Arduino/c++ using SoftwareSerial class in another class

I'm trying to build some class, it's been a very long time since i've been making OOP, and mostly i've forgot everything ;)

I'm trying to build class inside of wich i read from SoftwareSerial, and make something with that later.

I've made this code:

    #include <SoftwareSerial.h>

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

class pH
{
  int Stable;
  unsigned long previousMillis;
  long Gap;
  //SoftwareSerial pHrs(100,100);
  //SoftwareSerial portOne(100, 100);
  //SoftwareSerial pHrs = new SoftwareSerial(90,90);
  SoftwareSerial SerialPort;

  // Constructor - creates a pH
  // and initializes the member variables and state
  public: pH(uint8_t tx, uint8_t rx, long pHgap)
  {
    Gap = pHgap;
    //SerialPort(rx, tx);
  }

};

But get this:

    /home/san/Projekty/pHmetr/rs8/rs8.ino: In constructor 'pH::pH(uint8_t, uint8_t, long int)':
rs8:26: error: no matching function for call to 'SoftwareSerial::SoftwareSerial()'
   {
   ^
/home/san/Projekty/pHmetr/rs8/rs8.ino:26:3: note: candidates are:
In file included from /home/san/Projekty/pHmetr/rs8/rs8.ino:1:0:
/home/san/.local/share/umake/ide/arduino/hardware/arduino/avr/libraries/SoftwareSerial/SoftwareSerial.h:89:3: note: SoftwareSerial::SoftwareSerial(uint8_t, uint8_t, bool)
   SoftwareSerial(uint8_t receivePin, uint8_t transmitPin, bool inverse_logic = false);

   ^
/home/san/.local/share/umake/ide/arduino/hardware/arduino/avr/libraries/SoftwareSerial/SoftwareSerial.h:89:3: note:   candidate expects 3 arguments, 0 provided
/home/san/.local/share/umake/ide/arduino/hardware/arduino/avr/libraries/SoftwareSerial/SoftwareSerial.h:47:7: note: constexpr SoftwareSerial::SoftwareSerial(const SoftwareSerial&)
 class SoftwareSerial : public Stream

       ^
/home/san/.local/share/umake/ide/arduino/hardware/arduino/avr/libraries/SoftwareSerial/SoftwareSerial.h:47:7: note:   candidate expects 1 argument, 0 provided
exit status 1
no matching function for call to 'SoftwareSerial::SoftwareSerial()'

I've tried to find solution myself, but somehow i'm getting lost...

Best Regadrs!

class pH
{
  int Stable;
  unsigned long previousMillis;
  long Gap;
  //SoftwareSerial pHrs(100,100);
  //SoftwareSerial portOne(100, 100);
  //SoftwareSerial pHrs = new SoftwareSerial(90,90);
  SoftwareSerial SerialPort;

  // Constructor - creates a pH
  // and initializes the member variables and state
  public: 
    pH(uint8_t tx, uint8_t rx, long pHgap)
      : SoftwareSerial(/* You should initalize your base class */) // <---
    {
      Gap = pHgap;
      //SerialPort(rx, tx);
    }
};

You should initialize your base class in your constructor.