I would like to see a hash_map example in C++

Question

I don\'t know how to use the hash function in C++, but I know that we can use hash_map. Does g++ support that by simply including #include

Answer 1

The current C++ standard does not have hash maps, but the coming C++0x standard does, and these are already supported by g++ in the shape of "unordered maps":

#include 
#include 
#include 
using namespace std;

int main() {
    unordered_map  m;
    m["foo"] = 42;
    cout << m["foo"] << endl;
}

In order to get this compile, you need to tell g++ that you are using C++0x:

g++ -std=c++0x main.cpp

These maps work pretty much as std::map does, except that instead of providing a custom operator<() for your own types, you need to provide a custom hash function - suitable functions are provided for types like integers and strings.