vector as an argument for recursive function in c-CodePudding

I want to have function like one in the title, but when I declare it like this,

void function(vector<int> tab, int n)
{
    if(n > 0)
    {
        tab.push_back(n);
        function(tab, n - 1);
    }
}

it isn't working, because tab is still blank.

CodePudding user response：

You're taking tab by value - each recursive call will operate on a new copy of tab.

You'll want to pass tab by reference:

void function(std::vector<int>& tab, int n) { ... }

CodePudding user response：

If you want to modify a vector that was declared outside the scope of your function you should pass it by reference

void function(vector<int>& tab, int n)

Otherwise each call to function will create a function-local copy of tab and only mutate that copy, not the original external vector.

CodePudding user response：

Either you need to declare the first parameter as having the referenced type std::vector<int> & like

void function( std::vector<int> &tab, int n);

Or you should redefine the function such a way that it will return a vector.

Here is a demonstration program.

#include <iostream>
#include <vector>

std::vector<int> function( int n )
{
    std::vector<int> v;

    return n > 0 ? v = function( n - 1 ), v.push_back( n ), v : v;
}

int main()
{
    auto v = function( 10 );

    for (auto &item : v)
    {
        std::cout << item << ' ';
    }
    std::cout << '\n';
}

The program output is

1 2 3 4 5 6 7 8 9 10