CODEWITHSUNDEEP
c++functiontemplatesiteratorcontainers
LaoJiu
LaoJiu

Reputation: 69

container as a function parameter

#include <iostream>
#include <vector>

using namespace std;

void factorial(vector<int> ivec, typename vector<int>::iterator iter) 
{
    vector<int>::iterator it;
    for (it = iter; it != ivec.end(); it++)
         cout << *it << endl;
}

int main()
{
    vector<int> ivec;
    for (int i = 1; i < 8; i++) 
        ivec.push_back(i);

    factorial(ivec, ivec.begin());

    return 0;
}

In visual studio 2015,it shows,

enter image description here

but if I let ivec to be a reference type(vector<int> & ivec), it will work successfully.

Why?

The code is bad, bad, bad,,, so please you just focus on the question.

Upvotes: 0

Views: 197

Answers (2)

Edwin Rodr&#237;guez
Edwin Rodr&#237;guez

Reputation: 1257

Because you're passing the vector by value copying it and making it != ivec.end() undefined.

When you pass by value you're doing something like

vector<int> v1 =  {1,2,3,4,5,6,7};
vector<int> v2 = v1; 
//v2 is a copy of v1

v1.end() == v2.end();
//comparing end of different vectors don't have any sense.

When you pass by reference you're doing something like

vector<int> v1 = {1,2,3,4,5,6,7};
vector<int>& v2 = v1;
//v2 is a reference to v1, it's like an alias

v1.end() ==  v2.end();
//it makes sense because v2 is v1, not a copy

Or if you're more familiar with pointers

vector<int> v1 = {1,2,3,4,5,6,7};
vector<int>* v2 = &v1;

v1.end() ==  v2->end();

Upvotes: 0

lapinozz
lapinozz

Reputation: 310

Because iterator are relative to the container you get them from. Since you are passing your vector by value, it's like a second vector, and it doesn't make send to compare an iterator from the first vector and an iterator from the copied one.

Upvotes: 1

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