Iterator Question

Hello Everyone,
I would like to return a pointer to an object that is found in a set. Here is the code:

Code:

---

#include <cstdlib>
#include <iostream>
#include <string>
#include <set>

using namespace std;

class KeyValue
{
public:
    KeyValue(string key, string value) : _key(key), _value(value) {

    }

    string getName() const { return this-> _key; }

    string getValue() const { return this-> _value; }

    bool operator==(const KeyValue& other) const
    {
        return (this->_key == other.getName());
    }

    bool operator<(const KeyValue& other) const
    {
        return (this->_key < other.getName());
    }

private:
    string _key;
    string _value;
};

class KeyValueSet
{
public:

    KeyValueSet() {
        // put some KeyValue's in the set just for testing
        KeyValue kv1("Dog", "Hound");
        KeyValue kv2("Cat", "NoGood");
        KeyValue kv3("Fish", "Bass");
        theSet.insert(kv1);
        theSet.insert(kv2);
        theSet.insert(kv3);
    }

    KeyValue* getKeyValue(string & name, string & value)
    {
        KeyValue key_value(name, value);
        KeyValue * ret = 0;

        // find by name only, if not found use value as default
        set<KeyValue>::iterator iter = theSet.find(key_value);
        if (iter != theSet.end()) {
            //ret = iter; // compile error
            ret = const_cast<KeyValue*>(&(*iter)); // Is there a better way to do this?
        } else {
            ret = new KeyValue(name,value);
        }
        return ret;
    }

private:
    set<KeyValue> theSet;

};


int main(int argc, char *argv[])
{

    KeyValueSet kvs;

    string s1("Fish");
    string s2("Bass");
    KeyValue* kv = kvs.getKeyValue(s1, s2);

    system("PAUSE");
    return 0;
}

---

Is there an easier way to do this other than the line:
retval = const_cast<KeyValue*>(&(*iter));

I tried the line above it but get a compile error. I think I understand why after do some reading but it seems like there would be an easier way to return the pointer to the object.

All help is appreciated.

Thanks.

In general you do NOT want to do this.

1) What happens if the set (which owns the object) goes out of scope while you are still holding a pointer.

2) (If the pointer is non-const), what happens if you modify the value such that it violates the contraint of the set.

The proper thing to do is to return a copy of the actual item in the set.

Code:

---

KeyValue * ret = 0;

---

You cannot declare a local copy pointer to local variable and return that pointer because the pointee is out of scope or when stack unwinding.

What is stack unwinding ? Simplified explanation needed. Thanks for your help.

This has been pointed by TheCPuWizard.

I hope this help.

Btw, your code has a memory leak. You do a new in the getKeyValue() function and never do a delete on the pointer that's returned.

I'd suggest not returning by reference at all, instead return by value.

Code:

---

        const KeyValue getKeyValue(const string &name, const string &value)
        {
                KeyValue keyValue( name, value );
                std::set<KeyValue>::const_iterator iter = theSet.find( keyValue );
                if( iter != theSet.end() )
                        return *iter;
                return keyValue;
        }

---