How to append struct to QList?

pauledd

Hi
Is there a more elegant way to append a custom struct data type to a QList?
Lets say I have this custom struct and declared QList of that same type:

struct Blood{
	QDateTime dateTime;
	unsigned int systole;
	unsigned int diastole;
	unsigned int puls;
};
...
private:
	QList<Blood> readDataList;

Now I want to append new values to the list (by going through a SQL source), I did this:

Blood tempValue;
while (query.next()) {
			tempValue.dateTime = QDateTime::fromString(query.value(0).toString(), "dd.MM.yyyy-hh:mm");
			tempValue.systole = query.value(1).toInt();
			tempValue.diastole = query.value(2).toInt();
			tempValue.puls = query.value(3).toInt();
			readDataList.append(tempValue);
		}

this works, but is there a shorter way doing this? Something like this in one line without tempValue?:

readDataList.append(Blood(QDateTime::fromString(query.value(0).toString(), "dd.MM.yyyy-hh:mm") ,query.value(1).toInt(),query.value(2).toInt(),query.value(3).toInt());

raven-worx

@pauledd said in How to append struct to QList?:
Basically you can see a struct as a class (just with different default visibility).
So you are able to add methods and also a constructor to the struct.

struct Blood{
        Blood(QDateTime dt, unsigned int s, unsigned int d, unsigned int p)
             : dateTime(dt), systole(s), diastole(d), puls(p)
        {
        }

	QDateTime dateTime;
	unsigned int systole;
	unsigned int diastole;
	unsigned int puls;
};
....
readDataList << Blood(QDateTime::fromString(query.value(0).toString(), "dd.MM.yyyy-hh:mm") ,query.value(1).toInt(),query.value(2).toInt(),query.value(3).toInt();

VRonin

Your class should be assignable to go in a QList:

To qualify, a type must provide a default constructor, a copy constructor, and an assignment operator.

I think in your case they are created by the compiler but it probably is a good idea to make them explicit together with a
Blood(const QDateTime& dt, unsigned int s, unsigned int d, unsigned int p) constructor as suggested above

pauledd

Thank you both! It works.
@VRonin and why you only use const & with the QDateTime and not with the int's too?

VRonin

@pauledd said in How to append struct to QList?:

@VRonin and why you only use const & with the QDateTime and not with the int's too?

My general rule is: if the data is greater than 64 bits, pass it by const reference.

QDateTime might be borderline as inside it probably just contains a quint64 but I pass it by const reference to be safe, the ints are (normally) 32 bits so they can go by value with no expense

raven-worx

@pauledd said in How to append struct to QList?:

why you only use const & with the QDateTime and not with the int's too?

because you wont gain any/much benefit (efficiency) from it. With the const reference you save one copy instruction.

pauledd

Thanks a lot! Marked as solved.

pauledd

Just one more question arose

@VRonin said in How to append struct to QList?:

To qualify, a type must provide a ... and an assignment operator.

Does the assignment operator look correct? (it compiles fine):

struct Blood{
	Blood(const QDateTime& dt, unsigned int s, unsigned int d, unsigned int p)
		:dateTime(dt),systole(s),diastole(d),puls(p){}
	Blood(){}
	
	QDateTime dateTime;
	unsigned int systole;
	unsigned int diastole;
	unsigned int puls;
	
	friend QDataStream &operator<<(QDataStream &out, const Blood& blood){
		out << blood.dateTime << blood.systole << blood.diastole << blood.puls;
		return out;
	}
};

VRonin

That's not an assignment operator. see http://www.cplusplus.com/doc/tutorial/classes2/#copy_assignment

class Blood{
public:
	Blood(const QDateTime& dt, unsigned int s, unsigned int d, unsigned int p)
		:dateTime(dt),systole(s),diastole(d),puls(p){}
	Blood() {} //Default constructor
Blood(const Blood& other)
:dateTime(other.dateTime ),systole(other.systole),diastole(other.diastole),puls(other.puls){} // Copy constructor
	Blood& operator=(const Blood& other){
dateTime = other.dateTime ;
systole=other.systole;
diastole=other.diastole;
puls=other.puls;
return *this;
} //assingment operator

