Returning array from function

Question

Been trying to get this to work for hours with many different methods but still can't get it to work...

Main class:

WinHandle wh;
int* myarr;
myarr = wh.getpos;
cout << "left: " << *(myarr) << endl;

WinHandle.cpp class:

int* WinHandle::getpos(){
  int pos[4];
  //code
  pos[0] = 2;
  //code

  return pos;
}

WinHandle.h file:

int* getpos();

That's just my last method, tried various others to no avail. Any help?

Keep getting

non-standard syntax; use '&' to create a pointer to member

and

cannot convert from 'int *(__thiscall WinHandle::* )(void)' to 'int *'

1. myarr = wh.getpos();. 2. You're trying to return a pointer to local variable so it will become dangled (didn't you get any compile warnings?). — songyuanyao
– songyuanyao, Commented Jul 10, 2016 at 2:11
why are you using pointers in this case? If you're using C++, it's best std::array, or std::vector, or one of other beautiful containers. — Jepessen
– Jepessen, Commented Jul 10, 2016 at 9:55

Sam Varshavchik · Accepted Answer · 2016-07-10 02:14:40Z

2

A plain array cannot be returned directly from a function.

Use std::array, instead.

answered Jul 10, 2016 at 2:14

Sam Varshavchik

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Comments

SergeyA · Accepted Answer · 2016-07-10 02:14:25Z

1

Your immediate source of compilation error is wrong syntax. When you are calling the function, you need to call it with parenthesis: wh.getpos(). However, this is a lesser of a problem. A much bigger problem is that you are returning an array which is local to your function. This won't do, this array will be destroyed once you exit the function, and you will end up with a pointer to deleted object. Say 'Hi' to undefined behavior.

To fix the problem, you need to return either std::vector or std::array.

answered Jul 10, 2016 at 2:14

SergeyA

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3 Comments

Peter Over a year ago

Or make the array being returned a member of WinHandle. Then the pointer returned by wh.getpos() is valid for as long as wh continues to exist.

SergeyA Over a year ago

@Peter, might be a valid option depending on the design of the class.

Peter Over a year ago

Sure. That's why I suggested it as an additional option to fix the problem.

maja · Accepted Answer · 2016-07-10 09:50:27Z

0

The best solution is to use std::array (or std::vector) because it's the most flexible. Otherwise, you could create the array outside the method, then use a reference parameter to operate on it inside wh.getpos().

answered Jul 10, 2016 at 9:50

maja

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