Are STL vectors pass by reference/address?-CodePudding

I was solving a recursion problem. While solving, I got stuck in a position where I am unable to figure this out:

#include<bits/stdc  .h>
using namespace std;

vector<int> Search(int arr[],int in, int n, int t, vector<int> &v){//v passed as ref.
    if(in == n){
        return v;
    }
    if(arr[in] == t){
        v.push_back(in);
    }
    return Search(arr, in 1, n, t, v);
}

int main(){
    int arr[] = {1, 2, 3, 4, 5, 4, 7, 4, 9, 4};
    vector<int> v;
    v = Search(arr, 0, 10, 4, v);
    for(int i = 0; i < v.size(); i  ){
        cout << v.at(i) << endl;
    }
    return 0;
}

In this code, I had passed the v as reference, but when I tried passing it without a reference then interestingly both of the codes worked.

#include<bits/stdc  .h>
using namespace std;

vector<int> Search(int arr[], int in, int n, int t, vector<int> v){
    if(in == n){
        return v;
    }
    if(arr[in] == t){
        v.push_back(in);
    }
    return Search(arr, in 1, n, t, v);
}

int main(){
    int arr[] = {1, 2, 3, 4, 5, 4, 7, 4, 9, 4};
    vector<int> v;
    v = Search(arr, 0, 10, 4, v);
    for(int i = 0; i < v.size(); i  ){
        cout << v.at(i) << endl;
    }
    return 0;
}

Can you explain why this happens?

CodePudding user response：

In the case of passing by reference you are pushing into the same vector that you pass in.

However when you pass by value you are pushing into a copy of the vector. But then you are returning the vector which returns the local copy, then you are assigning that (eventually) to the vector v in main. That's what makes it look like the code does the same thing even though it does not.