// encapsulate members
const QDateTime& dateTime() const { return dateTime;}
void setDateTime(const QDateTime& val){dateTime=val;}
unsigned int systole() const { return systole;}
void setSystole(unsigned int val){systole=val;}
unsigned int diastole() const { return diastole;}
void setDiastole(unsigned int val){diastole=val;}
unsigned int puls() const { return puls;}
void setPuls(unsigned int val){puls=val;}

private:
	QDateTime dateTime;
	unsigned int systole;
	unsigned int diastole;
	unsigned int puls;
	
};

pauledd

Ok thanks, thats looks like I'll spend ages puzzling over this exercise.

pauledd

More questions :(

My little nice struct exploded to a huge class ;) that makes me considering to use my very first approach again.

I just short read about assignment operator and in your assignment operator declaration shouldn't there also be a self-assigned test like this?

...
if (this == &other) return *this;
...

If I try your class I get a load of errors about previous declarations:
alt text


In file included from ../test1/blood.cpp:1:0:
../test1/blood.h:31:12: error: 'QDateTime Blood::dateTime' conflicts with a previous declaration
  QDateTime dateTime;
            ^
../test1/blood.h:21:18: note: previous declaration 'const QDateTime& Blood::dateTime() const'
 const QDateTime& dateTime() const { return dateTime;}
                  ^
../test1/blood.h:32:15: error: 'unsigned int Blood::systole' conflicts with a previous declaration
  unsigned int systole;
               ^
../test1/blood.h:23:14: note: previous declaration 'unsigned int Blood::systole() const'
 unsigned int systole() const { return systole;}
              ^
../test1/blood.h:33:15: error: 'unsigned int Blood::diastole' conflicts with a previous declaration
  unsigned int diastole;
               ^
../test1/blood.h:25:14: note: previous declaration 'unsigned int Blood::diastole() const'
 unsigned int diastole() const { return diastole;}
              ^
../test1/blood.h:34:15: error: 'unsigned int Blood::puls' conflicts with a previous declaration
  unsigned int puls;
               ^
../test1/blood.h:27:14: note: previous declaration 'unsigned int Blood::puls() const'
 unsigned int puls() const { return puls;}
              ^
../test1/blood.h: In constructor 'Blood::Blood(const QDateTime&, unsigned int, unsigned int, unsigned int)':
../test1/blood.h:8:4: error: class 'Blood' does not have any field named 'dateTime'
   :dateTime(dt),systole(s),diastole(d),puls(p){}
    ^
../test1/blood.h:8:17: error: class 'Blood' does not have any field named 'systole'
   :dateTime(dt),systole(s),diastole(d),puls(p){}
                 ^
../test1/blood.h:8:28: error: class 'Blood' does not have any field named 'diastole'
   :dateTime(dt),systole(s),diastole(d),puls(p){}
                            ^
../test1/blood.h:8:40: error: class 'Blood' does not have any field named 'puls'
   :dateTime(dt),systole(s),diastole(d),puls(p){}
                                        ^
../test1/blood.h: In copy constructor 'Blood::Blood(const Blood&)':
../test1/blood.h:11:2: error: class 'Blood' does not have any field named 'dateTime'
 :dateTime(other.dateTime ),systole(other.systole),diastole(other.diastole),puls(other.puls){} // Copy constructor
  ^
../test1/blood.h:11:28: error: class 'Blood' does not have any field named 'systole'
 :dateTime(other.dateTime ),systole(other.systole),diastole(other.diastole),puls(other.puls){} // Copy constructor
                            ^
../test1/blood.h:11:51: error: class 'Blood' does not have any field named 'diastole'
 :dateTime(other.dateTime ),systole(other.systole),diastole(other.diastole),puls(other.puls){} // Copy constructor
                                                   ^
../test1/blood.h:11:76: error: class 'Blood' does not have any field named 'puls'
 :dateTime(other.dateTime ),systole(other.systole),diastole(other.diastole),puls(other.puls){} // Copy constructor
                                                                            ^
