We use both internally, actually. GNU gcc/g++ and IBM xlc/xlC all support doing this: #if defined(... all the compilers above ...) # define PRAGMA_ONCE _Pr

We use both internally, actually. GNU gcc/g++ and IBM xlc/xlC all support doing this: #if defined(... all the compilers above ...) # define PRAGMA_ONCE _Pragma("once") #else # define PRAGMA_ONCE #endif Specifically, MSVC and HP cc/aCC do not support it. Oracle cc/CC does the #ifndef/#define detection and internally does something similar to what the pragma enables in other compilers.