[Solved]Connecting to a serial device

Alfredo Palhares

Hello everyone,

I am new to Qt and C++ and programming in general. I am trying to connect to serial device, here is the code:

#include <QApplication>
#include <QPushButton>
#include <QtSerialPort/QtSerialPort>

int main(int argc, char **argv)
{
  QApplication app (argc, argv);

  //QPushButton button("Hello world !");
  //button.show();


  std::string portName = "/dev/ttyUSB0";
  int baudRate = 115200;

  bool parity = true;
/*
 * We're trying to send this
 * 0000 0000 0000 0000 0000 0000 0000 00aa
 * 0000 0202 cc00 0000 0000 0000 0000 0000
 * 0a                                       .
 */

  QSerialPort serial;

  serial->setPortName(portName);
  serial->setBaudRate(baudRate);
  serial->setParity(parity);


  return app.exec();
}

And while building I get this:

INFO: There is a new version of biicode. Download it at https://www.biicode.com/downloads
INFO: Processing changes...
Building: "cmake" --build . 
Scanning dependencies of target user_yats_main
[100%] Building CXX object user_yats/CMakeFiles/user_yats_main.dir/main.cpp.o
/path/to/my/repomain.cpp: In function ‘int main(int, char**)’:
/path/to/my/repomain.cpp:26:9: error: base operand of ‘->’ has non-pointer type ‘QSerialPort’
   serial->setPortName(portName);
         ^
/path/to/my/repomain.cpp:27:9: error: base operand of ‘->’ has non-pointer type ‘QSerialPort’
   serial->setBaudRate(baudRate);
         ^
/path/to/my/repomain.cpp:28:9: error: base operand of ‘->’ has non-pointer type ‘QSerialPort’
   serial->setParity(parity);
         ^
user_yats/CMakeFiles/user_yats_main.dir/build.make:57: recipe for target 'user_yats/CMakeFiles/user_yats_main.dir/main.cpp.o' failed
make[2]: *** [user_yats/CMakeFiles/user_yats_main.dir/main.cpp.o] Error 1
CMakeFiles/Makefile2:106: recipe for target 'user_yats/CMakeFiles/user_yats_main.dir/all' failed
make[1]: *** [user_yats/CMakeFiles/user_yats_main.dir/all] Error 2
Makefile:85: recipe for target 'all' failed
make: *** [all] Error 2

What am I doing wrong ?

mcosta

Hi and welcome to devnet,

I don't know if is related but since Qt 5.1 you can use QSerialPort.

BTW the error is here

QSerialPort serial;

serial->setPortName(portName);
serial->setBaudRate(baudRate);
serial->setParity(parity);

You have to write

QSerialPort serial;

serial.setPortName(portName);
serial.setBaudRate(baudRate);
serial.setParity(parity);

Alfredo Palhares

QSerialPort *serial;

Instancing QSerialPort as a pointer works, why is this ?

Alfredo Palhares

Hello @mcosta thank you for your quick reply !

What is the difference between -> and .set when using class methods on C++ ?
And do you know why the -> works if I instance the QSerialPort as a pointer ?

mcosta

Hi,

in C++ you have to use . with objects and references and -> with pointers.
Remember that to create an object in the heap (using pointers) you have to use the new operator

QSerialPort *serial = new QSerialPort;

serial->setPortNumber(port);
....

*NOTE If you have this kind of doubt about the C++ language I suggest to study deeper it before go ahead with complex programs