../test1/blood.h: In member function 'Blood& Blood::operator=(const Blood&)':
../test1/blood.h:13:10: error: invalid use of member function (did you forget the '()' ?)
 dateTime = other.dateTime ;
          ^
../test1/blood.h:14:8: error: invalid use of member function (did you forget the '()' ?)
 systole=other.systole;
        ^
../test1/blood.h:15:9: error: invalid use of member function (did you forget the '()' ?)
 diastole=other.diastole;
         ^
../test1/blood.h:16:5: error: invalid use of member function (did you forget the '()' ?)
 puls=other.puls;
     ^
../test1/blood.h: In member function 'const QDateTime& Blood::dateTime() const':
../test1/blood.h:21:44: error: invalid initialization of reference of type 'const QDateTime&' from expression of type '<unresolved overloaded function type>'
 const QDateTime& dateTime() const { return dateTime;}
                                            ^
../test1/blood.h: In member function 'void Blood::setDateTime(const QDateTime&)':
../test1/blood.h:22:48: error: invalid use of member function (did you forget the '()' ?)
 void setDateTime(const QDateTime& val){dateTime=val;}
                                                ^
../test1/blood.h: In member function 'unsigned int Blood::systole() const':
../test1/blood.h:23:39: error: cannot convert 'Blood::systole' from type 'unsigned int (Blood::)() const' to type 'unsigned int'
 unsigned int systole() const { return systole;}
                                       ^
../test1/blood.h: In member function 'void Blood::setSystole(unsigned int)':
../test1/blood.h:24:42: error: invalid use of member function (did you forget the '()' ?)
 void setSystole(unsigned int val){systole=val;}
                                          ^
../test1/blood.h: In member function 'unsigned int Blood::diastole() const':
../test1/blood.h:25:40: error: cannot convert 'Blood::diastole' from type 'unsigned int (Blood::)() const' to type 'unsigned int'
 unsigned int diastole() const { return diastole;}
                                        ^
../test1/blood.h: In member function 'void Blood::setDiastole(unsigned int)':
../test1/blood.h:26:44: error: invalid use of member function (did you forget the '()' ?)
 void setDiastole(unsigned int val){diastole=val;}
                                            ^
../test1/blood.h: In member function 'unsigned int Blood::puls() const':
../test1/blood.h:27:36: error: cannot convert 'Blood::puls' from type 'unsigned int (Blood::)() const' to type 'unsigned int'
 unsigned int puls() const { return puls;}
                                    ^
../test1/blood.h: In member function 'void Blood::setPuls(unsigned int)':
../test1/blood.h:28:36: error: invalid use of member function (did you forget the '()' ?)
 void setPuls(unsigned int val){puls=val;}
                                    ^
../test1/blood.cpp: At global scope:
../test1/blood.cpp:3:1: error: redefinition of 'Blood::Blood()'
 Blood::Blood()
 ^
In file included from ../test1/blood.cpp:1:0:
../test1/blood.h:9:2: note: 'Blood::Blood()' previously defined here
  Blood() {} //Default constructor
  ^
Makefile:885: recipe for target 'blood.o' failed

kshegunov

@pauledd said in How to append struct to QList?:

If I try your class I get a load of errors about previous declarations:

You should resolve the errors, it's a trivial typo (conflicting function and member names):

class Blood
{
public:
    // ...
    QDateTime dateTime() const;
    void setDateTime(const QDateTime &);
    //...

private:
    DateTime _dateTime; //< Rename so it doesn't conflict with the method name
    // ...	
};

//< Good practice is to be explicit about inlined methods and makes for a lighter reading
//< Also my advice is to return by value, not const references
inline QDateTime Blood::dateTime() const 
{
    return _dateTime;
}

inline void Blood::setDateTime(const QDateTime & val)
{
    _dateTime = val;
}

pauledd

Thank you for the hints, I think I now have enough information to solve it.