class operator overloading error

jericho63

Hello everybody,

I try to rewrite c++ Builder project to qt and i have a problem with the operator overloading in a class (i think it's that but not sure).

here my class definition

class cSoldierd
{
public:
    friend int  operator < ( const cSoldierd &s1, const cSoldierd &s2 )
    {
        return ( (s1.nom+"|"+s1.prenom+"|"+s1.initiale+"|"+s1.initiale2+"|"+s1.suffixe) < (s2.nom+"|"+s2.prenom+"|"+s2.initiale+"|"+s2.initiale2+"|"+s2.suffixe) );
    };
    friend bool operator == (  const cSoldierd &s1 , const cSoldierd &s2   )
    {
        return ((s2.nom+"|"+s2.prenom+"|"+s2.initiale+"|"+s2.initiale2+"|"+s2.suffixe) == (s1.nom+"|"+s1.prenom+"|"+s1.initiale+"|"+s1.initiale2+"|"+s1.suffixe));
    };

    QString id;
    QString nom;
    QString prenom;
    QString initiale;
    QString initiale2;
    QString suffixe;
    QString unit;
    QString sunit;
    QString asn;

    QString ligne()
    {
        return id+"-"+nom+"-"+prenom+"-"+initiale+"-"+initiale2+"-"+suffixe+"-"+unit+"-"+sunit+"-"+asn;

    }
    int nb;

};

I store object in a Qset, like this :

cSoldierd temp;
    temp.asn = "123456789";
    temp.nom = "toto";
    temp.prenom = "titi";
    temp.initiale = "t";
    temp.initiale2 = "y";
    temp.suffixe = "jr";
    temp.unit = "137th";
    temp.id =  "1";
    temp.sunit = "co c";
    temp.nb = 1;


    QSet<cSoldierd> scSoldierd;
    scSoldierd.insert(temp);

but i have this error :

C:\Qt\5.12.12\mingw73_64\include\QtCore\qhashfunctions.h:118: erreur : no matching function for call to 'qHash(const cSoldierd&)'
                                           ^

Christian Ehrlicher

@jericho63 said in class operator overloarding error:

function for call to 'qHash(const cSoldierd&)'

So where did you define this function?

Pl45m4

@jericho63 said in class operator overloarding error:

QSet<cSoldierd> scSoldierd;

If you look at the documentation of QSet you can read:

QSet<T> is one of Qt's generic container classes. It stores values in an unspecified order and provides very fast lookup of the values. Internally, QSet<T> is implemented as a QHash.

https://doc.qt.io/qt-6/qset.html#details

And because it's unknown to Qt how to "hash" a type cSoldierd, you get this error.
So, as @Christian-Ehrlicher said, you need to define for your custom class, what to hash.

An example is shown in QHash documentation:

#ifndef EMPLOYEE_H
#define EMPLOYEE_H

class Employee
{
public:
    Employee() {}
    Employee(const QString &name, QDate dateOfBirth);
    ...

private:
    QString myName;
    QDate myDateOfBirth;
};

inline bool operator==(const Employee &e1, const Employee &e2)
{
    return e1.name() == e2.name()
           && e1.dateOfBirth() == e2.dateOfBirth();
}

inline size_t qHash(const Employee &key, size_t seed)
{
    return qHashMulti(seed, key.name(), key.dateOfBirth());
}

#endif // EMPLOYEE_H

Also:

Note: In Qt 6 it is possible to define a qHash() overload taking only one argument; support for this is deprecated. Starting with Qt 7, it will be mandatory to use a two-arguments overload. If both a one-argument and a two-arguments overload are defined for a key type, the latter is used by QHash (note that you can simply define a two-arguments version, and use a default value for the seed parameter).

https://doc.qt.io/qt-6/qhash.html#the-hashing-function

jericho63

This post is deleted!

Pl45m4

@jericho63 said in class operator overloading error:

erreur : type 'const QString' does not provide a call operator

This says it all.
In the example the members are private and therefore access functions are used to retrieve the value, which you don't have.
Your nom and prenom are just (public) strings in your class, while key.name(), as used in the example, is the get function to return the private class member.
Make your members private and write get functions or remove the (), so that it's not a function call anymore.

jericho63

thank , this is a long time i have no made code.
I remember it now.
i have also this error

'qHashMulti' was not declared in this scope

this error mean, i need an .h file, but i find a QMultiHash only.

I don't understand

Pl45m4

@jericho63

Do you use Qt6 or Qt5?

