what is keyword i have to use instead snprintf in qt ?

Qt embedded developer

I want to implement below function in qt . so i need guide regarding which function of qt i need to choose instead snprintf, printf and exit(1) ?

 static char filename[20];
  static int adapter_nr = 2;

  snprintf (filename, 19, "/dev/i2c-%d", adapter_nr);
  filehandle = open(filename,O_RDWR);
  if (filehandle < 0) {
    printf ("Error : Can't open /dev/i2c-%d\n",adapter_nr);
    /* ERROR HANDLING; you can check errno to see what went wrong */
    exit(1);
  }

  return 0;

jsulm

@Qt-embedded-developer

printf - std::cout
exit - https://doc.qt.io/qt-5/qcoreapplication.html#exit
snprintf - see all the QString::arg methods like https://doc.qt.io/qt-5/qstring.html#arg
File handling - QFile

mrjj

Hi

instead snprintf, printf and exit(1) ?

snprintf = QStrings arg. https://doc.qt.io/qt-5/qstring.html#arg
printf = You can still use it if you want. but printing to console in a GUI app is mostly for logging.
For user feed back, you can use https://doc.qt.io/qt-5/qmessagebox.html
TO show info to the end user.
exit(1); will still work and terminate the app. You might not want to do that for a GUI program and rather
display info to user.

jsulm

@Qt-embedded-developer

printf - std::cout
exit - https://doc.qt.io/qt-5/qcoreapplication.html#exit
snprintf - see all the QString::arg methods like https://doc.qt.io/qt-5/qstring.html#arg
File handling - QFile

Qt embedded developer

@mrjj Yes i might not want to use exit for an gui program. so i have to use return some value other than 0 to indicate this function failed.

i heard that snprintf stop crash if more than 20 character i write into filename array . will same thing possible with QStrings arg ?

mrjj

Hi

@mrjj Yes i might not want to use exit for an gui program. so i have to use return some value other than 0 to indicate this function failed.

I think you dont want to use exit at all but simply return the error code, from errno - maybe so the calling function can know it went wrong.

i heard that snprintf stop crash if more than 20 character i write into filename array . will same thing possible with QStrings arg ?
Well your buffer is filename[20]; so you can overflow it.

With QString there is no such buffer directly so most likely it won't be an issue as paths won't be that long anyway.

jsulm

@Qt-embedded-developer said in what is keyword i have to use instead snprintf in qt ?:

i heard that snprintf stop crash if more than 20 character

Do you mean it crashes with < 20 characters?! Where did you here that and which implementation was it? I never heard about QString::arg crashing, so just use it (you can also write tests for your use cases to make sure it isn't crashing).

Qt embedded developer

@jsulm i am telling "more than 20 " means not <20 . its >20.

snprintf in c

jsulm

@Qt-embedded-developer Well, you wrote: "i heard that snprintf stop crash if more than 20 character"...

Qt embedded developer

@jsulm Sorry for not write clearly. when i write more than 20 characters using sprintf then it make crash program in c. so to avoid that situation. in c for safe side to avoid crash we use snprintf.

JonB

@Qt-embedded-developer
I think it most unlikely that an implementation of snprintf() will "crash" (or go wrong) if more than 20 characters, and I don't know where you think you have heard this. It would have been reported. So

 static char filename[20];
snprintf (filename, 20, "/dev/i2c-%d", adapter_nr);

should be fine.

However this doesn't matter if you use QString methods anyway.