line=txt_stream.readLine();
  QStringList temp=line.split("=",QString::SkipEmptyParts);
  line_list->push_back(temp.at(1));
 }
   sampling_rate=line_list->at(0).toDouble();
}
//I am getting error in the building itself not on the runtime.

jsulm

@thippu Not really what I asked...
Did you add

double AmpConfiguration::sampling_rate;

to your cpp file?

thippu

@jsulm said in How to define static members in a static function in .cpp file?:

double AmpConfiguration::sampling_rate;

double AmpConfiguration::sampling_rate=10.2 //like this? in the static function?

jsulm

@thippu said in How to define static members in a static function in .cpp file?:

in the static function?

No. Like this:

double AmpConfiguration::sampling_rate=10.2;
void AmpConfiguration::ReadIni()

See https://en.cppreference.com/w/cpp/language/static

thippu

@jsulm yes bro, I did add like this double AmpConfiguration::sampling_rate=line_list->at(0).toDouble();
but new error came qualified-id decalration before "=" token

jsulm

@thippu said in How to define static members in a static function in .cpp file?:

double AmpConfiguration::sampling_rate=line_list->at(0).toDouble();

Please read again what I wrote.
Where do you call this now?
It looks like you're now trying to declare a LOCAL variable with same name which is for sure not what you want to do.

thippu

@jsulm said in How to define static members in a static function in .cpp file?:

Where do you call this now?

In the mainwindow.cpp

jsulm

@thippu said in How to define static members in a static function in .cpp file?:

In the mainwindow.cpp

WHERE EXACTLY?

thippu

@jsulm
In the constructor of mainwindow.cpp
I'm calling AmpConfiguration::ReadIni(); First statement itself

jsulm

@thippu Can you actually be more precise when answering questions?
Do you mean you put that line in the constructor or inside ReadIni()?
But as I said: you're declaring a local variable with same name.
It must be like this:

AmpConfiguration::sampling_rate=line_list->at(0).toDouble();

AmpConfiguration:: can be removed as well...

thippu

@jsulm said in How to define static members in a static function in .cpp file?:

local variable

I would like it to be a global static variable.

and I would like to use it(initialize) inside AmpConfiguration::ReadIni()

@jsulm said in How to define static members in a static function in .cpp file?:

AmpConfiguration::sampling_rate=line_list->at(0).toDouble();

finally, Calling the AmpConfiguration::ReadIni()in constructor of mainwindow.cpp.

thippu

@jsulm said in How to define static members in a static function in .cpp file?:

AmpConfiguration::sampling_rate=line_list->at(0).toDouble();

No, change in the error. still, I'm getting undefined reference

jsulm

@thippu "I would like it to be a global static variable." - then why do you declare it as local variable?
Did you put

double AmpConfiguration::sampling_rate=10.2; // This has to be OUTSIDE of any method/constructor
void AmpConfiguration::ReadIni()
{
    sampling_rate=line_list->at(0).toDouble();
}

as I already wrote above?
Please read about static members in C++.

thippu

@jsulm said in How to define static members in a static function in .cpp file?:

// This has to be OUTSIDE of any method/constructor

Worked. bro
Thank you