How to pass structure to function in c++

Question

I created structure Route.h

#include "stdafx.h"
using namespace std;

struct Route {
    string startPoint;
    string endPoint;
    int number;
};

and I need to pass this structure to function. I used reference:

void CreateRoute(Route &route)
{
  int start = rand() % 10;
  int end = rand() % 10;

  if (start == end)
  {
    while(true)
    {
      end = rand()%10;
      if(end != start) break;
    }
  }

  route.startPoint = SetPoint(start);
  route.endPoint = SetPoint(end);
  route.number = SetNumber();
}

but it seems the using of pointers is the better way to do it, but I don't know how to use pointers for it?

Why do you think you should use pointers? I don't see any reason for that. — juanchopanza, Oct 16 '13 at 10:00
"Better" is clearly subjective, but you might also consider making `Route` the return type. — NPE, Oct 16 '13 at 10:00
You might want to have a look at http://stackoverflow.com/questions/57483/what-are-the-differences-between-pointer-variable-and-reference-variable-in-c — Marcello Romani, Oct 16 '13 at 10:01
@juanchopanza Because I have read the using of poiners is more powerful way to do it. — Heidel, Oct 16 '13 at 10:02
@Heidel no, that is just plain wrong. You would use a pointer if there is a chance the input could be null. That's about it. — juanchopanza, Oct 16 '13 at 10:04
In this case, I would just have the function make a new object and retrurn it. Copy can be optimized by move. — Casper Beyer, Oct 16 '13 at 10:09

Casper Beyer · Accepted Answer · 2013-10-16T10:25:20.657

3

In this case, why aren't you simply returning a newly constructed object?

struct route
{
    std::string start_point;
    std::string end_point;
    int number;
};

route make_random_route()
{
    route r;

    int start = std::rand() % 10;
    int end = std::rand() % 10;

    while ( start == end) {
        end = std::rand() % 10;
    }

    r.start_point = make_point(start);
    r.end_point = make_point(end);
    r.number = make_number();

    return r;
}

Its trivial, and with move there is no copy.

edited Oct 16 '13 at 10:25

answered Oct 16 '13 at 10:18

Casper Beyer

2,203
2
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Yes, by now I changed my all function and made `Route` the return type, `Route CreateRoute()`. – Heidel Oct 16 '13 at 10:20

score 2 · Answer 2 · answered Oct 16 '13 at 10:02

2

but it seems the using of pointers is the better way to do it

One of the reasons C++ has references to begin with is to get around the hassle of dealing with pointers, arrows and lots of parentheses.

You could easily convert it to use a pointer type, but the ref type is just cleaner.

void CreateRoute(Route* route);

would be your declaration, and you would call it using

Route route;
CreateRoute(&route);

answered Oct 16 '13 at 10:02

yamafontes

5,552
1
18
18

1

You don't need to call `new` at all. That will just add to the confusion. – juanchopanza Oct 16 '13 at 10:05
It doesnt work if I call it using `CreateRoute(&route[i]);` (I need to pass member of array) but it works if I call it using `CreateRoute(route[i]);` – Heidel Oct 16 '13 at 10:10
You changed the function definition to use arrows instead of dots, right? – yamafontes Oct 16 '13 at 10:12
By now I changed my all function and made `Route` the return type, `Route CreateRoute()`. – Heidel Oct 16 '13 at 10:15

score 1 · Answer 3 · answered Oct 16 '13 at 10:05

1

I think you must improve your C++ basis. Below is my simple answer.

void CreateRoute(Route *route)
{
if (route == NULL)
    return;

int start = rand()%10;
int end = rand()%10;

if (start == end)
{
    while(true)
    {
        end = rand()%10;
        if(end != start) break;
    }
}

route->startPoint = SetPoint(start);
route->endPoint = SetPoint(end);
route->number = SetNumber();
}

answered Oct 16 '13 at 10:05

Kevin

97
2

1

While correct, this does nothing to dispel OP's strange notions about passing a pointer in the first place. – juanchopanza Oct 16 '13 at 10:23

How to pass structure to function in c++

3 Answers3