hash_map

gecoool · 12-21-2005, 06:24 AM

please help. i want to insert some elements in a hash map like this:

#include <iostream>
#include <ext/hash_map>
#include <functional>

using namespace __gnu_cxx;
using namespace std;

typedef hash_map< string, int, hash<string>, equal_to<string> > map_type;
int main()
{
map_type m;
string kk = "mykey";
int vv = 2;
m[kk] = vv; // <= error here ...
return 0;
}

the code above doesn't even compile. What am I doing wrong here ? please advice me.

YetAnotherDave · 12-21-2005, 12:11 PM

The reason the code does not compile as is is that the hash<> template is fairly limited and will not apply to the std::string type. The following code includes a string hasher that fixes the compile problem.

Code:

#include <iostream>
#include <ext/hash_map>
#include <functional>

using namespace __gnu_cxx;
using namespace std;

struct hashstr
{
    size_t operator()(const string& s) const
    {
        hash<const char*> H;
        return H(s.c_str());
    }
};


typedef hash_map< string, int, hashstr, equal_to<string> > map_type;
int main()
{
    map_type m;
    string kk = "mykey";
    int vv = 2;
    m[kk] = vv; // <= error here ...
    return 0;
}

gecoool · 01-08-2006, 05:34 AM

Thx YetAnotherDave. It worked !