How to use gsl::span to fix No array to pointer decay warning?

Question

I am attempting to resolve the following warning.

warning C26485: Expression 'pNMLink->item.szUrl':
No array to pointer decay. (bounds.3...)

This warning is caused by the following code.

auto pNMLink = reinterpret_cast<PNMLINK>(pNMHDR);
ShellExecuteW(nullptr, L"open", pNMLink->item.szUrl, nullptr, nullptr, SW_SHOWNORMAL);

The extremely limited documentation of the C++ Core Guidelines suggests that the solution is to use a span.

array decay -- use span (from the GSL)

Unfortunately, it gives no information on how to construct that span from the array.

I have tried the following.

gsl::span<wchar_t> url(pNMLink->item.szUrl);

I have tried a number of other options as well. They all result in the same exact warning. What magical incantation do I need to use to avoid the warning?

Not sure about span but the way to avoid array decay that I know of is to pass it by reference. For example (&pNMLink->item.szUrl)[L_MAX_URL_LENGTH] or something like that. — Justin Randall
– Justin Randall, Commented Feb 16, 2018 at 4:53

Nicol Bolas · Accepted Answer · 2018-02-16 06:41:31Z

3

This would appear to be an error in the static analysis tool. How do I know? Because you don't get this warning if you do this:

int arr[10];
gsl::span<int> sp1(arr);

But you do get the warning if you do this:

struct Arr { int arr[10]; };
Arr test;
gsl::span<int> sp2(test.arr);

gsl::span has a constructor that takes array parameters by reference, so when you pass an array directly, there should be no decaying. As shown by sp1, which gives no warning. And there's no C++ reason why fetching the array from a struct would provoke decay when using an automatic variable does not.

So clearly, this is a bug in the analysis tool, a false positive.

answered Feb 16, 2018 at 6:41

Nicol Bolas

481k66 gold badges861 silver badges1.1k bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to use gsl::span to fix No array to pointer decay warning?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related