Preprocessor macro expanding to a type attribute
#include <SYS/TYPES.H>
void __SCANF_ATTR__(a,b) function(args...);
This macro expands to a compiler-specific attribute telling that the function processes a scanf-like format string.
It advises the compiler to print a warning if argument types do not match "%" strings in the format string.
When using the gcc compiler, this macro expands to __attribute__((__format__(__scanf__(a,b))))
.