Found out that the qHashMulti expression is only available in Qt6.0.0 and later.

https://doc.qt.io/qt-6/qhash.html#qHashMulti

I guess you have to pick another qHash function from one of those, if you use Qt5:

https://doc.qt.io/qt-5/qhash.html#related-non-members

jericho63

@Pl45m4

i use qt6.6

Pl45m4

@jericho63

Then including QHash or QMultiHash should fix this.

jericho63

@Pl45m4
hello

ok, no morre error at the class side declaration but another one yet when i insert objet un Qset

            cSoldierd temp;
            temp.asn = query3.value(5).toString();
            temp.nom = query3.value(1).toString();
            temp.prenom = query3.value(2).toString();
            temp.initiale = query3.value(3).toString();
            temp.initiale2 = query3.value(4).toString();
            temp.suffixe = query3.value(6).toString();
            temp.unit = query3.value(7).toString();
            temp.id =  query3.value(0).toString();
            temp.sunit = query3.value(8).toString();
            temp.nb = 1;
            scSoldierd.insert(temp);

C:\Users\john MIller\Documents\Gest_base\mainwindow.cpp:243: erreur : static assertion failed: The key type must have a qHash overload or a std::hash specialization

jsulm

@jericho63 So, is there a qHash overload for the key type?

jericho63

@jsulm

I suppose not, but how i do this?
I have reread the doc, i haven't find an example.

class cSoldierd
    {
    public:
        friend int  operator < ( const cSoldierd &s1, const cSoldierd &s2 )
        {
            return ( (s1.nom+"|"+s1.prenom+"|"+s1.initiale+"|"+s1.initiale2+"|"+s1.suffixe) < (s2.nom+"|"+s2.prenom+"|"+s2.initiale+"|"+s2.initiale2+"|"+s2.suffixe) );
        };
        friend bool operator == (  const cSoldierd &s1 , const cSoldierd &s2   )
        {
            return ((s2.nom+"|"+s2.prenom+"|"+s2.initiale+"|"+s2.initiale2+"|"+s2.suffixe) == (s1.nom+"|"+s1.prenom+"|"+s1.initiale+"|"+s1.initiale2+"|"+s1.suffixe));
        };
    
        inline size_t qHash(const cSoldierd &key, size_t seed)
        {
            return qHashMulti (seed, key.nom,key.prenom,key.initiale,key.initiale2,key.suffixe);
    
        }
        
    
        QString id;
        QString nom;
        QString prenom;
        QString initiale;
        QString initiale2;
        QString suffixe;
        QString unit;
        QString sunit;
        QString asn;
    
        QString ligne()
        {
            return id+"-"+nom+"-"+prenom+"-"+initiale+"-"+initiale2+"-"+suffixe+"-"+unit+"-"+sunit+"-"+asn;
    
        }
        int nb;
    
    };

jsulm

@jericho63 said in class operator overloading error:

but how i do this?

By defining size_t qHash(const cSoldierd &key, size_t seed) outside of the class, not as class member. Same for the other operators in your code (there is also no need to use keyword "friend" for methods).

jericho63

@jsulm

ok, i have deplace size_t qHash(const cSoldierd &key, size_t seed) and the operator outside the class like thos :

class cSoldierd
{
public:



    QString id;
    QString nom;
    QString prenom;
    QString initiale;
    QString initiale2;
    QString suffixe;
    QString unit;
    QString sunit;
    QString asn;

    QString ligne()
    {
        return id+"-"+nom+"-"+prenom+"-"+initiale+"-"+initiale2+"-"+suffixe+"-"+unit+"-"+sunit+"-"+asn;

    }
    int nb;

};
inline size_t qHash(const cSoldierd &key, size_t seed)
{
    return qHashMulti (seed, key.nom,key.prenom,key.initiale,key.initiale2,key.suffixe);

}
int  operator < ( const cSoldierd &s1, const cSoldierd &s2 )
{
    return ( (s1.nom+"|"+s1.prenom+"|"+s1.initiale+"|"+s1.initiale2+"|"+s1.suffixe) < (s2.nom+"|"+s2.prenom+"|"+s2.initiale+"|"+s2.initiale2+"|"+s2.suffixe) );
};
bool operator == (  const cSoldierd &s1 , const cSoldierd &s2   )
{
    return ((s2.nom+"|"+s2.prenom+"|"+s2.initiale+"|"+s2.initiale2+"|"+s2.suffixe) == (s1.nom+"|"+s1.prenom+"|"+s1.initiale+"|"+s1.initiale2+"|"+s1.suffixe));
};

but now i have more errors:

:-1: erreur : CMakeFiles/Gest_base.dir/main.cpp.obj: in function `bool std::__constant_string_p<char>(char const*)':

\mainwindow.h:52: erreur : multiple definition of `operator<(cSoldierd const&, cSoldierd const&)'; CMakeFiles/Gest_base.dir/Gest_base_autogen/mocs_compilation.cpp.obj:mainwindow.h:52: first defined here

i don't understand the second error, i have only one definition for each operator

Christian Ehrlicher

You must define them inline

jericho63

@jericho63

that's work!
Thank you
The operator overload no longer need to be define in a class now?