CODEWITHSUNDEEP
c++
Dan
Dan

Reputation: 4502

Should C++ attribute names be wrapped in double-underscores?

To tell the compiler to exclude a function from the address sanitizer, the documentation for both gcc and clang say to use an __attribute__ called no_sanitize like this:

__attribute__((no_sanitize("address")))
void hidden_from_sanitizer();

But in the wild (e.g. Facebook's folly library), it seems this attribute is called __no_sanitize__:

__attribute__((__no_sanitize__("address")))
void hidden_from_sanitizer();

GCC and Clang appear to accept both syntaxes, but which should I use? What's the difference? Is wrapping attribute names in double-underscores documented generally somewhere?

Upvotes: 2

Views: 700

Answers (2)

interjay
interjay

Reputation: 110098

GCC documentation says:

You may optionally specify attribute names with ‘__’ preceding and following the name. This allows you to use them in header files without being concerned about a possible macro of the same name. For example, you may use the attribute name __noreturn__ instead of noreturn.

So you can use the double underscores if you want to be 100% safe in a library header file, or if you know of a name conflict with an existing macro.

Upvotes: 3

einpoklum
einpoklum

Reputation: 131527

These are compiler-specific attributes, not C++ language attributes, which use a different syntax, e.g. [[noreturn]] or [[maybe_unused]].

For compiler-specific features - you have to consult your compiler documentation, and there's no general rule.

Upvotes: 2

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