How to fix warning – Unbound scanf conversion. This is how I am trying to fix this:

void Class::func1(
    const string &item_as_string,
    unsigned int &unit_id,
    unsigned int &subprogam_id,
    string &slotDescription
)
{
   string bitset_flags;
   const char *line_pointer = item_as_string.c_str();
   unsigned int i, length = item_as_string.length();
   
   unit_id = 0;
   subprogram_id = 0;
   slotDescription = "";
   valid_line = false;

   boost::scoped_array<char> flags( new char[length+1] );
   flags[0]=0;

   boost::scoped_array<char> slotDescriptionPtr( new char[length+1] );
   slotDescriptionPtr[0]=0;

   int val;
   // QString pattern("%u,%u %1%s %1%s");
   val = sscanf ( line_pointer, QString("%u,%u %1%s %2%s").arg(length+1).arg(length+1).toStdString().c_str(),
                 &unit_id, &subprogram_id, flags.get(), slotDescriptionPtr.get() );
}

I need help in this line of code :

val = sscanf ( line_pointer, QString("%u,%u %1%s %2%s").arg(length+1).arg(length+1).toStdString().c_str(),
                 &unit_id, &subprogram_id, flags.get(), slotDescriptionPtr.get() );