List iteration problem, it resets values

Hello!

Sorry for asking a probably stupid question, but I can't solve the problem. I'm writting some application and got in stuck with a part of it. Here I post a simplified part of it.

Code:

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#include <list>
#include <iostream>
#include <conio.h>
using namespace std;
class Object {
        private:
                int value;
        public:
                Object(void);
                int getValue(void);
                void setValue(int value);
};
int main(void) {
        Object one;
        Object two;
        list<Object> objects;
        list<Object>::iterator i;
        objects.push_back(one);
        objects.push_back(two);
        Object object;
        for (i = objects.begin(); i != objects.end(); i++) {
                object = *i;
                object.setValue(9);
                cout << object.getValue() << endl;
        }
        cout << "====" << endl;
        for (i = objects.begin(); i != objects.end(); i++) {
                object = *i;
                cout << object.getValue() << endl;
        }
        getch();
        return 0;
}
Object::Object(void) {
        value = 0;
}
int Object::getValue(void) {
        return value;
}
void Object::setValue(int value) {
        this->value = value;
}

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The output is:

Code:

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9
9
====
0
0

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In the first loop I change the values of 'value' property and output it immediately to check, then in the second loop I just output the values but they are zero again.

object = *i;

makes a copy of the object in the list. you modify and output the copy in the first loop and make and output a new copy in the second loop

this one should do it:

Code:

---

for (i = objects.begin(); i != objects.end(); i++) {
                i->setValue(9);
                cout << i->getValue() << endl;
}
cout << "====" << endl;
for (i = objects.begin(); i != objects.end(); i++) {
      cout << i->getValue() << endl;
}

---

also it would be better to minimize the scope of your vars, for example like that:

Code:

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for ( list<Object>::iterator i = objects.begin(); i != objects.end(); i++) {

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instead of declaring i outside the for-loop. that could lead to unwanted sideeffects later

Quote:

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Originally Posted by pheres

object = *i;

makes a copy of the object in the list. you modify and output the copy in the first loop and make and output a new copy in the second loop

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Thanks a lot!

Although, by the moment I've realized this myself. But still thanks.

Quote:

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Originally Posted by pheres

also it would be better to minimize the scope of your vars, for example like that:

Code:

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for ( list<Object>::iterator i = objects.begin(); i != objects.end(); i++) {

---

instead of declaring i outside the for-loop. that could lead to unwanted sideeffects later

---

Thanks for your advice, but I'm usually careful with variables.

Quote:

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Originally Posted by Mike Borozdin

I'm usually careful with variables.

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And that is exactly the reason why to limit their scope :)

Ok, just like

Code:

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int i

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in the 'for' loop.