which attribute syntax should i use ("[[gnu::attr]]" or "__attribute__ ((attr))")

[Kallinteris Andreas]

__attribute__ ((pure))
int foo() {return 2;}

[[gnu::pure]]
int bar() {return 2;}

Both of those attributes do the same thing the second one is not documented in GCC manual

c++ core guidelines recommend using the second method (http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#gsl-guidelines-support-library) (I think)

which one is the preferred method

[jonnin]

not sure it matters since it is nonstandard and unportable?

[mbozzi]

Prefer the latter because it uses the standard attribute syntax.