Kleiner-Operator zum Sortieren überladen

Jay1980

Habe es nun mal so als 'freie Funktion' versucht:

// Operator-Überladung
const s operator < ( s const& lhs, s const& rhs )
{
    if ( lhs.wert < rhs.wert ){ return lhs; }
    else { return rhs; }  
}

Fehler der kommt ist:
from main.cpp:8:
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘const _Tp& std::__median(const _Tp&, const _Tp&, const _Tp&) [with _Tp = s]’:
In file included from /usr/include/c++/4.4/algorithm:62,
/usr/include/c++/4.4/bits/stl_algo.h:2268: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:89: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__b)))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h:90: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__c)))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h:92: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__c)))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h:96: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__c)))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h:98: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__c)))’ to ‘bool’
make[2]: Verlasse Verzeichnis '/home/jay/gtd08042010/begleitend/fu-hagen/masterarbeit/h2r_bioinf/workspace-21122010/spielwiese'
make[1]: Verlasse Verzeichnis '/home/jay/gtd08042010/begleitend/fu-hagen/masterarbeit/h2r_bioinf/workspace-21122010/spielwiese'
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, _Tp) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Tp = s]’:
/usr/include/c++/4.4/bits/stl_algo.h:2268: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:2209: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)(& __pivot))))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h:2268: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:2212: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__last.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = s*, _Container = std::vector<s, std::allocator<s> >]())))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’:
/usr/include/c++/4.4/bits/stl_algo.h:2178: instantiated from ‘void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:5222: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:2106: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = s*, _Container = std::vector<s, std::allocator<s> >]())))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’:
/usr/include/c++/4.4/bits/stl_algo.h:5067: instantiated from ‘void std::partial_sort(_RAIter, _RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:2256: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:1906: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = s*, _Container = std::vector<s, std::allocator<s> >]())))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘void std::__unguarded_linear_insert(_RandomAccessIterator, _Tp) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Tp = s]’:
/usr/include/c++/4.4/bits/stl_algo.h:2112: instantiated from ‘void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:2178: instantiated from ‘void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:5222: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:2067: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__next.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = s*, _Container = std::vector<s, std::allocator<s> >]())))’ to ‘bool’
from /usr/include/c++/4.4/algorithm:62,
from main.cpp:8:
/usr/include/c++/4.4/bits/stl_heap.h: In function ‘void std::__adjust_heap(_RandomAccessIterator, _Distance, _Distance, _Tp) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Distance = int, _Tp = s]’:
In file included from /usr/include/c++/4.4/bits/stl_algo.h:62,
/usr/include/c++/4.4/bits/stl_heap.h:394: instantiated from ‘void std::make_heap(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:1904: instantiated from ‘void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:5067: instantiated from ‘void std::partial_sort(_RAIter, _RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:2256: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_heap.h:232: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator+ [with _Iterator = s*, _Container = std::vector<s, std::allocator<s> >](((const ptrdiff_t&)((const ptrdiff_t*)(&(__secondChild + -0x00000000000000001))))).__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = s*, _Container = std::vector<s, std::allocator<s> >]())))’ to ‘bool’
/usr/include/c++/4.4/bits/stl_heap.h: In function ‘void std::__push_heap(_RandomAccessIterator, _Distance, _Distance, _Tp) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Distance = int, _Tp = s]’:
/usr/include/c++/4.4/bits/stl_heap.h:244: instantiated from ‘void std::__adjust_heap(_RandomAccessIterator, _Distance, _Distance, _Tp) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Distance = int, _Tp = s]’
/usr/include/c++/4.4/bits/stl_heap.h:394: instantiated from ‘void std::make_heap(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:1904: instantiated from ‘void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:5067: instantiated from ‘void std::partial_sort(_RAIter, _RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
/usr/include/c++/4.4/bits/stl_algo.h:2256: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp instantiated from here
/usr/include/c++/4.4/bits/stl_heap.h:134: error: no match for ‘operator&&’ in ‘(__holeIndex > __topIndex) && operator<(const s&, const s&)(((const s&)((const s*)(& __value))))’
/usr/include/c++/4.4/bits/stl_heap.h:134: note: candidates are: operator&&(bool, bool) <built-in>
make[2]: *** [build/Debug/GNU-Linux-x86/main.o] Fehler 1
make[1]: *** [.build-conf] Fehler 2
make: *** [.build-impl] Fehler 2

BUILD FAILED (exit value 2, total time: 1s)

Tachyon

Vielleicht einfach bool zurückgeben?

