Thread: 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:

#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;
}

The output is:

Code:

9
9
====
0
0

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.

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

Thanks a lot!

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

Originally Posted by pheres

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

Code:

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.

Originally Posted by Mike Borozdin

I'm usually careful with variables.

And that is exactly the reason why to limit their scope

Ok, just like

Code:

int i

in the 'for' loop.