post  Pointer Question

cardinals03 (17)   Link to this post
I have the following review question.

A list contains the values 30,40,60 in that order.
p&q are iterators that point to integers on the list.

What will the following print?

1
2
3
4
5
6
 
p = intlist.begin();
p++;
q = intlist.insert(p, 20);
p = intlist.begin();
p++
cout << *p + *q;

I think it is 40. p initially starts at 30 then increments to 40. q then inserts 20 as the value. p then goes back to the beginning of the list (30) and increments to the next value (now 20). Am I right? The thing that is hanging me up is wondering whether or not the value of p is updated by p++ or if it stays 30 (then the output would be 50). Thanks
firedraco (2048)   Link to this post
It would be 40 (assuming the insert function puts the 20 in front of the iterator):


p = intlist.begin();
30 40 60
^p

p++;
30 40 60
___^p

q = intlist.insert(p, 20);
30 20 40 60
___^q
p is probably garbage since IIRC iterators are invalidated by inserts

p = intlist.begin();
30 20 40 60
^p_^q

p++;
30 20 40 60
___^q/p
Last edited on
demosthenes2k8 (128)   Link to this post
Erm...wouldn't that print 40, because they're getting the value at p and adding the value at q, both of which are 20?
firedraco (2048)   Link to this post
Er...yeah >_>

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