Insert into multimap causes segfault - c++

Question

I am working on a project using multimaps inside of my own class, and I have run into a segfault. Here are the parts of my code relating to the issue. I would really appreciate some help. Thanks.
Here is database.h
#include <iostream>
#include <map>
using namespace std;
class database{
public:
database(); // start up the database
int update(string,int); // update it
bool is_word(string); //advises if the word is a word
double prox_mean(string); // finds the average prox
private:
multimap<string,int> *data; // must be pointer
protected:
};
Here is the database.cpp
#include <iostream>
#include <string>
#include <map>
#include <utility>
#include "database.h"
using namespace std;
// start with the constructor
database::database()
{
data = new multimap<string,int>; // allocates new space for the database
}
int database::update(string word,int prox)
{
// add another instance of the word to the database
cout << "test1"<<endl;
data->insert( pair<string,int>(word,prox));
cout << "test2" <<endl;
// need to be able to tell if it is a word
bool isWord = database::is_word(word);
// find the average proximity
double ave = database::prox_mean(word);
// tells the gui to updata
// gui::update(word,ave,isWord); // not finished yet
return 0;
}
Here is test.cpp
#include <iostream>
#include <string>
#include <map>
#include "database.h" //this is my file
using namespace std;
int main()
{
// first test the constructor
database * data;
data->update("trail",3);
data->update("mix",2);
data->update("nut",7);
data->update("and",8);
data->update("trail",8);
data->update("and",3);
data->update("candy",8);
// cout<< (int) data->size()<<endl;
return 0;
}
Thanks very much. It compiles and runs up to cout << "test1" << endl; but segfaults on the next line.
Rusty

Answer 1

You never actually created a database object, just a pointer to nowhere (perhaps you're used to another language).
Try creating one like this database data;
And then change your -> to . to access the members.
Consider obtaining one of the books at The Definitive C++ Book Guide and List as well.

Answer 2

You need to allocate your database before starting to insert data on it.
Change:
database *data;
to:
database *data = new database();
or:
database data;
in main().
EDIT: if you use the latter, change -> to . on the subsequent method calls. Otherwise, remember to delete your data object after using it.