Problem with list (STL)

[hello 12345]

I have been trying to manipulate data which has been stored as list of objects in a separate class but since I dont have very solid concepts in STL I am failing again and again.
i tried a basic code and it isn't working can any one help?

class testclass
{
public:	int a;
	list<int> b(10);

};
int main()
{
	testclass obj1;
	for(int i=0;i<obj1.b.size();i++)
	{
		push_front(i);
	}
	
}

[MrHutch]

If you're just trying to push the data to the list, your push_front line should be:

obj1.b.push_front(i);

[hello 12345]

Still there is error. The error is some thing else:

list3_test.cpp:8:14: error: expected identifier before numeric constant
list3_test.cpp:8:14: error: expected ‘,’ or ‘...’ before numeric constant
list3_test.cpp: In function ‘int main()’:
list3_test.cpp:14:22: error: ‘obj1.testclass::b’ does not have class type
list3_test.cpp:16:9: error: ‘obj1.testclass::b’ does not have class type

[ne555]

and it isn't working

Be more specific, please.
_ Compile errors
_ Segmentation fault
_ Unexpected results
_ Fried processor

Edit:

	for(int i=0;i<obj1.b.size();i++)
	{
		obj1.b.push_front(i); //this will increment the size of the list
	}

There is no reserve for list. It makes no sense.

[MrHutch]

Oh, I see.

I'm not sure you can call the list's constructor like that inside of a class. Try removing the (10) and see if it works. If you want to set the size, one solution is could be to use a pointer to a list:

class testclass
{
public:
   testclass();
   list<int> *b;
};

testclass::testclass()
{
   b = new list<int>(10);
}

Don't forget to delete appropriately when you're done.


Also, I think you're probably better off using an iterator to loop through the list. If you want to use the regular loop, you can't use the size() function of the list, though, because as you push to the list, you're incrementing the size (as ne555) says, so you're always expanding and your loop end condition is never met.

You could do something like:

int list_size = obj1.b.size();

for (int i=0; i < list_size; i++)
{
   // Push stuff here
}

I should note that what you're doing when you're pushing to the list is adding new elements to the front, not assigning to the already existing elements.

[viliml]

@hello 12345: Try removing the constructor, and don't loop untill obj.b.size(), becoese it always increases! Loop just to 10.

[ne555]

@iHutch105

Bjarne Stroustrup wrote:

Code that creates an object using new and then deletes it at the end of the same scope is ugly, error-prone, and inefficient.

[hello 12345]

Finally understood. Forgot that the concept of list is to let us add objects dynamically thats why no need for that 10 :)
Program is also working.
Still have one doubt. If i want to specify the number (of objects in a list of objects of a class) where the list is a member of a second class?
OR

class a
{
list<b> bobjects;
};
class b
{
members;
}

If i want to specify the length of list bobjects statically Is there a method?

[MrHutch]

@ne555

Is there a static, non-C++11 way to do it?

[ne555]

If you want to call a constructor, use an initialization list.
testclass::testclass(): b(10){}

@hello 12345: I don't understand what you want to do.
Reserve makes no sense with lists. ¿do you want an upper limit?

[MrHutch]

Init list! Of course, duh.

Cheers, ne555.