return structure vs pass Reference variables

Question

Which one is better if I have to return a string as well as an array from a function.

Create a structure containing string and array, populate that and return the instance of that structure.

Consider I have to send string "status" and an array "ids".

    struct ReturnValues {
      string status;
      int ids[10];
    };

use it as:

ReturnValues returnValues;
returnValues = func();

Consider that func() returns the object of ReturnValues

Pass one of them as referenced variable and return the other.

As:

int ids[10];
string status = func(ids);

Consider that func takes ids as referenced variable

string func(int& ids) {
  //Some code
  return status;
}

Pass both as referenced variables returning void.

As:

int ids[10];
string status;
func(ids, status);

Consider that func takes ids and status as referenced variables

void func(int& ids, string& status) {
  //some code;
}

It depends on your compiler optimization settings. – Jean-Michaël Celerier Feb 26 '16 at 11:39 — Jean-Michaël Celerier, Feb 26 '16 at 11:39

score 1 · Answer 1 · answered Feb 26 '16 at 11:44

1

Strictly from a performance standpoint, it would give the compiler the most leverage to optimize if you do :

struct ReturnValues {
  string status;
  int ids[10];
};

and

ReturnValues returnValues = func();

Doing

ReturnValues returnValues;
returnValues = func();

will decrease performance since return-value optimization cannot take place : http://goo.gl/5Cfmw2

answered Feb 26 '16 at 11:44

Jean-Michaël Celerier

7,412
3
54
75

Right, and the second version should also be avoided for other reasons: You cannot make returnValues const, somebody might try to access the uninitialized variable and finally it is more verbose. – Frank Puffer Feb 26 '16 at 12:40

score 0 · Answer 2 · answered Feb 26 '16 at 11:46

I would definitely go for the 1st version. Functions that modify their arguments tend to make the code more difficult to understand and test.

If you are worried about performance: Practically all compilers will use return value optimization here. So this should not be an issue, maybe except in some exotic cases.

score 0 · Answer 3 · answered Feb 26 '16 at 11:47

Personally I would either group them together either into a predefined struct as you did or use std::pair or tuple if you don't want to define one explicitly. My feeling is that things that belong together belong together (if you'll forgive the tautology). Either way I would consider using std::array if the array length is fixed or std::vector (or some collection type) if not. Am not a fan of level C type arrays such astype A[10] I would probably just return them as a return value simply because it shows the intent "Get me one of these things with ints and strings in it" and let the compiler sort it out

return structure vs pass Reference variables

3 Answers3