CODEWITHSUNDEEP
c++vectorcompiler-errorspass-by-reference
Austin
Austin

Reputation: 7319

Why can't I modify a vector that I pass by reference?

This is the first time I'm trying to use pass by reference with vectors. I thought I did it correctly, but I get error: no viable overloaded '=' on the line that tries to assign a[0] = 5

void BubbleSort(vector<int> *a) {
    int n = a->size(), numberOfSwaps = 0;   
    if (n > 0)
        a[0]= 5;
}


int main(){
    // input size and array
    int n;
    cin >> n;
    vector<int> a(n);
    for(int a_i = 0;a_i < n;a_i++){
       cin >> a[a_i];
    }
    // sort
    BubbleSort(&a);
    // print
    for (auto i = a.begin(); i != a.end(); ++i)
        cout << *i << ' '; 

    return 0;
}

edit:

So now that I've been informed that I'm actually passing by pointer, my question is, should I be passing vectors by reference or by pointer, or does it not matter?

Upvotes: 0

Views: 185

Answers (2)

Sam Varshavchik
Sam Varshavchik

Reputation: 118292

vector<int> * is not a reference. vector<int> * is a pointer.

Either change the function to take a reference as a parameter, or use (*a)[0]=5.

However, after you fix this program so that it compiles, when you run it, it will crash immediately as a result of undefined behavior due to accessing non-existent contents of the vector. You have other, multiple bugs to fix, in this code.

Upvotes: 4

Unimportant
Unimportant

Reputation: 2096

You're not passing by reference, you're passing a pointer. You need to dereference the pointer before you can access operator [].

(*a)[0] = 5;

Upvotes: 2

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