Help with vectors with multiple CPP files

[pharoah0110]

I've just stepped into the realm of using multiple files; so far, all has gone well...until...
I'm having a boatload of trouble trying to figure out a solid way to "spread" a vector across multiple .cpp files.
A simplified example of what I'm trying to do:
main cpp:

#include <iostream>
#include <vector>
#include "Header.h"

using namespace std;

vector<int>vec(10);
int main()
{
	setit(&vec);
	return 0;
}
  

Header.h:

#ifndef HEADER_H
#define HEADER_H

extern std::vector<int>vec;
void setit(vector<int>*temp);

#endif 

func.cpp:

#include <iostream>
#include <vector>
#include "Header.h"

using namespace std;

void setit(vector<int>*temp)
{
	for (int n{}; n < 10; n++)
	{
		temp->push_back(n * 20);
	}
}

Basically, I need to be able to pass vec to the "setit" function as a pointer.
In a single file, this would work like a charm, but I haven't been able to get this to work. Multiple compiler errors.
For whatever reason, in header.h the lone definition

extern std::vector<int>vec;

works fine, until I put the header in header.h, which is when intellisense starts complaining.
So, all being said, what exactly is the "proper" way to make a vector available across multiple .cpp files?
Any help would be most appreciated.
Cheers!

[keskiverto]

You don't want to "spread".
You don't want global variables.
You should not want pointers.

Use reference parameters:

#include <vector>
#include "Header.h"

int main()
{
  std::vector<int> vec(10);
  setit( vec );
  return 0;
}

#ifndef HEADER_H
#define HEADER_H
#include <vector>

void setit( std::vector<int> & temp );

#endif  

#include <vector>
#include "Header.h"

void setit( std::vector<int> & temp )
{
  for ( int n = 0; n < ????; ++n )
  {
    temp[n] = n * 20;
  }
}