Bonjour,
constatant que les algo utilise souvent la fonction swap. J'ai essayer de jouer avec pour optimiser un sort.
Voici le code :
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#include <algorithm>
#include <iostream>
#include <vector>
#include <string>
 
//class qui contient la fonction swap pour éviter des recopie de memoire
class A 
{
public :
	A(int a,std::string s) :myString(s),nb(a){ };
 
	const std::string &GetString() {return myString;}
	bool operator<(const A& a) {return nb<a.nb;}
	A&  operator=(const A& a) 
		{
		static int nbegale(0);
		std::cout<<"= : "<<++nbegale<<std::endl;
		nb<a.nb;
		myString=a.myString;
		return (*this);
		}
	void swap(A& a) 
		{
			static int nbswap(0);
			std::cout<<"swap : "<<++nbswap<<std::endl;
			std::swap(nb,a.nb);
			myString.swap(a.myString);
		};
private:
	std::string myString;
	int nb;
 
};
//specialisation de la fonction swap pour la class A
template<>
inline void std::swap<A> ( A& a, A& b )
{
	a.swap(b);
};
 
int main(int argc, char** argv)
{
	//mon vecteur a trier
	std::vector<A> vect;
       //on remplie de n'importe quoi
      //le but etant quil y en ai assez pour que swap soit appelé
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(2,"deux"));
	vect.push_back(A(15,"quinze"));
	vect.push_back(A(10,"dix"));
	vect.push_back(A(5,"cinq"));
	vect.push_back(A(1,"un"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(30,"trente"));
	vect.push_back(A(30,"trente"));
 
     //on fait le trie
	std::sort(vect.begin(),vect.end());
return 0;
}
En prenant l'hypothèse qu'un égale dure 1 second (du au reallocation et recopie de memoire), et swap .5s (echange de la mémoire, donc peut de recopie)

Les résultats que j'obtiens sous visual 20005 sont :
- sans le swap : 234 operation egale = 234s
- avec le swap : 74 operation swap et 72 operation egale = 109 s

Ce qui n'est pas négligable.
Maintenant je me demandé si :
1- ce que j'ai fait est tout à fait correcte
2- il n'y as pas d'autre manière de faire
3- on est obligé de spécifier std::swap

[EDIT]
4- existe t'il d'autre astuce comme celle la???
merci