SeppJ meint:

struct s
{
    std::string name;
    int  wert;
};
// freie Funktion operator<; -> Return Typ ist natürlich bool
bool operator< ( s const& a, s const& b ) // Bem.: a UND b sind const!
{ 
    return a.wert < b.wert;
}

SeppJ

Und die andere, technisch richtige, aber ungewöhnliche Methode wäre:

struct s
{
    string name;
    int  wert;

    bool operator< ( s const& rhs ) const // So macht man Methoden const
    {
        return ( wert < rhs.wert );
    }
};

Jay1980

Merci - etz schauen wir mal ob der Build da fluppt!

EOutOfResources

Und const -Lösung:

bool operator< (s const& rhs) const
{ 
  return this->wert < rhs.wert;
}

pumuckl

Jay1980 schrieb:

Merci - etz schauen wir mal ob der Build da fluppt!

Und danach lesen wir nochmal die Fehlermeldung und versuchen zu verstehen, was der Compiler uns mitteilen möchte:

from main.cpp:8:
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘const _Tp& std::__median(const _Tp&, const _Tp&, const _Tp&) [with _Tp = s]’:
In file included from /usr/include/c++/4.4/algorithm:62,
/usr/include/c++/4.4/bits/stl_algo.h:2268: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<s*, std::vector<s, std::allocator<s> > >]’
main.cpp:100: instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:89: error: could not convert ‘operator<(const s&, const s&)(((const s&)((const s*)__b)))’ to ‘bool’

Im Grunde genommen ist alles bis zum error: nur ein Wegweiser, wo der Fehler auftaucht, und wo er herkommt. Zeile für Zeile:

(in main.cpp, Zeile 8 hast du etwas geschrieben, was den Fehler verursacht, nämlich incirekt den Header eingebuden, an der die Stelle unmittelbar auftritt)
es wird das Funktionstemplate std::__median instantiiert, mit Templateparameter s. In dieser Funktion passiert der Fehler (Das template befindet sich in stl_algo.h)
(Diese datei wird in <algorithm> auf Zeile 62 includet)
die std::_median-Funktion wird instantiiert, weil std::__introsort_loop instantiiert wurde (Datei- und Zeilenangabe vorne, hinten die angabe welche Templateparameter)
diese Funktion wurde wiederum von std::sort instantiiert (Datei- und Zeilenangabe vorne, hinten die angabe welche Templateparameter)
diese hast du in main.cpp, Zeile 100 instantiiert
Der Fehler (der in std::__median) ist, dass der Compiler das Ergebnis eines operator<(s const&, s const&) nicht in einen bool konvertieren kann.

Das Einfachste ist immer, nach dem error: zu suchen. Dort steht das eigentliche Problem. Den ganzen Rest bräuchtest du nur, wenn du wissen willst, warum er diesen op< denn überhaupt aufruft und das Ergebnis in ein bool verwandeln möchte.

Mal was allgemeines zur Operatorüberladung: http://magazin.c-plusplus.net/artikel/�berladung von Operatoren in CPlusPlus (Teil 1)

Jay1980

Wunderbar, mein kleines Beispiel läuft, ich strauchle beim Transfer in mein 'richtiges' Programm, bei dem namespaces verwendet werden.

#include <algorithm>
#include <cstdlib>
#include <iostream>
#include <vector>

using namespace std;
namespace global {
    struct s {
        string name;
        int wert;
    };

}

// Operator-Überladung als freie Funktion
bool operator<(global::s const& lhs, global::s const& rhs) {
    return lhs.wert < rhs.wert;
}

/*
 * 
 */
int main(int argc, char** argv) {
    cout << " Start Spielwiese ... " << endl;

    vector<int> v;
    v.push_back( 2 );
    v.push_back( 3 );
    v.push_back( 1 );
    v.push_back( 5 );
    v.push_back( 6 );
    v.push_back( 4 );

    cout << "  Ausgabe der Liste:\n";
    vector<int>::const_iterator iter1 = v.begin();
    int c1 = 0;
    while (iter1 != v.end() )
    {
        cout << "   Lauf ... Item (";
        cout << c1 << "): ";
        cout << *iter1 << ";\n";
        ++iter1;
        c1++;
    }

    // Sortierung
    sort( v.begin(), v.end() );

    cout << "  Ausgabe der Liste:\n";
    vector<int>::const_iterator iter2 = v.begin();
    int c2 = 0;
    while (iter2 != v.end() )
    {
        cout << "   Lauf ... Item (";
        cout << c2 << "): ";
        cout << *iter2 << ";\n";
        ++iter2;
        c2++;
    }

