Re: How to use hash_set [a possible solution]

Paulo da Silva <psdasilvaX@esotericaX.ptX>
Tue, 19 Jun 2007 03:42:21 +0100
Paulo da Silva escreveu:


I have a class Foo with a string. I want to store its elements in a
hash_set beeing the hash executed over the string. How do I do that?

class Foo
    string s;

hash_set<Foo> mc;
Foo mc_el("a_string_key");

What do I have to do in Foo and how do I insert mc_el in mc?


I found a possible solution. I'm posting it here for others who may need
it but also for comments from experts before I implement it in a real

So, thank you very much for any comments.
#include <memory>
#include <ext/hash_set>
#include <iostream>

using namespace std;

class Foo
    string s; // public for simplicity
    Foo(char *sc): s(sc) {}

class eqf
    bool operator()(Foo const &s1,Foo const &s2) const
    { return (s1.s==s2.s);

class hf
    size_t operator()(Foo const &x) const
    { return __gnu_cxx::hash<char const *>()(x.s.c_str());

typedef __gnu_cxx::hash_set<Foo,hf,eqf> MSet;

int main()
{ MSet mc;
    MSet::const_iterator it=mc.find(Foo("xxxx"));
    cout << "xxxx: " << (it!=mc.end()? "present":"not present")
        << endl;
    cout << "yyyy: " << (it!=mc.end()? "present":"not present")
        << endl;
    for (it=mc.begin();it!=mc.end();++it)
        cout << it->s << endl;
    return 0;

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