Declaring a constant literal string with const reference versus const variable

Question

I have to name windows with constant literal strings. The names will be referenced everywhere so I need to cache them with variables. My question is

Do I need to declare the variables as const references as follows

const string& srcWnd = "Source Window";

instead of

const string srcWnd = "Source Window";

?

Is there any difference?

Define "need" - both of those will construct `string` objects, what exact difference are you asking about? — UnholySheep, Apr 03 '19 at 21:53
@ArtificialHairlessArmpit What exactly do you mean by "cache the names"? — Michael Kenzel, Apr 03 '19 at 21:56
If you want a reference to literal itself rather than to `std::string` object then you should write `auto const & srcWnd{"Source Window"};` — user7860670, Apr 03 '19 at 21:56
Probably similar question from earlier today: https://stackoverflow.com/questions/55498738/how-to-share-global-constants-with-minimum-overhead-at-runtime/55499098 — Michael Kenzel, Apr 03 '19 at 22:03
If you are constructing `std::string` class instance then content of array baking string literal will be always copied. — user7860670, Apr 03 '19 at 22:06
Given that we're talking about window names here, do these really have to be `std::string` (assuming that `string` up there is `std::string`)? Because if you're concerned about efficiency/avoiding copying then the first thing you'll probably wanna do is not have it be an `std::string`… — Michael Kenzel, Apr 03 '19 at 22:07
@ArtificialHairlessArmpit ok, then probably just go with the `const std::string` approach as suggested in the answer below. Just be aware that a global `std::string` will almost necessarily mean that you're copying the string from a string literal object into the buffer owned by the `std::string` at load time. If the names are expected to be `std::string` that's most likely just fine anyways… — Michael Kenzel, Apr 03 '19 at 22:16

score 2 · Accepted Answer · answered Apr 03 '19 at 22:05

I don't see any significant difference between the two, but I suggest using the plain string (option 2):

const string srcWnd = "Source Window";

You don't win anything by using a reference. And if you use a reference, the code becomes more obscure, because by using a reference you rely on temporary lifetime extension. If someone doesn't remember lifetime extension rules clearly, they might need to look them up just to be sure that the code is valid.

Declaring a constant literal string with const reference versus const variable

1 Answers1