CODEWITHSUNDEEP
c++vectoriterator
h.ni
h.ni

Reputation: 21

C++ vector content not changed while using iterator

I have a vector with integer elements {1,2,3,4} and I was trying to remove the last element in my func method. It worked fine when I used pop_back() and back(). But when I used an iterator in the method, it said the last element is still 4.

Also, if I tried to print the last element of the vector back in my main method, it still outputs 4.

Can someone kindly explain to me what I should do if I want to change the content of my vector in a method other than main?

My code:

using namespace std;

void func(vector<int> array) {
    array.pop_back();    
    cout << "array.back() = " << array.back() << endl;

    vector <int>::iterator it = array.end();
    cout << "it.end() = " << (*it) << endl;
}

int main(void) {
   vector <int>  ar;
   ar.push_back(1);
   ar.push_back(2);
   ar.push_back(3);
   ar.push_back(4);
   func(ar);

   cout << "In main = " << ar.back() << endl;

   return 0;
}

It outputs:

array.back() = 3
it.end() = 4
In main = 4

Upvotes: 0

Views: 317

Answers (2)

GooseSerbus
GooseSerbus

Reputation: 1260

You're passing the vector as a value, which means it's copied in the function. If you want to modify it in the function you either need to pass it as a reference (&) or a pointer (*) so that the data in the original vector gets modified, not the copy.

void func(vector<int>& array) // reference

void func(vector<int>* array) // pointer

I recommend using a reference here, as you won't need to worry about null pointers or need to change any of your method (with a pointer you would need to change the '.'s to '->'s).

Upvotes: 4

Sasha Pachev
Sasha Pachev

Reputation: 5336

You need to change passing your argument to func() to be by reference instead of by value like this:

#include <iostream>
#include <vector>
using namespace std;

void func(vector<int>& array) {
    array.pop_back();    
    cout << "array.back() = " << array.back() << endl;

    vector <int>::iterator it = array.end();
    cout << "it.end() = " << (*it) << endl;
}

int main(void) {
   vector <int>  ar;
   ar.push_back(1);
   ar.push_back(2);
   ar.push_back(3);
   ar.push_back(4);
   func(ar);

   cout << "In main = " << ar.back() << endl;

   return 0;
}

then the output becomes:

array.back() = 3
it.end() = 4
In main = 3

Otherwise, you are modifying a copy of the vector that you passed to func(), but not the original one.

Upvotes: 0

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