    // Lauf mit Strukturen
    global::s s1;
    s1.name = "Item-Eins";
    s1.wert = 2;
    global::s s2;
    s2.name = "Item-Zwei";
    s2.wert = 3;
    global::s s3;
    s3.name = "Item-Drei";
    s3.wert = 1;

    vector<global::s> v2;
    v2.push_back( s1 );
    v2.push_back( s2 );
    v2.push_back( s3 );

    cout << "Ausgabe der Listen:\n";
    vector<global::s>::const_iterator iter3 = v2.begin();
    int c3 = 0;
    while (iter3 != v2.end())
    {
        cout << " Lauf ... Item (";
        cout << c3 << "): ";
        cout << iter3->name << " - ";
        cout << iter3->wert << ";\n";
        ++iter3;
        c3++;
    }

    // Sortierung
    sort( v2.begin(), v2.end() );

    cout << "Ausgabe der Listen:\n";
    vector<global::s>::const_iterator iter4 = v2.begin();
    int c4 = 0;
    while (iter4 != v2.end()) {
        cout << " Lauf ... Item (";
        cout << c4 << "): ";
        cout << iter4->name << " - ";
        cout << iter4->wert << ";\n";
        ++iter4;
        c4++;
    }

    cout << " ... ENDE" << endl;
    return 0;
}

Auszug aus Fehlermeldung, ich habe natürlich genau auf den ersten 'error' geachtet ... mein Überladungsversuch scheint beim Compiler nicht als solcher anzukommen:
make[1]: Verlasse Verzeichnis '/home/jay/gtd08042010/begleitend/fu-hagen/masterarbeit/h2r_bioinf/workspace-21122010/spielwiese'
from main.cpp:8:
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘const _Tp& std::__median(const _Tp&, const _Tp&, const _Tp&) [with _Tp = global::s]’:
In file included from /usr/include/c++/4.4/algorithm:62,
/usr/include/c++/4.4/bits/stl_algo.h:2268: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<global::s*, std::vector<global::s, std::allocatorglobal::s > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<global::s*, std::vector<global::s, std::allocatorglobal::s > >]’
main.cpp:98: instantiated from here
/usr/include/c++/4.4/bits/stl_algo.h:89: error: no match for ‘operator<’ in ‘__a < __b’
/usr/include/c++/4.4/bits/stl_algo.h:90: error: no match for ‘operator<’ in ‘__b < __c’
/usr/include/c++/4.4/bits/stl_algo.h:92: error: no match for ‘operator<’ in ‘__a < __c’
/usr/include/c++/4.4/bits/stl_algo.h:96: error: no match for ‘operator<’ in ‘__a < __c’
/usr/include/c++/4.4/bits/stl_algo.h:98: error: no match for ‘operator<’ in ‘__b < __c’
/usr/include/c++/4.4/bits/stl_algo.h: In function ‘_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, _Tp) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<global::s*, std::vector<global::s, std::allocatorglobal::s > >, _Tp = global::s]’:
/usr/include/c++/4.4/bits/stl_algo.h:2268: instantiated from ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<global::s*, std::vector<global::s, std::allocatorglobal::s > >, _Size = int]’
/usr/include/c++/4.4/bits/stl_algo.h:5220: instantiated from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<global::s*, std::vector<global::s, std::allocatorglobal::s > >]’
main.cpp:98: instantiated from here

CStoll

Du solltest eventuell den Vergleichsoperator in den Namensraum mit reinpacken:

namespace global { 
    struct s { 
        string name; 
        int wert; 
    }; 
    bool operator<(s const& lhs, s const& rhs) { 
        return lhs.wert < rhs.wert; 
    } 

}

(keine Sorge - der Compiler ist clever genug, den Operator dort zu finden)

SeppJ

Wenn du das wie CStoll empfiehlt machst, dann kannst du auch noch mal nach "argument dependent lookup" oder "Koenig lookup" googlen. Das ist zwar eine recht spezielle Eigenschaft von C++, aber wichtig zu wissen, wenn man mit Namespaces arbeitet.

camper

CStoll schrieb:

Du solltest eventuell den Vergleichsoperator in den Namensraum mit reinpacken:

Nicht nur eventuell. Da Überladungen für < auch im Namensraum std existieren, wird beim unqualifizierten Lookup innerhalb eines Standardalgorithmus der globale Namensraum wahrscheinlich nicht durchsucht werden. Damit bleibt nur ADNL übrig.